instructor: pavlos pavlikas1 how data is stored chapter 8

Instructor: Pavlos Pavlikas 1

How Data is StoredChapter 8


Data and InformationSurname

Baker

Class

C11

When data are put into structure, these become information


Database• Is a (large)

collection of data items and links between them, structured in a way that allows it to be accessed by a number of different applications programs.

Examples • Telephone Index• School’s Student• Hospital’s Patients• Books Information

Catalogue• GenBank


The parts of a database• Record: Is the basic unit of data stored in a

data file. It is the collection of items, which may be of different data types, all relating to the individual or object that the records describe (i.e. A Student)

• Field: Is a part of a record designed to hold a single data item of specified type (i.e. Student’s Name)


Key fields• Is the field within a record used to

identify the record. Most datafiles will have a primary key, which is unique and used to identify the record.


Fields

RecordsPrimary Key


Data type• Variable Type: In high-level languages

describes the kind of data held by a variable.

• Field Type: Describes the kind of data stored as a field within a datafile


Manual filing systemsProblems:• We cannot obtain information that is held on

several files• Because the data is not shared it is difficult to

update the information• An information can be accessed only by one

person at a time.• If a file is put back in the wrong place, finding

it again will be very difficult


Computerised databasesAdvantages• Access information from several files• Easy to update• Rapid access of information• Validation checks may be made on the

data on entry.


Computerised databasesDisadvantages• If the computer breaks down, you are

not able to access the details• Easy to copy files. Data must protected

by passwords• Training is needed to use the system


Database management system (DBMS)• DBMS is a software

that can find data in a database, add new data and change existing data.

Examples• Microsoft Access• SQL Server• Oracle• Paradox

Database


Relational database• Is a complex database structure to hold

a variety of different data. Where data items are related to each other, they are linked together by pointers stored in the database


Relational database• Table: is the name for each group of similar

data with rows for each member of the entity and columns for each attribute.

• Query: is a question asked of the data in the database.

• Report: is the presentation of the selected data. Reports are ready for printing.

instructor: pavlos pavlikas1 how data is stored chapter 8

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