98343 comp stud glos of terms - web1.muirfield-h.schools...

Glossary of TermsThird Edition

to accompany the

2 Unit (General)

2/3 Unit (Common)

3 Unit (Additional)

Computing Studies Syllabuses

© Board of Studies NSW 1998

Published byBoard of Studies NSWGPO Box 5300Sydney NSW 2001Australia

ISBN 0 7313 1375 5

Tel: (02) 9367 8111

Third edition, September 1998

98343

Introduction

This glossary supports the Computing Studies syllabuses released in 1994.

It is organised in two parts:

■ Terms Used in Computing Studies

Each of the various courses comprising the syllabuses makes mention of a number of

terms. The terms appropriate to each course are listed in this part, together with any

additional terms helpful and relevant to the course.

■ Glossary of Terms

The purpose of the glossary is threefold:

• while recognising both the rapidly changing nature of information technology, and the

(often subtle) variations in meaning of terms as used by the authors of different texts,

the glossary seeks to provide clear definition of terms appropriate to the courses

comprising the Computing Studies syllabuses;

• to give some indication of the depth of treatment of topics appropriate to the

syllabuses;

• to provide detailed cross-referencing, thus enabling the reader to acquire further

understanding of the content of the syllabuses.

The Arrangement of Glossary EntriesIn general, the natural lead word of a phrase is taken to be the master word, even if it is an

adjective qualifying a noun — for example light pen appears under light, and object code

appears under object.

Common abbreviations and acronyms are listed and, where appropriate, are cross-referenced.

Cross-referencingCross-references are indicated by the use of italics.

Where a cross-referenced term occurs more than once in an entry, only its first occurrence is

italicised.

Cross-referencing is also indicated by the use of the terms See, See also or Compare with.

See directs the reader to another entry.

See also indicates that another entry contains further useful information on the topic.

Compare with refers to a related but contrasting term that will assist in the reader’s broader

understanding of the topic.

Use of Bold FaceBold face printing is used for emphasis.

3

Terms Used in Computing Studies

Preliminary Course

Topic 1 • modifier keys, QWERTY keys, SHIFT key, ESC key,

Basic Skills and Concepts CONTROL key, ALT key, OPTION key, numeric

keypad

• fetch-execute cycle

• ergonomics

Topic 2 • system, subsystem, data, personnel, procedure,

Computer-based Systems environment, input, output, processing, control, system

software, utility software, application software, boundary

• data security

Topic 3 • algorithm, sequence, binary selection, multi-way selection,

Algorithms repetition, pre-test, post-test

(See Methods of Algorithm Description (2nd edn))

Topic 4 • run (an application), application software, command-

Application Software Usage driven, menu-driven

Word processor: • editing, block-action, character, cursor, cut-and-paste,

default, file, font, global search and replace, grammar

checker, header, footer, justification, insert mode,

overwrite/overstrike mode, line editor, macro, mail-merge,

OCR, outline package, pagination, proofreading,

proportional spacing, ruler, scroll, search and replace,

stroke weight, style, style checker, template, text editor,

text file, type face, type style, type size, white space

character, word processor, wordwrap, WYSIWYG

Database: • data, database, database management system, data

dictionary, field, form view, record, table view

Spreadsheet: • cell, absolute cell address, address, cell address, cell

pointer, chart, column, model, relative cell address,

spreadsheet

Communications: • serial communication, parallel communication, modem,

bit rate, parity, file transfer, protocol, electronic mail

4

Glossary of Terms

2 Unit (General) Course

Topic 1 • ‘what if’ prediction

Spreadsheets • cell, absolute cell address, address, cell address, cell

pointer, chart, column, graph, label, macro, model, relative

cell address

• template

• formula, function

• chart, graph

• macro

• file conversion filter, clipboard, data interchange format

Topic 2 • database management system (DBMS), distributed

Databases database, field, record, flat file, primary key, secondary

key, logical record


• mail merge

Topic 3 • anti-aliasing, bit-mapped, buffer, composite video,

Graphics coordinates, dithering, GIF file, paint, palette, paste, pixel,

pixel averaging, resolution, frame buffer, RGB,

storyboard, composite video, delta information, field,

insert edit, interlacing, titling

• distorting, cropping, sizing

• colour depth, data compression, scan, warp

• file conversion filter

• cel, cel-based, cel buffer, cross-fade, frame, time code,

tween, morphing, path-based


Topic 4 • resolution

Desktop Publishing • template, master page

• callouts



5

2 Unit (General) Course (continued)

Topic 5 • answer mode, asynchronous, auto-answer, auto-dial, baud,

Computer Communication bits per second, Bps, communications software, dumb

terminal, encryption, full-duplex mode, half-duplex mode,

host computer, leased line, local area network, modem,

optical fibre, packet, packet switching, parallel

transmission, parity bit, repeater, serial transmission,

simplex mode, start bit, stop bit, synchronous,

telecommunications, terminal, time-sharing

• LAN, WAN

• network, node, star network, ring network, bus network

• login, logout, password

• upload, download

• electronic mail

• electronic bulletin board, password

• remote database

• protocol, file conversion filter, clipboard, data interchange

format

2/3 Unit (Common) Course

Core Topic 1 • system development cycle

Computer-based Systems • requirements definition, feasibility study

• organisation chart, data flow diagram, flow chart

• data dictionary, decision tree, decision table, Gantt chart

• copyright, ethics, equity, employment, nature of work,

power and control, environment

Core Topic 2 • structured data types: array (1-dimensional), record,

Algorithm Design sequential access, direct access

• desk checking, sorting, bubble sort, insertion sort,

selection sort, linear search, binary search

• top-down design, step-wise refinement

Option Topic 1 • artificial intelligence, intelligent system, expert system

Applied Artificial Intelligence shell, inference engine, forward chaining, backward

and Expert Systems chaining

• neural network, natural language processing, voice

recognition, robotics, artificial vision, knowledge

engineering

• fuzzy logic

• intelligent robot

6

Glossary of Terms

2/3 Unit (Common) Course (continued)

Option Topic 2 • answer mode, asynchronous, auto-answer, auto-dial, baud,

Computer Communications bits per second, Bps, communications software, dumb

terminal, electronic mail, encryption, full-duplex mode,

half-duplex mode, handshaking, error correction, error

detection, host computer, leased line, modem, node,

optical fibre, packet, parameter, parity bit, protocol,

receive mode, simplex mode, start bit, stop bit,

synchronous, telecommunications, terminal, terminal

emulation, time sharing, X-modem, Z-modem

• serial transmission, parallel transmission, bus network,

collision detection, ethernet, local area network, login,

logout, ring network, star network, password, repeater,

token ring, wide area network

• upload, download, file transfer protocol

Option Topic 3 • block diagram, control system

Computer-controlled Systems • sensor, actuator, controller, continuous system, batch

system, discrete system

• damping

Option Topic 4 • binary, decimal, octal, hexadecimal

Computing Technologies • BCD, EBCDIC, ASCII

• one’s complement, two’s complement, sign and modulus,

• logic gates, truth tables, full-adders, half-adders, flip-flop

• laser, optical fibre, CD ROM, laser printer, magneto-

optical storage

Option Topic 5 • data, database, hierarchical database, network database,

Database Design relational database

• database management system (DBMS), data dependence,

data independence, data dictionary, data hierarchy, data

redundancy, data validation, distributed database, field,

record, flat file, primary key, secondary key, logical record,

schema

• searching, selection

• database administrator

• data security, data integrity


7

2/3 Unit (Common) Course (continued)

Option Topic 6 • anti-aliasing, bit-mapped, composite video, coordinates,

Graphical Techniques dithering, GIF file, HLS, leading, paint, palette, paste,

pixel, pixel averaging, resolution, frame buffer, RGB,

frame, field

• aspect ratio, non-reproducible blue, buffer, colour register,

colour value, render, polygon

• interlace, raster display, time code

• spline, Beziér curve, gradient fill, wire frame

Option Topic 7 (For current Option Topic see Technological and Applied

1995 onwards Studies Stage 6 KLA Handbook)

Multimedia • hypertext, hypermedia

• storyboard, tween, cross-fade, cel buffer, cel, mask or

masking, insert edit

• MIDI

• composite video, delta information, titling

3 Unit (Additional) Course

Topic 1 • languages: machine, assembly, procedural, declarative,

Theory and Practice of object-oriented

Computer Programming • sequential programming paradigm, event-driven

programming paradigm

• array, record, string (array of characters), file

• identifier, operator, operand, control structure, syntax,

railroad diagram, syntax diagram, Backus-Naur Form

(BNF), Extended Backus-Naur Form (EBNF)

• compiler, interpreter, incremental compilation, source

code, object code

• stub, debug, flag

• font, alignment, justification,

• algorithm, code, variable, procedure (subprogram),

comment

• storyboard, IPO chart, structure diagram, function chart

Topic 2 • simple data types, structured data types, one- and multi-

Software Implementation dimensional arrays, simple record, array of records, file,

validation, preprocessing

• maintenance coding

• syntax error, run-time error

• desk-check, run-time check

• prototype

8

Glossary of Terms

Glossary of Terms

absolute address See address (1).

absolute cell address See address (2).

accumulator One of the registers present within the CPU. It stores the

result of the latest computation carried out by the CPU.

See register.

actuator A device under the control of a signal from a controller that

performs a mechanical action.

Compare with sensor.

address (1) The number given to identify a particular storage location

in the computer’s memory.

There are two forms of address: absolute address in which the

location is a unique number and relative address in which the

location is given by a numerical offset from a base address.

(2) A spreadsheet cell is referred to by its cell address.

Examples of the common methods are D5 and R5C4, both

of which refer to the intersection of the fourth column and the

fifth row.

The terms absolute and relative cell addresses are

encountered particularly when formulas and functions are

copied from one cell to another.

Absolute cell addresses, when copied, are not changed while

relative cell addresses, when copied, reflect the relocation of

that cell’s position.

address bus The communications line over which the address of a data

item is transferred to the control unit.

Compare with data bus.

AI Abbreviation for artificial intelligence.

algorithm A series of unambiguous instructions or procedural steps that

will result in the solution to a specific problem within a finite

time. Algorithms can be described in many ways, eg

pseudocode, flowchart.

A


9

ALT key One of the modifier keys which provides an alternative set of

signals generated by combining a press of the ALT key with

another.

See modifier key.

ALU Abbreviation for arithmetic and logic unit.

analog computer A computer that uses data in analog rather than digital form.

Compare with digital computer.

analog/analogue Representing and measuring numerical quantities by means

of continuously variable (as opposed to discrete) physical

quantities such as currents, voltages or mechanical gears.

Compare with digital.

analysis The third stage of the system development cycle. This involves

the study and identification of the input, processes and output

of the existing system. Tools that can be used include Gantt

charts, data dictionaries, decision trees and data flow diagrams.

answer mode The way in which the modem is operating — answering the

call. This mode is characterised by the use of the lower of the

two frequencies used by a modem in full-duplex

communications, eg 1200/2400 bps. The lower rate is used

for data transmitted to answer the call.

