system analysis and design by parool jain

8/3/2019 System Analysis and Design by Parool Jain

1/62

Structured analysis


2/62

2

Problem Analysis and Fact Collection

Objectives determine the organizational structure and its purpose, the

problem areas, the environment around the organisation and

identify the boundaries of the problem

establish a detailed specification of the problem

validate the gathered information

Techniques for Fact Collection documentation review, interviewing, questioning, observation,

measuring

Preliminary Fact Documentation Matrices, Flowcharts, etc.


3/62

Traditional approach

Traditional approach of organize and convert the

data through system flowcharts.

Flowchart only represent a physical rather than

logical systems. it makes difficult to distinguish

between what happens and how it happens

pros & cons of traditional approach

1. No accurate comm. with user. They have nolanguage in common.

2. No tools avail to structure and control the

details(business and technical)


4/62

Definition of Structured analysis

Structured analysis is a set of techniques and

graphical tools that allow the analyst to

develop a new kind of system specification

that are easily understandable to the user.

Analysts work primarily with their wits, pencil

and paper. [Kendall 1996]


5/62

Goals of Structured Analysis

Improve Quality and reduce the risk of system failure

Establish concrete requirements specifications and

complete requirements documentation.

Focus on Reliability, Flexibility, and Maintainability ofsystem

Use graphics to communicate better to user.


6/62


7/62

Tools of structured analysis

DFD (data flow diagram)

Also known as bubble chart Clarify system requirement & identify major

transformations.-that will become programs in

system design

DFD describe what data flow (logical)rather than how

they are processed so it does not depend on

hardware software, data structure or file organization


8/62

8

DFD

SYMBOLS

A square defines a source or destination of system data:

An arrow identifies data flow-data in motion: it is a pipeline

through which info. Flow

A circle or a bubble represents process that transform

incoming data flow (s) in to outgoing data flow(s).

An open rectangle is a data store-data at rest or temporaryrepository of data.


9/62

Why do we use DFDs?

It is a way of taking the physical view and converting itinto a logical view.

The physical view - all documents involved. The logical view - the data they contain. Their main purpose is to communicate with the user, the

analysts understanding of the scope of the requiredsystem

Constructing DFD:

1. Process should be named and numbered for easyreference

2. The direction of flow from top to bottom and from left toright

3. When a process is exploded into lower level details,they

are numbered ex:process 5 is exploded in tosubprocesses 5.1 and 5.24. The names of data stores ,sources,destinations,are

written in capital letters5. Process and data flow names have the first letter of each

word capital


10/62

Central Concepts

Process (data transformation) activities that transform data

related by dataflows to other processes, data

store, and external entities.

Data flow indicate passage of data from output of one

entitie to input of another

represent a data group or data element

Data store a place where data is held for later use

Data stores are passive: no transformations

are performed on the data

External entity An activity outside the target system

Acts as source or destination for dataflows

that cross the system boundary

External entities cannot interact directly with

data stores

Data group A cluster of data represented as a single

dataflow

Consists of lower level data groups, or

individual elements

Data element a basic unit of data


11/62

Sources(external entities)

Any class of people, anorganization, or anothersystem which existsoutside the system youare studying.

Form the boundaries ofthe system.

The system and external

entities exchange data inthe form of data flows.

Must be named, titlespreferred to names of

individuals - use a noun

source/


12/62

Data Flows data in motion marks movement of data through the

system - a pipeline to carry data connects the processes, external

entities and data stores Unidirectional originate OR end at a process (or both) name as specifically as possible -

reflect the composition of the data - anoun

do not show control flow! Control flowis easy to identify- a signal with onlyone byte - (on/off).

HINT: if you can't name it: either it'scontrol flow, doesn't exist or you needto get more information!


13/62

Processes transform incoming data

flows into outgoing dataflows

represent with a bubble orrounded square

name with a strongVERB/OBJECTcombination; examples:

create_exception_reportvalidate_input_characters

calculate_discount

process


14/62

Data Stores data at rest represents holding areas for

collection of data, processesadd or retrieve data fromthese stores

name using a noun (do notuse file)

only processes are connectedto data stores

show net flow of databetween data store and

process. For instance, whenaccess a DBMS, show onlythe result flow, not therequest


15/62

Data Flow Diagram Donts

1. BLACK HOLES

2. MIRACLES

4. Leave things UNLABELED

(corollary: labels should have meaning)

5. Data stores that are SOURCES6. Data flows that are UNASSOCIATED with

a PROCESS

7. Expect your diagram to be perfect thefirst time!


16/62


processstuff

1. Black Hole

processstuff

2. Its a Miracle


17/62


4. Leave Things Unlabeled

Corollary: Labels Should

Have Meaning


18/62


data store 5. Miracle datasource

data store 5. Black hole datasource


19/62


6. Data Flows Unassociated With a Process

entity toentitydata store

to entity -or reverse

data storeto datastore


20/62

Diagramming A System

multiple DFDs are required to represent a system

DFDs are created at increasing levels of detail

Advantages of DFD

Represents data flows

Provides good system documentation.