Compare with originate mode.

anti-aliasing The process of removing faults such as jaggies in computer

images caused by the physical size and shape of the pixel.

See jaggies, pixel averaging.

application A particular task or area in which a computer system is used.

Sometimes a contracted form of application software or

application package.

application software Software that performs a specialised task. It carries out the

functions of one (or more) applications.

Compare with system software.

argument An independent variable or constant that gives to a command,

instruction or function the information it needs to perform an

operation.

In programming, it is also the value of a parameter passed

between a calling program and the called subprogram.

10

Glossary of Terms

arithmetic and logic unit The part of the central processing unit capable of mathematical

and logical operations.

Abbreviated to ALU.

arithmetic process A process which carries out an arithmetic operation on

numeric data.

array A data structure in which a collection of data items of the

same type can be treated as a single entity. Individual data

items are identified by an index or subscript.

artificial intelligence The science of making machines that mimic human

behaviour. Computers are used in such a way that they

perform operations which are similar to human abilities of

learning and making decisions.

artificial vision The process by which a computer perceives or recognises

objects in the external world.

ASCII Acronym for American Standard Code for Information

Interchange. An eight-bit code for the binary representation

of 256 characters within the computer. Pronounced ass-key.

Compare with EBCDIC.

aspect ratio A way of describing the shape of an image by reporting the

ratio of picture width to height, eg the usual ratio for

television is 4:3 or 1.33:1.0.

assembler A piece of software which changes a program written in

assembly language into machine language. The assembler

produces one machine instruction for each assembly language

instruction.

assembly language A low-level language which is written using a mnemonic

code (eg LDA, STO) as opposed to binary digits. An

assembly language is specific to the CPU used in the

computer.

Compare with machine language.

assignment A process in which a value is allocated to a variable.

asynchronous A system of data transmission in which transmission of a unit

of data is independent of a time code.

See also start bit, stop bit.

Compare with synchronous.

attribute (1) A defined property of an entity or object.

(2) See relational database.


11

auto-answer capability The ability of a modem to receive and respond to incomingcalls under the direction of a computer and without userintervention.

auto-dial capability The ability of a modem to dial a telephone number under thedirection of a computer and without user intervention.

backing store See secondary storage/memory.

backup A copy, on disk or tape, of software or data that is made bythe user to guard against accidental loss.

Backus-Naur form A metalanguage used to define the syntax of a programminglanguage. Named after its two authors. Abbreviated to BNF.

See also BNF, EBNF, Extended Backus-Naur form, railroaddiagrams.

backward chaining The process of determining the facts that lead to a conclusionin an expert system.

Compare with forward chaining.

banner headings Short and concise eye-catching statements to help the readerdecide whether or not to read the body of an article. Theyshould be clearly differentiated from body copy.

batch A collection of data prepared for input as a single unit.

See batch processing.

batch processing A method of processing data in which transactions arecollected and prepared for input as a single unit. When theprogram is executed there is no interaction between user andcomputer.

baud A unit used to measure the speed of transmission in acommunication medium. It measures the number of timesper second the medium can change its state, ie the number ofdiscrete signals per second.

Compare with bits per second.

BCD Acronym for Binary Coded Decimal, a method of encodingdata for input to a computer.

See also ASCII.

B

12

Glossary of Terms

Beziér curve A smooth curve controlled by the position of a small number

of individual points.

binary digit A digit in the binary number system.

See also bit.

binary number system The number system in which the base is two. It uses the

digits 0 and 1.

binary search An algorithm used to search structured data. The data must

be ordered in either ascending or descending order. The

algorithm repeatedly divides the data to be searched into two

parts, discards one part and searches the other until either the

target is found or it is determined that the target is not

present.

See searching.

Compare with linear search.

binary selection A control structure in which a choice between two

alternatives is made based upon the truth or falsity of a

condition. Usually implemented as an IF-THEN-ELSE

structure.

Compare with multi-way selection.

bit A contraction of binary digit. A bit is either a 0 or a 1.

bit map A section of memory consisting of a series of zeroes and ones

corresponding to pixels on the screen. In colour a number of

bits are used to represent the colour value of each pixel.

bit-mapped A correspondence between memory locations and elements of

the output pattern on various output devices.

bit-mapped printer An output device which produces output patterns on an

element-by-element basis determined by the contents of

corresponding memory locations.

Compare with character printer.

bit-rate The speed with which bits of data can be transmitted or

received over a communication medium. Usually measured in

bits per second.

bits per second Abbreviated to Bps. A unit used to measure the speed of

transmission in a communication medium. It measures the

number of bits of data that are transmitted (or received) in

one second.


13

black box A term used to indicate any component of a computer-basedsystem for which the user need not know the details of itsinternal operation.

block graphics A form of graphics in which the pixels on the screen can becontrolled only as blocks. Each block corresponds to a singleelement of the whole graphics display.

block-action An action carried out on a selected block of data in anapplication.

See also cut-and-paste.

BNF Abbreviation for Backus-Naur form.

BNF is a metalanguage used to define the syntax of aprogramming language. It uses the following symbols:

‘is defined as’

(or) indicates a choice between

alternatives

non-terminal symbol a symbol still to be defined

< > used to enclose non-terminalsymbols

terminal symbol is used as written

See also Backus-Naur form, EBNF, Extended Backus-Naurform, railroad diagrams.

body of loop The set of instructions within a loop that is repeated.

boiler plate material A term used in word processing. A block of text that is defined,stored on disk and then copied to different points in adocument or to different documents.

bold face Describes characters constructed by using heavy, thick lines.

See also stroke weight.

Boolean algebra A set of rules, laws and theorems by which logical operationscan be expressed and solved.

A Boolean expression is either true or false.

Boolean operator An operator which acts upon Boolean variables and values.The list of Boolean operators includes AND, OR and NOT.

Boolean variable A variable that can only take values which are either true orfalse.

boundary The delineation between a system and its environment.

¨ -¨ -

14

Glossary of Terms

boundary conditions A term used to refer to the values of variables and/or

expressions that determine which choice of the available

alternatives is to be taken. Test data should normally be

designed to specifically test all boundary conditions.

See also testing.

box A term used in desktop publishing which refers to the

surrounding of a component by a rectangular boundary.

Often used to separate parts of a document or to create a tear

off coupon.

A small (empty) box may be used to provide space for a user

to respond to a question on the written document or to

indicate the end of an article.

Bps Abbreviation for Bits per second.

bubble sort A form of sorting by exchanging pairs of elements that are out

of order, in a sequence of passes through the data structure,

until no such pairs exist. On each pass, one of the elements

(the larger or smaller of each pair depending upon the

criterion for exchanging) travels to an end of the data

structure like a bubble in a liquid.

Compare with insertion sort, selection sort.

buffer A temporary storage for data, normally used to accommodate

the difference in the rate at which two devices can handle

data during a transfer.

bus A parallel group of wires which carry signals having a

common function to and from different parts of a computer

system.

bus network A communications network in which several devices are

connected to a single communications channel, resembling an

open-ended ring. The topology is that of a straight line, with

nodes represented as points off the straight line, yet connected

to it. As the data travels along the cable, each node checks

and retrieves data as appropriate.

See also ring network, star network.

byte A unit of measurement of data storage capacity. A byte

consists of 8 bits.

15


CAD An acronym for computer-aided design. The process of using

a computer system to assist in the development of engineering

and/or architectural drawings.

callout A term referring to a short quote taken from the body of the

copy and printed large in the column, often blocked off from

the body copy with ruled lines designed to entice the reader

to read the body copy.

CAM An acronym for computer-assisted manufacture.

caption A term referring to a title attached to a graphic which can be

placed alongside, above or below the graphic. Used to relate

graphic work to the rest of the publication.

CASEWHERE A control structure in which the decision as to which of a

group of statements or instructions is to be executed depends

upon the value of the selection variable. Only one of the

possible alternatives is executed in any pass.

Compare with IF-THEN-ELSE

cathode ray tube The picture tube in a monitor or VDU.

CD ROM Acronym for compact disk read only memory. A medium for

storing digital data based on the technology of the compact

disk audio disk.

cel An individual still image to be used in an animation

sequence. Refers to traditional hand-drawn images on

separate sheets of celluloid — hence cel.

Compare with cell.

cel-based animation The method of producing animation by the creation of a

sequence of individual still images, each produced on a

separate cel.

Compare with path-based animation.

cel buffer A synonym for frame buffer.

cell (1) In a spreadsheet, the intersection of a row and a column.

See also address (2).

(2) The smallest physical storage unit of a computer’s memory.

Each cell has a specific storage capacity — usually a byte or a

word.

See also location.

C

16

Glossary of Terms

cell address See address (2).

cell pointer A special cursor that designates the cell in a spreadsheet into

which the entered information will be placed.

central processing unit Abbreviated to CPU. The CPU retrieves, decodes, interprets

and executes instructions. The CPU, which is incorporated in

an integrated circuit, can be described as comprising the control

unit, arithmetic and logic unit and temporary memory. The

temporary memory can be described as consisting of registers

and the accumulator.

centre tab A tab marker around which any text entered is centred.

See also decimal tab, left tab, right tab.

character The smallest unit of data that people normally handle. The

individual letters, numerals and symbols which go to make up

items of data.

character graphics A method of generating graphic images by the placement of

individual characters in groups. When viewed from a distance

the eye perceives a picture.

character printer An output device which produces fully formed characters

contained on a ball, wheel, chain or drum.

Compare with bit-mapped printer.

chart Numeric data represented graphically in a variety of ways;

usually generated by an application program.

Types of charts typically include: bar (histogram), column

(stacked bar), line (continuous) and pie (sector).

chip A shortened form of silicon chip; an alternative name for

integrated circuit.

clipboard Usually a temporary file to hold a piece of text or graphics to

allow easy transfer between documents or applications.

clock speed The rate at which the internal oscillator (the system clock) in

the control unit of the CPU sends out electronic pulses to

synchronise its operations. Measured in hertz (Hz).

CNC Acronym for computerised numerical control.

coding The act of converting an algorithm which is expressed in a

human readable form to statements which are able to be

compiled or interpreted by software in a computer.

colour depth The number of bits per pixel stored in the frame buffer. An

indication of the number of possible colours available for

display at any one time.

17


colour register This is the section of memory that holds information as to

which colours in the total palette are currently available.

colour value The numerical value of the bit pattern stored in the frame

buffer to represent the colour to be used to draw that pixel. Is

sometimes used as the index into a colour look-up table.

column (1) A series of cells arranged vertically in a spreadsheet.

(2) A term used to describe the vertical divisions of a page.

Text is usually arranged in one or more columns, the width

and alignment of which determine the placement and width

of lines of text and graphics.

command A keystroke, series of keystrokes or a selection from a menu

which causes software to carry out a specific action.

command interpreter Part of the operating system that interprets the user’s

keystrokes and sends a message to the appropriate utility or

application program to execute the command.

COMMAND key One of the modifier keys which provides an alternative set of

signals generated by combining a press of the COMMAND

key with another.

See also modifier key.

command-driven A term often used to describe a software package that requires

the user to type in the commands needed to manipulate the

data.

Compare with menu-driven.

communications software A type of application program that enables a computer to

exchange data, files and commands with another computer.

compact disk See CD ROM.

read only memory

compilation The process of converting an entire source program written in

a high-level language into machine language before executing

any of the program.

compiler A complex program which carries out the process of

compilation.

Compare with interpreter.

component (of a system) One of the following which together make up a system:

hardware, software, data, processes and personnel.

composite video This system of sending information to a monitor relies on

having all the signals carried along one wire, as in a nomal

home video system. Compare with RGB.

18

Glossary of Terms

computer An electronic machine which can accept data as input, process

and store data and produce output, under the control of a

program.

computer operator A person who looks after computing resources in a large

computer installation. The person is technically

knowledgeable about the equipment as the tasks often

include preparing, starting up and running the computers and

peripheral devices.

computer system A configuration of hardware and software functioning

together, processing data to achieve a purpose.

See also components.

computer word See word.

computer-aided design See CAD.

computerised Abbreviated to CNC. A system in which equipment (such as

numerical control a lathe) is controlled by data generated in and transmitted

from a computer.

configuration A statement of the hardware components of a computer system

and the interconnection between them.

consolidated spreadsheet A spreadsheet which has as its major input data the output

from other spreadsheets. It normally contains links to other

spreadsheets.

See also spreadsheet.

CONTROL key One of the modifier keys which generates the signal for the

associated predefined control character when pressed in

conjunction with another key. Often represented on the key

cap by CTRL.


control The function of one of the logical elements of the computer

system. Control of the system may be carried out by any or all

of the hardware, software, procedures and personnel of the

system.

See also control unit.

control function That part of the CPU’s task which manages the sequence of

operations. It is carried out by the control unit.

control structure One of three basic structures (sequence, selection and repetition)

which control the logic flow of an algorithm or program.

19


control unit That part of the CPU which carries out selection and retrieval

of instructions from storage in sequence, interprets them and

initiates the required operation. It also contains the internal

oscillator.

See clock speed.

copyright The sole legal right to produce or reproduce a literary,

dramatic, musical or artistic work, now extended to include

software.

CPU Abbreviation for central processing unit.

cropping The process of removing unwanted parts of an image.

cross-fade The process by which the colour of a pixel is changed gradually

from its original colour to a new colour. The total intensity of

the pixel usually remains constant during the change.

CRT Abbreviation for cathode ray tube.

cursor A movable symbol on a screen that indicates where the next

action will occur.

cursor control The movement of the cursor to any point on the screen.

custom software Software that is specifically written for a customer and is not

mass-produced.

cut-and-paste A block-action that defines a block of text or graphic and then

moves it to another place in a document or to another

document.

damping The process of modifying the magnitude of the response of acontrol system.

DASD Abbreviation for direct access storage device.

data The plural of datum. Data is often used as a collective nounaccompanied by a singular verb.

Anything with which the computer can work. There areseveral types of data: text, integers, real numbers, etc. Whendata is processed, and meaning is attached to the result, it iscalled information.

D

20

Glossary of Terms

data bias Bias which a user of information may apply based only on thedata stored in a database. Since the decision to include a recordin the database is founded on a limited number of conditionsand the amount of information is restricted by the number offields in a record, an unrecognised bias may be built in to allinformation obtained from that database, eg data about anindividual stored in a telephone directory is biased since onlythose people with a listed telephone number are included.

data bus The communications line that carries data between differentlocations in a computer.

Compare with address bus.

data communication The process of sending digitally coded data from onecomputer to another.

data compression A process by which the physical space required for data isreduced. Several techniques are used depending upon thetype of data which has to be compressed. Most commonlyused with graphic data.

data dependence Data dependence exists when the system software is

dependent on control by the application software for the way

in which the physical records are written to the storage medium.

Compare with data independence.

data dictionary A comprehensive description of each field in the database.

This commonly includes: field name, number of characters

(field width), data type, number of decimal places (if

applicable) and a description of the purpose of each field.

See also analysis.

data flow diagram A diagram which shows the logical flow of data through an

organisation (system) or subsystem.

See also analysis.

data hierarchy The classification of data order, eg from the lowest to the

highest level: character, field, record, file and database.

data independence Data independence exists when the system software is

independent of control by the application software for the way

in which the physical records are written to the storage medium.

Compare with data dependence.

data integrity A term used when describing the reliability of the data. It

incorporates a statement of data accuracy (correctness),

correct entry of the data and timeliness (currency) of the data.

data processing The manipulation of data to produce information.

21


data redundancy Undesirable duplication of data within a database.

data security The protection of computer software and data from accidental

or unauthorised manipulation, destruction or theft.

data validation A check on entered data to ensure that it is of the correct data

type and that its value is sensible.

database An organised collection of data items which may be accessedby a database management system. The database may consist ofseveral linked files.

A database is an organised collection of records.

database administrator The person responsible for setting up and maintaining theintegrity and security of a database. An administrator alsohelps programmers and end-users to utilise the databaseproperly.

database management system Abbreviated to DBMS. The software system that builds,maintains and provides access to a database. It also providesdata dictionary facilities, file protection and security againstunauthorised use. There are three types of DBMS:hierarchical, network and relational.

See also file management system.

DBMS Abbreviation for database management system.

debugging The process of finding and eliminating logic and syntaxerrors in a program or algorithm.

decimal tab A tab marker around which numeric values are aligned on theunits digit column. Any embedded decimal point is alignedwith the position of the marker, the whole number partappears to the left of the marker and the fraction part appearsto the right of the marker.

See also centre tab, left tab, right tab.

decision block That portion of an algorithm or program code where adecision is made to choose one path or the other dependingon the value of a specified condition.

decision support system A part of a management information system that combinesdata with models and graphics to answer questions about thedata. It is used to enable managers to make better decisionsthrough having information in a more understandable form.

decision table A table created during the analysis phase of the systemdevelopment cycle showing possible decisions and theirresulting actions.

See also analysis.

22

Glossary of Terms

decision tree Similar to a decision table except that it is expressed as a tree.

See also analysis.

declarative language A classification of programming languages in which thelanguage constructs represent relations and the emphasis ison what will be the output of a program rather than on howthe output is achieved. A classification within the non-procedural languages.

Compare with procedural language.

default A setting which will be applied unless a user or operator

specifies a different setting. For example, a word processor which

automatically creates each new document with a left margin of

2.5 cm has a default setting of 2.5 cm for the left margin.

delta information This is ‘change’ information. For example to speed data

transfers, when a screen is being altered only the data that has

changed is transmitted. The information that describes the

difference between two screens is called the delta

information.

density (1) A loose measure of the compactness of packing of

magnetic particles on a magnetic storage medium, for example:

single, double and high density. The higher the density, the

greater the disk’s data storage capacity.

(2) A measurement of the quantity of data stored on a

magnetic tape, measured in characters per inch (cpi) or bytes

per inch (bpi).

design The fourth stage of the system development cycle in which

decisions are made on how the new system will be organised.

The plan of the new system includes the overall organisation

envisaged together with the detailed requirements of input,

processing and output. This preliminary stage is followed by

details of hardware to be purchased, software to be written or

purchased, and procedures to be followed. Finally the

required purchases are made.

desk checking Checking the validity of an algorithm by working through the

written version of the algorithm using test data.

developers Persons who takes part in the production of a computer-

based system. Examples of developers include analysts, project

leaders, programmers, technical writers etc.

development cycle See system development cycle.

digit Denotes a unit of counting. One of the individual symbols

used in a number system.

23


digital Refers to any system where data is stored in some form of

coded numeric quantities having a discrete set, as opposed to

a continuous range, of possible values.

Compare with analog.

digital computer A computer that carries out its tasks by working with

numbers in the form of binary coded electrical signals.

See also analog computer.

digitise The process of converting analog data into digital form.

digitiser A device which converts analog data into digital form.

direct access Also called random access. A form of data access which

allows a record to be accessed without accessing the previous

record.

Compare with sequential access.

direct access storage device Abbreviated to DASD. Any secondary storage device on

which the data may be accessed in any order.

direct memory access An arrangement whereby data can be transferred between a

peripheral device and memory without requiring the CPU to

move the data.

directory A collection of pointers to where the data on the disk are

stored. A directory is often stored as a file. Analogous to the

table of contents in a book.

disk A circular piece of metal or plastic, coated with a thin layer of

magnetic material on which electronically transmitted data

may be stored.

See also floppy disk, hard disk.

disk drive A device that writes data to, or reads data from, a magnetic

disk. It contains a mechanism for spinning the disk and for

moving read/write heads over the surface of the disk.

diskette See floppy disk.

distorting See warping.

distributed data A processing system that uses a mainframe computer for

processing system database storage and large-scale processing, while minicomputers

or personal computers are used for local processing.

24

Glossary of Terms

distributed database A database on a network where each computer holds part of the

database. All parts of the database can be accessed by any

computer on the network. This allows a higher degree of data

security than if stored on one device, and by storing relevant

data locally gives faster access to the data.

dithering The representation of a colour not available in the existing

palette by the use of a pattern of varying colours where the eye

performs the averaging to produce the required colour.

documentation A written description of a software package, the hardware

configuration, the tasks it can perform and the way in which it

is used.

In a program, documentation is an explanation of the logic

and program statements.

dot matrix A type of printer in which the characters are formed by a

pattern of dots imprinted on the paper.

down time The time during which a computer is out of operation for

maintenance or repair.

download The action of the user’s computer receiving a file from another

(remote) computer.

Compare with upload.

drop cap An oversized first letter used to emphasise the first sentence

in a new section of a document.

drop shadow A term referring to an attention-getting three-dimensional

effect created by placing a graphic in a box with a filled box

behind which gives a shadow effect.

dumb terminal A terminal that carries out no local processing of the software.

It transmits characters typed at the keyboard and displays

information received on the screen.

dump A debugging technique in which the contents of all or part of

a computer’s memory are printed, or copied to secondary

storage. The output is known as the dump.

Dvorak A keyboard layout named after its designer, August Dvorak. It

was designed to enhance the speed and ease of typing by

placing the most frequently used keys on the home row under

the stronger fingers.

Compare with QWERTY.

25


EBCDIC Acronym for extended binary coded decimal interchange code.Pronounced ebb-see-dik. An eight-bit code for therepresentation of characters within a computer.

Compare with ASCII.

EBNF Abbreviation for extended Backus-Naur form.

In this extended form the following symbols are used:

= ‘is defined as’

‘or’ indicates a choice betweenalternatives

terminal symbol is used as a written (may be a symbolenclosed in quotation marks or areserved word written in upper case)

[ ] indicate an optional part of a definition

{ } indicate a possible repetition (0 or moretimes)

( ) used to group elements together

Example

Identifier = <Letter> { <Letter> <Digit> }

Interpretation

An Identfifier is defined to be a Letter followed by one ormore Letters or Digits.

Letter is a non-terminal symbol and is defined elsewhere, andDigit is another non-terminal symbol defined elsewhere.

See also BNF, Backus-Naur form, extended Backus-Naur form,railroad diagrams.

edit The process of changing or deleting data usually in the formof text.

Compare with proofreading.

editor A utility program which allows the user to edit data. Theeditor is usually designed to operate on data of a particulartype.

See text editor.

E

26

Glossary of Terms

27


effector Synonym for actuator.

EFT Abbreviation for electronic funds transfer. EFT is the use ofdata communication to transfer money between accounts.

EFTPOS Acronym for electronic funds transfer at the point of sale.EFTPOS is the use of data communication to allow thetransfer of money from the customer’s account to the firm’saccount by inserting a magnetic-striped plastic cardcontaining account details and keying in a personalidentification number (PIN).

electronic bulletin board A computerised version of a bulletin board that allows usersto post messages for other users, as well as a storage place forfiles which may be downloaded.

electronic funds transfer See EFT.

electronic funds transfer See EFTPOS.at the point of sale

electronic mail The use of data communication to send letters, documents andmessages between users.

electronic spreadsheet See spreadsheet.

embedded print code A code placed in a word-processed document to control theoutput. Often this code is visible on the monitor, but will itselfnot be printed.

emulator A program that allows a computer to execute the machine codeinstructions of another computer of a different design.

encode The process of changing information into a coded form.

encryption A means of improving security in data communication inwhich characters in the data are systematically changed torender them unreadable by any who do not possess the key.

end users People who use the computer system. They are usuallyemployees and customers.

environment The elements outside a computer system which affect thatsystem.

equity The concept of fairness and impartiality to which all personsshould be entitled as a right.

ergonomics The study of the relationship between people and theirworking environment.

error trapping The process of including code within a program to handleerrors which arise during execution.

ESC key ESCape key. One of the modifier keys which provides analternative set of signals generated by combining a press of theESC key with another. The signal generated by the ESC keyon its own is often used to terminate a running process.

See modifier key.

ethics A set of moral principles accepted by society as a standardagainst which individual behaviour can be judged.

expert system A computer program, based on various artificial intelligencetechniques, performing a specialised task at the level of ahuman expert. An expert system is often partitioned into aknowledge base, an inference engine, and (possibly) anexplanation system.

expert system shell A general purpose expert system containing reasoningmechanisms and a skeletal knowledge base into which a usercan inject specialised knowledge.

extended Backus-Naur form An extended and modified form of the BNF metalanguagefor the definition of the syntax of a programming language.Abbreviated to EBNF.

See also BNF, Backus-Naur form, EBNF, railroad diagrams.

extended binary coded See EBCDIC.decimal interchange code

external storage See secondary storage/memory.

feasibility study An activity carried out during the system development cycle,

usually on completion of the requirements definition stage.

The nature of the problem is clearly described and

recommendations are made to management as to whether the

proposed solution is practicable.

feedback The return of some part of output to be used as input in a

closed loop computer-controlled system.

fetch-execute cycle The cycle of events which a computer carries out to obey an

instruction. During the fetch part of the cycle the address of

the next instruction is used to access the memory and the

contents of that location are placed into a register. During the

execution part of the cycle the instruction in the register is

decoded and carried out.

F

28

Glossary of Terms

fibre optics The transmission of digital data as a series of light pulsesthrough an optical fibre.

field A subdivision of a record containing a specified piece of data.Each field is identified by its fieldname.

file A block of data comprising a related set of records that may bewritten to a storage device. A file may be made up of records,fields, words, bytes, characters or bits.

file conversion filter A program that translates the form of the data and associatedformat information stored in a file created by one applicationinto a form that can be meaningfully interpreted by anotherapplication.

file management system Software that allows the organisation, maintenance, storageand retrieval of files.

See also database management system.

file transfer protocol A set of agreed procedures for the transfer of a file from onecomputer system to another. Abbreviated to FTP.

firmware Instructions, often part of the operating system of thecomputer, that are stored in ROM.

fixed point representation The internal representation of numbers in which eachnumber is stored as a single set of digits. The point whichseparates the integer part from the fraction part is in a fixedposition within the set. Compared with floating pointrepresentation, this method limits the range of numbers thecomputer can manipulate, but the operation is relativelyfaster.

flag A variable used in a program (usualy in the development ordebugging stages) to indicate the result of a process, or thatthe process was executed.

flat file A type of database where all the data is contained in one file.

floating point representation The internal representation of numbers in which eachnumber is stored as two sets of digits, one holding themantissa and the other holding the exponent. The value ofthe exponent causes the decimal (binary) point to float untilit rests in the final, correct place. Compared with fixed pointrepresentation, this method allows a much wider range ofnumbers that the computer can manipulate, but the operationis relatively slower.

floppy disk Also known as a diskette. A disk made of flexible plastic andcovered with iron oxide particles. Generally used with amicrocomputer. The common sizes of floppy disks are 9 cm(3 1⁄2") or 13 cm (5 1⁄4") diameter.

29


flowchart A pictorial method of describing an algorithm in which thevarious steps are represented by symbols. For details seeMethods of Algorithm Description (2nd ed).

font In typography, the word is used to describe all the charactersin a tray of type that possess the same type face, type size, typestyle and stroke weight. For example:

Helvetica 10 point normal bold,

Times 12 point italic normal.

Now, in common computer usage, a font is generally taken tomean the name of the type face only.

footer A section of a document placed below the bottom margin of adocument. Commonly used to contain information requiredon each page of a document.

Compare with header.

footnote Material placed at the bottom of a page to comment on oramplify the material in the body text without interrupting theflow. The footnote and the material to which it refers areusually designated with matching numbers or symbols so thatthe footnote is noted as the text is read.

form letter A generalised document designed to be sent to a number ofrecipients. Information to be sent to all recipients is includedin the document. Information which is to differ on each letteris represented by a place holder.

See mail merge.

form view A layout in which a single record is displayed as though itwere contained on a paper form.

Compare with report view.

format (1) The organisation of text to improve its appearance and/orreadability. Formatting is carried out on the document byvarying such settings as margin width, paragraph indentation,margin justification, character size and spacing, line spacing etc.

(2) The process by which a disk is prepared to receive data.This involves the magnetic division of the disk surface intotracks and sectors.

formula (1) A combination of spreadsheet values, functions andconstants.

(2) A mathematical equation within a spreadsheet cell whichmay include operators and/or functions.

forward chaining The process of determining a conclusion from a given set offacts in an expert system.

Compare with backward chaining.

30

Glossary of Terms

frame A component of output in graphics or teaching packagesintended to be displayed as an entity to the screen. Rapiddisplay in sequence of a number of frames can produceanimation. Also referred to as a cel in graphics applications.

See cel-based animation.

frame buffer A section of memory used to store the data for the currentimage being displayed.

front end processor In large computer systems, a special-purpose computer used torelieve the central computer of some tasks. Often used to pre-process data before transmitting the data to an applicationrunning on the central computer.

FTP Abbreviation for file transfer protocol.

full-duplex mode A mode of communication between computers in which bothcomputers can transmit to each other at the same time.

Compare with half-duplex mode, simplex mode.

function A predefined set of operations which returns a value. Built-infunctions are those provided by the application software. In aprogramming language a function is a procedure (or subroutine)which returns a value. Most programming languageimplementations provide libraries of standard functions.

Compare with procedure.

function chart A hierarchical chart showing the relationship betweenmodules in a program. Also known as a hierarchy chart.

fuzzy logic A branch of logic designed specifically to support humanreasoning by allowing such linguistic labels as ‘fairly’ and‘very’ so that statements may be made with varying degrees ofcertainty and precision. In traditional logic a relation mayhave one of only two values (true or false). Fuzzy logic allowsintermediate values with appropriate probabilities.

31


Gantt chart A chart showing timelines for different stages of a systems

development project.

GIF Acronym for graphical interchange format which is a

standard format for the storage of graphic data to facilitate its

transfer between different graphics applications across a

network.

gigabyte 230 bytes (ie 1 073 741 824 bytes); approximately one billionbytes.

global change A change which affects the relevant parts of an entiredocument.

global search and replace Locating a specific string of characters and replacing it withanother for all occurrences of that string throughout theentire document.

gradient fill The process of filling an area of a computer image by asmooth variation of colours along a particular direction usingthe colour defined at each end of the pattern.

grammar checker An application program to check both grammar and style inword-processed documents. Suggestions are made forreplacements, and the readability of the document can bemeasured on a number of standard scales. Features present inthe program include checking for word duplication,homophones, overuse of words, punctuation errors andoverlong sentences.

graph See chart.

graphic A pictorial representation of data, generated by computersoftware.

grid The underlying structure of a page layout consisting of linesthat appear on the screen but not on the printed material. Itensures consistent alignment of margins, headers, footers, textand graphics.

guarded loop An alternative name for a repetition structure represented as aWHILE–DO construct in which the termination condition istested before the loop body is entered. The body of such aloop may never be executed in a particular run of a program.

Compare with unguarded loop

gutter A space on the inside edge of the page, additional to themargin, provided for binding.

G

32

Glossary of Terms

half-duplex mode A mode of communication between computers in which each

computer is capable of transmitting and receiving data in

either direction, but not both directions simultaneously.

Compare with full-duplex mode, simplex mode.

handshaking The exchange, in data communication, of prearranged signals

defining a protocol between two computers.

hard copy Computer output in a printed form. Includes output produced

by printers and plotters on some form of physical material such

as paper.

Compare with soft copy.

hard disk A type of disk in which the platters are made from metal and

the mechanism is sealed inside a container.

See disk.

hardware The physical units that make up a computer or any device

working with the computer.

Compare with software.

header A section of a document placed above the top margin of a

page. Usually contains information which identifies the

document or document part which needs to be repeated on

every page.

heading A label used to identify a particular block of cells in a

spreadsheet.

heuristic A rule of thumb or a technique based on experience and for

which our knowledge is incomplete. A heuristic rule works

with useful regularity but not necessarily all the time.

hexadecimal A number system that uses sixteen as its base. Because it

requires sixteen symbols, the letters A to F are used as digits

to represent the decimal numbers 10 to 15.

hierarchical database A database in which data is organised in a series of levels, in a

top-down structure consisting of nodes and branches. Each

node can have many branches but each lower level node

(child) is linked to only one higher level node (parent).

The database can only be searched from the root and only

one data path exists to a particular record.

See also network database, relational database.

H

33


high-level language A computer programming language in which each instruction

or statement corresponds to several machine code instructions.

High-level languages allow users to write in a notation with

which they are relatively familiar.

See also declarative language, procedural language.

Compare with low-level language.

HLS A representation of the colour appearing in an image bystating the levels of the measures hue, luminance andsaturation.

See also RGB.

horizontal rules Horizontal lines in a document used to separate topics withina column, to draw attention to callouts and subheads, whichcan be used to divide long blocks of text.

host computer The main computer in a network which provides facilities toother computers or terminals through communicationchannels.

host system A computer system which provides facilities to users atremote sites through communication channels.

hypermedia A term used to describe a combination of media containinginformation organised in such a way that it is possible tonavigate, simply, between the components of the informationirrespective of the particular medium on which thatinformation is stored.

hypertext A term used to describe text presented in a way that supportsdirect, intuitive navigation between elements of the text orother information which amplifies or illustrates the concept.The provision of ‘hot spots’ within the text which, whenclicked, present the user with additional information is oneexample of a hypertext feature.

34

Glossary of Terms

35


I/O Abbreviation for input/output. Often used to refer to

peripheral devices which may act either as an input device,

output device or both.

IC Abbreviation for integrated circuit.

identifier The name associated with an object such as a constant,variable, function or procedure in a program. Usually refers tothe name given by a programmer to an item in a programwhich represents a specific location in the computer’s memory.

IF-THEN-ELSE A control structure in which the decision as to which of a pairof statements or instructions is to be executed depends uponthe truth or falsity of a condition. Only one of the possiblealternatives is executed in any pass.

Compare with CASEWHERE.

implementation The fifth stage of the system development cycle is fully titledimplementation and testing. In this phase, users begin touse the new system, the performance of which is tested againstthe design specifications.

incremental compilation The process by which an interpreter automatically compiles asection of high-level language code which is frequently used inthe program, rather than repeatedly interpreting the relevantintermediate code, whilst still interpreting the remainingintermediate code.

See independent compilation, interpreter.Compare with compilation.

independent compilation A process by which individual modules of a large program arecompiled without the need to compile the entire program. Thisprocess allows only those modules which are changed duringdevelopment to be recompiled. All necessary compiled units arelater collected together by the linker before execution.Individual program units can be compiled without informationabout any other program units, eg the language C allowsindependent compilation. If there is a need to carry outinterface checking between the program units (the units to becompiled are not independent), the process is referred to asseperate compilation, eg Modula-2 allows seperate compilation.

inference engine The section of an expert system program that contains thelogic processing functions.

See expert system.

I

information Results from the processing of data. Information is derivedfrom the assembly, analysis or summary of data into ameaningful form.

information system The name given to all the operations and procedures (steps)involved in processing data.

input The process of transferring data or program instructions fromthe environment into the computer’s memory using someperipheral device. Sometimes used to denote the data itself,sometimes to denote the signal applied to a circuit or device.

insert mode An editing mode in which, after the cursor has beenpositioned, characters may be entered normally, whereupon alltext to the right of the cursor is progressively moved furtherto the right to provide space for the new characters.

Compare with overwrite/overstrike mode.

insertion sort A form of sorting by dividing the data structure into a sortedpart and an unsorted part, taking each element in theunsorted part in turn, finding its correct position in the sortedpart and inserting it there, thus increasing the size of thesorted part and decreasing the size of the unsorted part.

Compare with bubble sort, selection sort.

instruction A coded command or commands to a computer to perform acertain task.

integer One of the (infinite) set of the positive and negative wholenumbers including zero. In any computer application therange of allowable values is determined by the way in whichthe hardware represents an integer. Typical ranges are from– 32768 to +32767 if the system uses 16 bits and two’scomplement.

Compare with real number.

integrated circuit A circuit in which all the components are formed on a singlepiece of semi-conductor material (the silicon chip).Computers using integrated circuits are said to be thirdgeneration, as compared with first generation machines usingthermionic valves and second generation machines usingtransistors.

integrated package A software package that contains two or more applicationprograms, together with procedures to access themindividually and to permit a measure of interchange of databetween them.

36

Glossary of Terms

intelligent robot A robot which achieves an action that would be consideredintelligent if performed by a human. The robot is controlledby an intelligent system which enables the robot to interactwith the physical world based upon its perception of thatworld as determined by inputs from its sensors.

intelligent system A system that receives data from the environment throughone of a range of input devices, reacts to that data andproduces what humans would consider an intelligentresponse.

interactive processing A term used to describe the procedure in which the userinteracts with an executing program (an interactive program)whereby data may be entered, the program controlled, andresponses given to program requests. Common examplesinclude airline and theatre reservations programs.

Compare with batch processing.

interface A term used to refer to the paths of data transfer andassociated control circuitry providing the connection betweenthe computer and its peripheral devices.

It may be used more generally to refer to the connectionbetween any two units of hardware.

In its most general form it refers to the controls, screen layoutand allowable actions by which the user communicates withthe computer system.

interlacing The method used by television to display an image bygenerating alternate lines of the picture in two passes, aimedat improving the image. The two passes are called fields. Themethod was designed to reduce the flicker caused by therefresh rate of broadcast television; however, interlacing canactually cause flicker if adjacent lines contain distinctlydifferent information. Most computer display screens are non-interlaced.

interpreter A translator program that translates one line at a time of the

high-level source code into a low-level object code, whereupon

the computer executes that line before the next line is

translated.

Compare with assembler, compiler, translator.

iteration See looping.

37


jaggies The staircase roughness of oblique lines and polygon edges in

computer images caused by the underlying squareness of a

pixel.

See anti-aliasing.

joystick An analog input device able to detect relative movements in

two dimensions and transmit appropriate signals to the

computer.

justification The process of positioning words so that vertical alignments

are produced on either or both ends of lines of text. The

terms used are: left, right and full justification.

K Kilo — 1024 (bytes) in computer terms, rather than 1000.

Kb Abbreviation for kilobyte.

kerning The typesetting practice of closing the horizontal space

between some letter combinations to achieve a better fit.

Compare with leading.

key (1) A character or group of characters used to identify a

unique record in a database. The key is composed of one or

more fields from the record. Also known as primary key.

Examples of primary keys could be ID number, part number,

payroll number, etc.

See also secondary key.

(2) The name given to the switches on a keyboard.

key to disk A term used to describe both the process, and the device

used, to enable data to be entered directly from the keyboard

to a disk without using the main computer system.

key to tape A term used to describe both the process, and the device

used, to enable data to be entered directly from the keyboard

to a magnetic tape without using the main computer system.

K

J

38

Glossary of Terms

39


keyboard An input device for converting the depression of keys

(keystrokes) into electrical signals which are (usually)

interpreted as characters represented in ASCII by the

computer. There are several different arrangements of keys

on the keyboard.

See also Dvorak and QWERTY.

kilobyte 210bytes (ie 1024 bytes), approximately one thousand bytes.

Abbreviated to Kb or Kbyte.

knowledge base A database used in artificial intelligence applications that

consists of facts, inferences and rules needed to solve a

problem.

knowledge engineering The art of designing and building an expert system. In

particular, collecting knowledge and heuristics from human

experts in their area of speciality and assembling them into a

knowledge base or expert system.

label (1) One of the data types used in a spreadsheet. It is textentered in a cell to provide some explanation, thus facilitatingthe understanding of the spreadsheet.

See also value.

(2) In programming, it can refer to a number or text used toidentify an instruction in a program, or to identify an entrypoint to a particular line or instruction in a program orsubroutine.

LAN An acronym for local area network.

layout (1) The general form of a document, frame, report or screen.Usually includes definitions of the characteristics of eachcomponent.

(2) The action of placing the components of a document,frame, report or screen in position and adjusting theirpositions and characteristics to produce an effective design.

leading A term used to describe the amount of space separating oneline of type from the line above and below. It is the standarddistance between base lines. Also known as vertical spacing.

Compare with kerning.

L

leased lines Special high-speed telephone lines that are leased from atelephone company to transmit data between computers.

left tab A tab marker against which any text entered appears to theright of the tab marker with the left-most character alignedwith the tab marker.

See also centre tab, decimal tab, right tab.

light pen A photo-electric device used as an adjunct to a CRT screen.The operator is able to pass the pen over the surface of thescreen, and, under program control, to create, manipulate andmodify images. The pen responds to the CRT’s electronbeam.

line editor A type of text editor that allows the user to make changes to adocument on the current line.

See also text editor.

linear search An algorithm used to search structured data. The data neednot be ordered. The algorithm compares each item of datawith the target until either the target is found or it isdetermined that the target is not present.

See searching.

Compare with binary search.

linker A system utility used to join compiled modules to form an

executable program.

local area network A network of computers designed to provide facilities for

inter-user communication within a single building or site.

Abbreviated to LAN.

Compare with wide area network.

location A synonym for address.

logic error An error in the logic of the program which causes incorrect

actions to be taken. Can normally only be detected by the

programmer during the testing and debugging of the

program when carefully selected test data is used as input to

see that the program generates the known result.

Compare with run-time error, syntax error.

logical element One of the five conceptual components of a computer system

as they appear to a user. These are: input, output, processing,

storage and control.

logical operand An element which evaluates to one of the two values true or

false.

See Boolean algebra.

40

Glossary of Terms

logical operator An operator which can be used with logical operands

(eg AND, OR, NOT).

logical process A process involving the use of Boolean algebra in which the

results can be represented in a truth table.

logical record The conceptual appearance (user’s view) of a set of related

data treated as a single record.

Compare with physical record.

LOGO A programming language developed by Seymour Papert

incorporating instructions for the control of a physical or

symbolic (screen) ‘turtle’.

logo A symbolic design that may include both a graphic and text

intended to represent a company or organisation.

logoff/logout The process a user employs to disconnect from a network.

logon/login The process a user employs to connect to a network.

looping See repetition.

low-level language A computer programming language in which each instruction

corresponds to a single machine code equivalent.

Compare with high-level language.

machine code/language A language consisting of binary-coded instructions which canbe understood and executed by the computer. A machinelanguage is specific to the CPU of a particular computer.

machine readable A term often applied to characters or data. It denotes theability of some input device to read suitably preparedcharacters or data into the computer’s memory.

macro A term generally used to denote a routine, which is a set ofinstructions or a list of keyboard commands, stored in a file,that can be executed by entering a few keys from thekeyboard. Macros are used to save time and reduce thechance of keyboard errors in the execution of complicated orlengthy routines within an application.

M

41


magnetic ink Abbreviated to MICR. Reading characters into the computer’s character recognition memory with a character reader that uses appropriate software

to read the characters that have been printed in magnetisedmetallic ink.

mail-merge A process by which the contents of one document arecombined with sets of different information (names,addresses, etc) sourced from another document or from adatabase to produce form letters.

main memory See primary storage.

mainframe A computer mainly used by large organisations. It is capableof handling a large number of programs or userssimultaneously, processing very large amounts of data at veryhigh speeds. Access to mainframe computers is by the use ofterminals.

Compare with microcomputer.

mainline The main controlling sequence of instructions of a computerprogram. The program code excluding subroutines, definedprocedures and external function calls.

maintainer The person carrying out the task of maintaining an existingcomputer-based system, its hardware and software.

See operation and evaluation.

maintenance See operation and evaluation.

manager A person with the responsibility to oversee a specific sectionof a company or a particular activity.

• The systems manager oversees the activities in the systemsanalysis and design areas.

• The programming manager oversees the activities of theprogrammers.

• The project manager oversees the activities of the systemsand programming managers.

• The operations manager oversees the operational aspectsof the entire group including scheduling, maintenance andoperation of the equipment.

margin The distance between the boundaries of a page and the areawhere the text and graphics appear.

An imaginary line marking the boundary between the marginand the body of the page.

masking A filter operation carried out on a byte or word, in order tomodify or identify part of it. By using logical operator such as‘OR’ or ‘NOT’, mask can suppress bits in the data.

42

Glossary of Terms

master A layout showing the relative size and positions ofcomponents on a page used as a guide for the layout of everypage of the document.

Mb Abbreviation for megabyte.

medium The particular material on which data is recorded.

megabyte 220bytes (ie 1 048 576 bytes), approximately one million bytes.Abbreviated to Mb or Mbyte.

megahertz One million cycles per second. This unit is frequently used tocompare the clock speeds of CPUs. Abbreviated to MHz.

memory See store. The term is often reserved for describing theprimary storage of the computer.

menu-driven A term used to describe software packages that require theuser to enter commands through menu selections.

MHz Abbreviation for megahertz.

MICR See magnetic ink character recognition.

microchip See microprocessor.

microcomputer A self-contained computer that uses a microprocessor as itsCPU.

Compare with mainframe.

microprocessor A single silicon chip which contains some memory and

features which enable it to be programmed to perform a

range of basic logical processes, thus providing a complete (or,

in some cases, reduced) instruction set for a CPU.

MIDI Abbreviation for musical instrument digital interface. A

standard interface to connect musical instruments to a

microcomputer.

minicomputer A term used as a computer classification for a machine

somewhere between a microcomputer and a mainframe in size

and in performance.

MIPS An acronym for millions of instructions per second. This unit

is frequently used to compare processing speeds of computers.

MNP-5 An abbreviation for microcomputer networking protocol

which is a hardware data compression and decompression

technique.

model A term used with spreadsheets to represent or simulate, in

mathematical form, a real-life system, activity or process.

43


modem Contraction of modulator-demodulator. A device enablingthe transmission of data from one computer to another. Amodulator converts digital signals from the transmittingcomputer into analog signals suitable for transmission overtelephone lines. A demodulator converts the analog signalsback to digital signals at the receiving end.

modifier key A name given to any one of a set of keys which can each beused in conjunction with the normal alphanumeric keys togenerate an alternative set of signals.

See also ALT key, CONTROL key, COMMAND key, ESC key,OPTION key, SHIFT key.

modular A term used to describe a structured program or algorithmcomprising a number of modules.

module A module performs a complete portion of a larger task andconsists of one or more subprograms. It can pass data to andfrom other modules.

monitor A television-like device used to display images generated bythe computer.

morphing The process of producing a sequence of computer imagesanimating the smooth transformation from one image toanother, especially in terms of the shape of objects.

See also warping.

mouse A mechanical or optical input device used to move a pointeron a screen.

multi-way selection A control structure in which a choice between two or morealternatives is made based upon the value of an expression.Usually implemented as a CASEWHERE structure.

Compare with binary selection.

natural language A spoken or written language (eg English) governed by setsof rules and conventions sufficiently complex and subtle forthere to be frequent ambiguity in syntax and meaning.

natural language processing An application of artificial intelligence directed at acceptinginput and/or providing output in the form of a naturallanguage.

N

44

Glossary of Terms

network A system that allows a number of computers and their

peripheral devices to be connected over a distance.

network database A database in which data is organised as a series of nodes

linked by branches. Each node can have many branches and

each lower level node (child) may be linked to more than one

higher level node (parent). More than one data path can lead

to a particular record.

See also hierarchical database, relational database.

neural network A computer program which is designed for assigning data into

classes. The program consists of several layers, each

containing summing nodes. It calculates its output using the

weighted sum of its inputs. The program is trained on data

for which the appropriate classes are known, patterns are

extracted and this information is applied to new data to

detect specific patterns and hence to classify, automatically,

the new data. Neural networks form an area of investigation

in the field of artificial intelligence which attempts to model

human thinking.

node (1) The name given to each computer or device in a

communications network.

(2) A location in a database at which data is stored.

non-reproducible blue A shade of blue that will not normally reproduce in black and

white photography.

non-volatile memory Memory which does not lose its contents when the power to

the computer is turned off.

See also ROM.

Compare with volatile memory.

non-procedural language A programming language that requires programmers only to

specify what they want to do, without details of how to do it,

eg Prolog, query languages.

Compare with procedural language.

numeric keypad A section of a keyboard or a separate keyboard which contains

only those keys essential for the input of numeric data. It

usually contains the keys which generate the ten digits, the

four arithmetic operators, the = sign, the decimal point and a

key to indicate the end of the individual data item.

45


object code The machine code produced as a result of compiling a program

written in a higher level language (the source code); the code

which runs when loaded into the computer.

Compare with source code.

OCR (1) Abbreviation for optical character reader.

A hardware device used for optical character recognition.

(2) Abbreviation for optical character recognition.

The use of appropriate software to convert typewritten or

printed documents into electronic form suitable for

processing by a text editor.

octal A number system in which the base is eight and which uses

the eight digits 0…7.

off-line The peripheral device is in a state independent of the control

of the CPU.

on-line The peripheral device is in a state under the direct control of

the CPU.

operating system The software that supervises and controls system resources

such as the CPU, memory, storage devices and I/O devices; and

executes other (user-controlled) programs. The operating

system also manages the flow of data.

operation and evaluation The sixth and final stage of the system development cycle.

While the new system is in operation, evaluation of its

performance is carried out in all areas, including: response

time, processing time, remaining storage capacity, needs of

the user, needs of the organisation, emergence of any bugs or

programming inadequacies. Maintenance of the system is

then instituted whereby all required adjustments or

corrections are carried out as a result of the continuing

evaluation.

optical fibre A hair-thin flexible glass or plastic strand, through which

light can be transmitted, encased in light-reflecting cladding.

OPTION key One of the modifier keys which provides an alternative set of

signals generated by combining a press of the OPTION key

with another.


O

46

Glossary of Terms

organisation chart A diagram used to show the hierarchical structure of modules

in a large program. It may additionally show the major

connections between modules in terms of the data which has

to be passed.

orientation A term used to describe the direction in which an object is

facing.

originate mode The way in which the modem is operating — making the call.

This mode is characterised by the use of the higher of the two

frequencies used by a modem in full-duplex communications,

eg 1200/2400 Bps. The higher rate is used for originating the

data link.

Compare with answer mode.

outlining package An application package which allows the user to allocate levels

of importance to headings, sub-headings and blocks of text.

The lower level headings and text can be hidden so that the

larger structure of the full document can be viewed.

output (1) The process of transferring data or information from the

computer’s memory to the environment using some peripheral

device.

(2) The data or information produced on a peripheral device.

overwrite/overstrike mode An editing function in which the typed characters replace the

existing characters.

Compare with insert mode.

packet A group of binary digits containing data and control characters

which form part of a complete digital message. The size of

the packet can be up to 1 Kb. The control characters permit

the checking and correct re-assembling of the message.

See also packet switching.

packet switching The process of routing and transferring data in packets. The

packets may take different routes to the destination where

they will be correctly re-assembled. Originally developed for

security purposes.

See also X modem, Z modem.

P

47


pagination The process of breaking a document into separate pages.Page breaks may be generated automatically by the softwareor inserted manually by the user.

palette The set of colours available for selection to display at a pixel.

paradigm An overused jargon word which can be replaced by any of itssynonyms such as model.

parallel transmission A transmission process in which a number of data bits aretransmitted simultaneously, each bit along a separate channelor wire.

Compare with serial transmission.

parameter A value or variable passed to a function or procedure. It may beused to provide data to the function or procedure or to returndata from it.

In programming, parameters may be passed betweenprocedures or modules.

See also argument.

parity A characteristic of each transmitted character or group ofcharacters which is used to check the accuracy of the receiveditem. Even parity means that a valid item must consist of aneven number of bits which are set to ‘on’, while odd paritymeans that a valid item must consist of an odd number of bitsset to ‘on’.

parity bit An additional bit attached to the binary code for eachtransmitted character or group of characters for the purpose ofchecking the accuracy of the received item.

parse tree A tree data structure in which the nodes correspond tokeywords, symbols and statement elements as they areidentified by the parser during part of the compilationprocess. Applying syntax rules to the structure of theelements, as indicated by their position in the parse tree,enables syntax errors to be identified.

password A string of characters set by the user to protect againstunauthorised access to a computer or files.

paste The process by which a copy of the section of the screen thatwas cut or copied is inserted in a document at the currentscreen location.

path-based animation A method of animation in which the starting point, endpoint and the path to be followed by an object are defined.The software generates the object as it moves along thedefined path to represent the animation.

See also cel-based animation.

48

Glossary of Terms

49


pattern A description of the elements of a string.

pattern matching (search) Searching a series of one or more strings in order to find thosestrings with an identical pattern to the search string.

See also wildcard character.

peer checking A process whereby programmers not involved with theoriginal design are asked to check the logic of an algorithm.

peripheral device Any I/O device connected to the CPU of a computer.

permanent storage A storage device for data that is composed of a non-volatilestorage medium.

personnel One of the components of a computer-based system. Thepeople employed to work with that system.

physical record A record as written to the storage medium by the systemsoftware. A physical record can consist of a number of logicalrecords.

Compare with logical record.

PIN Acronym for personal identification number which is aunique number issued to a user to identify that person to anelectronic banking system.

piracy A euphemism for theft of intellectual property by the copyingor use of software to which the user has no legal right.

pixel Acronym for picture element. The smallest part of the screen,the appearance of which can be controlled by the computer.

pixel averaging The method of anti-aliasing where each pixel represents the

average of a number of colours which should be present in

the physical area covered by the pixel.

See anti-aliasing, jaggies.

pixel resolution See resolution.

PK ZIP A software data compression and decompression technique.

plotter An output device that uses pens to draw the image.

point size A measurement of the size of printed characters.

See type size.

polygon Any closed, plain figure with three or more straight sides.

populate (database) The action of adding records to a newly created database.

post-test The testing of a termination condition of a loop after the loop

body is entered. Usually implemented as a REPEAT-UNTIL

statement.

See also unguarded loop.

Compare with pre-test.

preprocessing The process of checking and editing input data to make sure

that it is in a suitable form for processing by the main program.

pre-test The testing of a termination condition of a loop before the

loop body is entered. Usually implemented as a WHILE-DO

statement.

See also guarded loop.

Compare with post-test.

presentation graphics Graphics software packages that present data and information

in a more understandable or dramatic form than analysis

graphics.

primary key See key (1).

primary storage/memory The part of the computer that temporarily holds data and

programs before and after they are processed by the ALU.

Primary storage is often called main memory, RAM, or even

just memory.

Compare with secondary storage.

printer An output device capable of converting electric signals to

physical impressions on paper.

problem definition See requirements definition.

procedural language A programming language that requires programmers to specify

a step-by-step process to tell the computer how to carry out a

task, eg BASIC, Pascal, COBOL, FORTRAN, C.

Compare with non-procedural language.

procedure (1) See subprogram.

(2) A set of agreed actions to be carried out to complete a

task.

process As a noun, this word has the normal English meaning. As a

transitive verb, it means to execute an instruction or series of

instructions.

processing The manipulation of data.

50

Glossary of Terms

program A sequence of instructions written in a programming language

that directs a computer’s actions.

See also software.

programming language A language used to create, store, recall and edit instructions

used to control the operation of a computer.

See also high-level language, low-level language.

proofreading Traditionally, checking that the type set for the printing press

matched that of the original manuscript. In modern usage it

includes a continuing process of checking documents during

their creation, interspersed with editing.

proportional spacing A method of spacing which ensures that the amount of space

used by each symbol varies according to the width of each

symbol to avoid excessive gaps between adjacent letters and to

allow flexibility in the justification of a line of text.

protocol A set of rules that governs the transmission of data between

computers.

prototyping The process of quickly developing a working version of a

program or application without the need to provide the

detailed coding to produce or link elements.

pseudocode One method of algorithm description involving the use of

English. Although similar in many respects to Pascal and

related high-level languages, it does not observe the same very

strict syntax rules. For details see Methods of Algorithm

Description (2nd ed).

query language The method of formulating queries in an information retrieval

system to retrieve data.

See also non-procedural language.

QWERTY A keyboard named after the first six letters of the second row.

Often referred to as a ‘standard’ typewriter keyboard.

Compare with Dvorak.

Q

51


railroad diagrams This is an alternative, graphical method used to define the

syntax of a programming language.

Rectangles are used to enclose non-terminal symbols. Circles

or rounded rectangles are used to enclose terminal symbols.

These elements are linked by paths to show all legal

combinations. By starting at the left-hand side of a diagram

and tracing any path in a forward direction to reach the right-

hand side of the diagram, a syntactically correct construct will

be covered.

(‘Railroad’ in this context means a branch in the diagram is

legal if it is treated as a set of points in a railroad layout and a

train can take the branch in a forward direction.)

Example:

See also BNF, Backus-Naur form, extended Backus-Naur form,

EBNF.

RAM See random access memory.

random access A synonym for direct access.

random access memory Abbreviated to RAM. It is the primary memory, and is used to

contain both data and instructions (programs) generated by the

user. Data may be read from or written to this type of

memory. Most technologies used for this memory make it a

volatile memory.

raster The means by which an image is built up on the screen of a

cathode ray tube. The image is formed from a pattern of

horizontal scanning lines (the raster scan) traced by the

electron beam.

read only memory Abbreviated to ROM. Memory with instructions and/or data

which are fixed at the time of production and cannot be

erased or changed. ROM is non-volatile memory.

R

52

Glossary of Terms

Letter

Digit

Letter

real number One of the (infinite) set of numbers which can be represented

as a ratio of two integers. In any computer application the

range of allowable values is determined by the way in which

the hardware represents a real number.

Compare with integer.

real-time processing The processing of data as they are transmitted to the

computer.

record A collection of facts about an entity in a database. A record

comprises one or more related fields.

register A group of fast access memory cells within the CPU. It is used

for the temporary storage of data or instructions.

See also accumulator.

relational database A database in which data is organised in a series of

relationships, or two-dimensional tables, where the columns

(attributes) represent data fields, and the rows (tuples)

represent records.

Linking of data between records in different files is done by

means of a key field.

See also hierarchical database, network database.

relative address See address (1).

relative cell address See address (2).

relay An electro-mechanical switch in which one current is used to

control another. It is one type of actuator in a computer-

controlled system.

remote database A database maintained on a host computer located at a

distance from the user’s site. Access is usually through

electronic communication.

rendering The process of producing a computer image — usually

reserved for the creation of images of three-dimensional

scenes by computer in which the image is enhanced by the

addition of surface colours and textures.

REPEAT-UNTIL A control structure in which the group of statements or

instruction within the body of the structure are executed until

the termination condition is true. The body of the structure is

executed at least once.

Compare with WHILE-DO.

repeater A device that receives, amplifies and re-directs broadcast

signals.

53


repetition In a computer program or algorithm repetition involves the

execution of one or more statements a number of times. The

repetition may be finite or infinite. One of the three basic

control structures. Also known as iteration.

See also WHILE-DO, REPEAT-UNTIL.

requirements definition The first stage of the system development cycle in which clear

and concise statements are made of what is required of the

computer-based system.

resolution A measurement of the clarity of an image. The common

units of measurement are:

printers: dots per inch (dpi);

screens: the total number of pixels that can be displayed

horizontally and vertically, eg 640 x 480.

response time (speed) The amount of time elapsing between the transmission of a

command and the receipt of some response from the

computer.

reverse A term used to describe headlines or short sentences

displayed in white type against a black background. Also

known as inverted text.

RGB When used in conjuction with monitors this is a system

where the information for the monitor is split into three

components: Red, Green and Blue. Each of these signals is

sent along a separate wire.

Compare with composite video, HLS.

right tab A tab marker against which any text entered appears to the

left of the tab marker with the right-most character aligned

with the tab marker.

See also centre tab, decimal tab, left tab.

ring network A communications network in which the topology is that of a

continuous circle, with nodes represented as points on the

circumference.

Messages between nodes must pass through all intervening

nodes on the ring.

See also bus network, star network.

54

Glossary of Terms

robot An articulated mechanism, together with any auxiliary

support devices, that is capable of autonomous motion. The

term originated from the Czech word robotnik meaning

‘forced labour’ and referred to artificial humans in Karel

Capek’s play ‘Rossum’s Universal Robots’. The term is now

most commonly applied to a multi-functional device, which

combines a computer-controlled system with sensors and

actuators, designed to carry out some predefined task with

minimal human intervention.

robotics A discipline lying across the border between artificial

intelligence and mechanical engineering which combines

elements of kinematics, statics, dynamics, trajectory planning,

programming and control theory.

ROM Abbreviation for read only memory.

row A series of cells placed horizontally in a spreadsheet.

ruler The line at the top or bottom of a word processing document

that displays dimension information and enables the user to

define the placement of items such as margins, tab stops and

columns.

A horizontal or vertical line which may be displayed on the

screen allowing the precise placement of screen elements.

rule (1) Lines used to separate one part of a publication from

another. Vertical rules are often used to separate columns,

particularly when non-justified type is used.

(2) A set of relations in an expert system which define the

action to be followed when the specified conditions are met.

run (an application) The process of causing an application to start. The command

given to initiate the execution of a compiled program.

run-time error An error which occurs when the object code is executed. It

may be the result of a logic error, an undefined arithmetic

operation such as division by zero, or an overflow error which

occurs when a result is computed which cannot be correctly

stored in the nominated memory location.

Compare with logic error, syntax error.

55


scan The process by which an input device systematically inspects

each element of a document and translates the data produced

by the inspection into signals which can be received and

stored by a computer. The input data may be in the form of a

bit map or ASCII characters depending upon the hardware

and software used.

scanned image The stored representation of an image produced by scanning.

schema An organised plan of the entire database showing how and

where the data is to be found, descriptions of the data, and

their logical relationships. The schema is produced by the

database designer and is maintained by the database

administrator.

screen The front or display surface of a monitor.

screen elements Headings, menus, user instructions, navigational tools, blocksof text and graphics which are placed together to form adisplay on a screen.

scroll Scrolling is a method of moving within a document. The usercan move forward, backward, left or right to see otherportions of a document which are not visible on the currentscreen. It is possible to move by one line or column, onescreen or a variable amount at a time, in the direction desired.

search and replace To examine each character in a document in order to discoverwhether it satisfies certain conditions. If these conditions aremet, the character (or string) may be replaced by anotherspecified character or string.

searching Examining data in order to find a data element (or elements)which satisfies certain criteria.

secondary key A field or combination of fields that is not necessarily uniqueto a record but applies to one or more records. Secondary keyscan be used to sort a group of records within a collection ofrecords identified by their primary key or to select a group ofrecords from those identified by the primary key.

See also key (1).

secondary storage/memory Storage provided on a peripheral device, eg hard drive, floppydisk, magnetic tape. Also known as backing store. Secondarystorage media are normally non-volatile.

Compare with primary storage.

S

56

Glossary of Terms

selection In a computer program or in an algorithm selection determineswhich particular step (from a set of steps) is to be executednext. A selection statement can be used to choose a specificpath dependent upon a condition. One of the three basiccontrol structures.

See also binary selection, multi-way selection.

selection (database) The process of identifying and temporarily abstracting agroup of records in which the contents of various fields in eachof the selected records match the values provided in thequery.

selection sort A form of sorting by dividing the data structure into a sorted

part and an unsorted part. The next largest (or smallest) item

in the unsorted part is found and placed in the next available

position of the sorted part. Thus the size of the sorted part is

increased and the size of the unsorted part is decreased.

Compare with bubble sort, insertion sort.

sensor Any device which converts input provided by theenvironment into a signal which can be communicated to acontrol program.

Compare with actuator.

sequence In a computer program or in an algorithm, sequence involves aset of simple steps which are to be executed one after theother. The steps are executed in the same order they arewritten. One of the three basic control structures.

sequential access A form of access in which data items are accessed one after

the other, usually in the order they were created.

serial transmission A form of data transmission in which the bits of each character

are transmitted sequentially, one at a time, over a single

channel or wire.

Compare with parallel transmission.

shadow mask A device which ensures that each screen dot is only energised

by an electron gun of its own colour of red, green or blue.

SHIFT key One of the modifier keys which provides an alternative set of

signals generated by combining a press of the SHIFT key

with another. Generates the upper case letters and the

characters shown as the upper character on each key cap.


57


signal A term used to describe the physical form in which data istransmitted, eg pulses of electricity in a wire, pulses of light inan optical fibre cable, or electromagnetic radiation from atransmitter.

silhouetting A technique which eliminates unimportant backgrounddetails in a graphic image. Also called masking.

simplex mode A mode of communication between computers which allowstransmission in one direction only.

Compare with full-duplex mode and half-duplex mode.

sink A term used to describe extra white space at the top of a pagethat forces the reader’s attention to the body copy below it.

soft copy Computer output displayed on a screen or in a physical formwhich can be transferred to another computer (eg on disk).

Compare with hard copy.

software A sequence of detailed instructions used to direct theoperation of a computer. Software is generally categorised aseither application software or system software which includesutility software.

Compare with hardware.

solenoid An electro-mechanical device in which an electrical currentcreates a magnetic field. Often used as an actuator whenoperating as a switch.

sorting Arranging items of data in a particular order.

See also bubble sort, insertion sort, selection sort.

source code The original high-level language program written by thecomputer programmer.

Also known as source program.

Compare with object code.

source program See source code.

speech recognition The process of converting voice input into signals and havingthe software match the input’s characteristics against knowncharacteristics in order to convert the voice input into datawhich the system can then use.

speech understanding The process of using data obtained from speech recognition toinstruct the computer to perform some task.

spline A smooth mathematical curve which passes through a smallnumber of given points.

See also Beziér curve.

58

Glossary of Terms

spreadsheet An application software package using a rectangular grid madeup of rows and columns; the intersection of a row and a columnis a cell. The spreadsheet can manipulate values, and the usercan specify interrelationships between the values. Theapplication can calculate results using formulas, functions andmacros.

star network A communications network in which there is one centralcoordinating node and distant nodes are connected alongcommunications lines which radiate as spokes from thecentral node.

See also bus network, ring network.

start bit A bit at the beginning of a character in asynchronouscommunication that signals the transmission of a character tothe receiving computer.

Compare with stop bit.

statement In programming, an expression or generalised instructionwritten in the language of the source program.

status line A line (or sometimes a bar) on the screen which supplies theuser with certain details relating to the application programcurrently in use, eg file name, key status, cursor position (suchas line, column, page).

stepping motor A motor which rotates a predetermined precise number oftimes each time a pulse of current is applied. Used as anactuator.

stepwise refinement An approach to problem solving where the problem is brokendown into successively smaller components until eachindividual component is easily solvable.

stop bit A bit at the end of a character in asynchronous communicationthat signals the end of the transmission of a character to thereceiving computer.

Compare with start bit.

storage A convenient synonym for store.

store Any device or medium which is capable of receiving data,

retaining it over a period of time, allowing it to be accessed

and retrieved when required. A store may be categorised as

primary or secondary, and as permanent or temporary. The

medium on which the data is stored may be classified as

volatile or non-volatile.

59


60

Glossary of Terms

storyboard An annotated sequence of rough drawings to represent a

possible sequence in a proposed application, animation

sequence or motion picture. The annotations provide general

directions to the creator as to how the components should

look and how each frame relates to its predecessor and

successor.

string A term often used to describe a sequence of characters treated

as a single entity.

stroke weight A measure of the thickness of the lines used to construct

characters, eg bold, normal. Bold is accomplished by

increasing the stroke weight.

structured programming A programming technique characterised by the whole being

broken down into small, independent modules, each of which

has a single entry and exit point.

See also top-down design.

structured walk through A review of an algorithm design. It entails using a pen and

paper to theoretically execute the design sequence in order to

verify that it faithfully carries out the required tasks before

coding takes place.

stub An incomplete procedure or function which has the same name

and interface as the final form but is much simpler. Usually

only contains an output statement to indicate that the

procedure or function was called, together with any essential

statements to ensure that related procedures and functions

can work correctly. Used in testing the implementation of a

program.

style (1) A set of rules that defines a form of language usage

acceptable for a particular targeted audience, eg legal,

educational, etc.

(2) See type style.

style checker An application program used in word processing. Moderngrammar checkers will carry out both grammar and languagestyle checking of a document.

See grammar checker.

subsystem A self-contained part of a system.

subprogram A self-contained section of programming code which can beincorporated into a complete program. A subprogram can beentered from any point in the main program and usuallyreturns to the instruction immediately following the branch tothe subprogram. Subprograms have only one entry and exitpoint. Subprograms are also known as procedures.

subroutine Synonym for subprogram.

synchronous A system of high speed data transmission in which clocks inboth receiving and transmitting terminals are used to ensurethat data is processed at the same rate.

Compare with asynchronous.

syntax The rules governing the way in which elements of aprogramming language may be combined to form legalstatements.

syntax diagram See railroad diagrams.

syntax error An error detected by the compiler when it is unable to matchitems in the source code eith legal syntactic entities in thatlanguage.

Compare with logic error, run-time error.

system A computer or computers, together with all relatedcomponents, including personnel, peripheral devices andsoftware, that work together to achieve some function.

system accounting The maintenance of records about the use of a system whichmay include such aspects as the amount of terminal time,CPU time and storage space consumed by particular users.

system development cycle The six stages of the system development cycle are:requirements definition, feasibility study, analysis, design,implementation and testing, operation and evaluation.

system software The files, utilities and resources that the computer needs torun properly.

Compare with application software.

system utility A utility program provided with the operating system.

systems analyst A person who develops a systems design to meet a new needor solve a problem in an existing situation and can adviseprogrammers by designing detailed algorithms.

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TAB The white space character which, when placed within a

document, causes the next item of text, number or graphic to

become aligned with the position determined by the next tab

stop.

tab stop Markers placed within a document to force the alignment of

items of text, numbers or graphics as they appear on successive

lines.

See centre tab, left tab, right tab, decimal tab.

table view A layout in which a number of records are displayed

simultaneously with their corresponding fields aligned in

columns. For large records not all fields can be displayed at

once.

tape drive An electronic device with a read/write head that transfers

data to and from magnetic tape.

telecommunications The technology of transmitting signals over large distances.

Derived from the Greek word ‘tele’ (τελε) meaning ‘far off’.

teleprocessing Processing data by using remote terminals connected to a

central computer.

template A document that is created for repeated use.

temporary storage Storage that is used to hold data for a relatively short time.

Temporary storage often uses a volatile storage medium.

terminal A device at which data may be input to or output from a

system. VDUs, together with their keyboards, are often known

as terminals.

terminal emulation The process by which the characteristics of one type of

terminal are translated into those appropriate for another type

of terminal before data is communicated to the host

computer.

termination condition A condition which is tested to determine whether or not a

statement within a repetition structure should be executed.

T

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Glossary of Terms

testing The process in which data identified during the design of a

program is provided as input to the program in order to test

all possible decisions, ensure that all statements are executed,

and that the solution provided is correct in all cases tested.

The set of test data must be selected to ensure that extreme

cases, boundary conditions and representative intermediate

cases are included.

See also boundary conditions.

text Data which consists of strings of printable charactersseparated by white space characters.

text editing In word processing, the changing, inserting or deleting oftext.

text editor Software used to create, change, print or display stored textfiles.

text file Similar to a word-processed file but with no formattingoptions or format control characters included.

time code A numbering system for identifying individual frames in avideo sequence or film.

time-sharing A method of operation in which a computer facility is sharedby several users for different purposes at (seemingly) the sametime. The high speed of the computer makes it appear thatthe users are handled simultaneously, even though they areactually handled sequentially in a series of short, interleavedactions.

time-slice A period of time allocated to an individual user in a time-sharing system.

title A label in a document or spreadsheet used to describe itsfunction.

titling The placement of a caption to accompany a picture or graphicelement.

token ring network A token is a string of bits signifying permission to transmit. Atoken ring network circulates the token continuously aroundthe ring, and a node will only transmit its data when itpossesses the token.

See also ring network.

top-down design An approach to program design that breaks a large,complicated problem into a series of smaller, easier-to-solveproblems. This leads to the creation of modules, thus reducingthe programming complexity.

See structured programming.

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translator (1) A program which converts statements written in one

programming language to the format of another programming

language. Includes compilers, interpreters and assemblers.

(2) A term sometimes used as a synonym for file conversion

filter.

tuple See relational database.

tweening The process of taking two images of an animation and

producing intermediate images so that the animation is

smoother.

type face A name given to the design of a set of characters, eg

Courier , Times, Helvetica.

type size A measure of the physical size of a type face, measured from

the top of the ascenders to the bottom of the descenders. The

unit of measurement is the point, where one point is equal to

0.351 mm (1⁄72 inch).

type style The name given to describe the general shape of the type face,

eg italic, normal, shadowshadow.

unguarded loop An alternative name for a repetition structure represented as a

REPEAT-UNTIL construct in which the termination

condition is tested after the loop body has been executed. The

body of such a loop must therefore be executed at least once

in a particular run of a program.

Compare with guarded loop.

upload The action of transferring a file from the user’s computer to

another (remote) computer.

Compare with download.

utility Also called utility program. A program that performs file

management functions, eg formatting a disk, making a

directory, duplicating files.

See also system utility.

utility software See utility.

U

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Glossary of Terms

V.42bis An ISO standard of a hardware data compression and

decompression technique.

validation A check carried out by the computer to ensure that only data

conforming to certain rules is accepted for input to the

program.

Compare with verification.

value One of the data types used in a spreadsheet. Values can be in

the form of number, currency, date, percentage etc.

variable The symbolic name of an addressed, stored entity in a

program that is referred to for later processing.

variable length record A record whose length may vary within certain limits

according to the requirements of the data. The end of the

record is indicated by a terminating symbol.

VDU Abbreviation for visual display unit. A synonym for monitor.

vector display A method of presenting data on a monitor in which vectors

are displayed as straight lines on a screen. The vectors are

defined only by their starting and finishing points.

verification A check, carried out by the user, of the entered data against

the source data.

Compare with validation.

virtual memory A memory management technique giving the illusion of the

computer possessing a larger primary memory than it does.

Secondary storage is used as an extension of primary storage by

the frequent swapping of data.

visual display unit See VDU.

voice input device A device (usually a microphone) in which speech is used to

input data or system commands directly into a system. Such

equipment involves the use of speech recognition processes, and

can replace or supplement other input devices.

volatile memory Memory that loses data when the power is switched off.

Normally used for temporary memory.

Compare with non-volatile memory.

V

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WAN Acronym for wide area network.

warping The distortion of an image by mathematical processes.

See also morphing.

‘what if’ prediction Testing a numerical hypothesis by using a spreadsheet. Values

are assigned to each variable and the spreadsheet is set up in

such a way that when the value of one variable is changed, the

effects of that change on all variables can be observed.

WHILE-DO A control structure in which the group of statements or

instruction within the body of the structure are executed while

the termination condition is true. The body of the structure

may never be executed.

Compare with REPEAT-UNTIL.

white space The space in a document produced by the deliberate insertion

(by the user) of white space characters, and the automatic

insertion of white space characters, leading and kerning by the

software. Care needs to be taken to ensure that the reader is

not distracted from the content of the text by inappropriate

white space.

white space character The name given to those ASCII characters, stored in memory,

which do not print out or become displayed on screen. They

include the characters for backspace, space, carriage return,

TAB, etc. Some word processing programs allow users to

examine white space characters stored within the text.

wide area network A network of computers designed to provide facilities for

inter-user communication beyond a single building or site.

Abbreviated to WAN.

Compare with local area network.

wildcard character A special character placed in the search string used in a pattern

matching program which will match any character in the string

being searched.

window That portion of the application visible on a screen.

wire frame An image of a three-dimensional object formed by drawing

only the edges of polygons representing the faces of solid

objects.

word The number of bits that are processed by the registers in the

CPU at one time.

W

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Glossary of Terms

word processing The creation, editing, manipulation, storage and retrieval of

text through the use of electronic equipment. In most word

processors simple graphics can be incorporated.

word processor An application that allows the user to enter characters and

create documents. The software allows text manipulation and

editing and storage for later retrieval and printing. Simple

graphics can usually be incorporated.

wordwrap In word processing, a text entry feature that automatically

advances any character string that will not fit at the end of a

line, to the beginning of the next line.

write protect notch/tab The notch/tab on floppy disks which is used by the disk drive

to prevent accidental erasure or overwriting of the disk

contents.

WYSIWYG Acronym for What You See Is What You Get. An

expression describing a program where the screen output will

show, complete with correct line breaks, pagination and any

special formatting, the hard copy that can be printed.

X modem A file transfer protocol in which the sending computer

transmits a packet and awaits an acknowledgment from the

receiving computer before either retransmitting the same

packet in response to a negative acknowledgment, or

transmitting the next packet in response to an

acknowledgment.

Compare with Z modem.

Z modem A file transfer protocol in which the sending computer

continuously transmits packets without waiting for an

acknowledgment from the receiving computer. The receiving

computer only transmits a negative acknowledgment when it

receives a corrupt packet which is then retransmitted.

Compare with X modem.

Z

X

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