Process bubbles can be hierarchically decomposed into sub-DFDs; the inputs

and outputs must match at all levels of decomposition, so the design has

validation.

Easily understand after a brief orientation.

Disadvantages

Weak in its display of input and output details.

Major problem is large number of iterations that are require forcomplete solution.


21/62

Level n: subprocesses

3.1

request

res.

3.2.

log 3.3.

track

booking

system

Request id.Request id.

timestamps booking

confirmation

bookingrequest

preferences

Level n: subprocesses

3.1

request

res.

3.2.

log 3.3.

track

booking

system

Request id.Request id.

timestamps booking

confirmation

booking

requestpreferences

Level 2: subprocesses

3.1

request

reser-

vations

3.2.

confirm

booking

3.3.

collate

confirm-

ations

booking

systemReq id.

Req id.

seat

data

booking

confirmation

booking

request

seating prefs

Hierarchies of DFDs

ticket

system

booking

system

customer

ticketsbooking

confirmation

booking

request

customer

query

Level 0: Context Diagram

check

schedule

issue

tickets

Proposed

itinerary

booked

itinerary

booking request

1.

determine

form of

travel

2.

check

schedule

3.

reserve

seats4.

issue tickets

Timetables

Fare tables

customer

booking

systemcustomer

travel

request

customer

query

schedule

proposed

itinerary

proposeditinerary

booked

itinerary

fares

tickets

booking

confirmation

booking

request

Level 1: Whole System


22/62

Data dictionary

It is a structured repository ofdata about

data. Although we give descriptive names to

the data flows, process and data stores in a

DFD, it does not give the details. Hence tokeep the details of the contents of data flows,

process and data stores we also require a Data

Dictionary.It clearly documents the list ofcontents of all data flows, processes and data

stores.


23/62

The three classes to be defined in data dictionaryare:

Data Elements: - this is the smallest unit of data.

Further decomposition is not possible. Data Structure: - this is a group of Data Elements

which together form as a unit in a data structure.For ex BOOK DETAIL is a data structure

consisting ofdata elementsauthor name , title ,publisher name ,quantity etc.

Data flows and Data stores: - data flows are datastructures in motion.

Data Stores are data structures at rest or in store .(Data structures in a data store - a data store is alocation where data structures are temporarilylocated.)


24/62

Logical data description hierarchy

Smallest unit of data

Group of data element

Groups of data

structures


25/62

Describing data elements The description of data elements should include the

Name , description & an alias(synonym)

Ex- AUTHOR NAME:

-first

-middle

-last-alias

2. description should be summary of data element

We may include whether or not the data element has:.

3. A different name or alias for ex:purchase order mayexist as P.O or PUR.ORDER.


26/62

Describing data elements..(cont..)4. Usage characterstics ,such as range of value , value is a

code that represent a meaning

Here 2 types of data elements:-a)Those that take a value within a range ex:-a check

amount between rs.1 and 10,000rs is called continuousvalue.

b)Those tat have a specific value:-for ex-department in afirm may be coded 100(accounting),110(personnel)etc.

In data dictionary it is describe as follows: 100 meansAccountingdepartment

101 means accounts receivable section

In either type values are coded that represent a meaning.

5.Control information such as the source , date oforigin,users,or access authorization.


27/62

Describing data structure

Data structure are group of data element ex-

BOOK DETAIL

We describe data structure by specifying the

name of each data structure and the elements

it represents. Some elements are mandatory where else

some are optional.


28/62

illustrate it with example BOOK DETAILS

mandatory optional

Data structure BOOK-DETAILS

Data elements AUTHOR NAME X

TITLE OF BOOK X

EDITION X

ISBN(international

standard book number)

X

PUBLISHER NAME X

QUANTITY ORDERED X


29/62

Complete DFD ,showing

accounts receivable routineof book ordering system


30/62

Describing data flows and data stores The contents of a data flow may be described by the

name of the data structures that passes along it(label

name of data flow is the name of content it carry withit).

EX-

BOOK DETAILS expresses the content of the data flow that leads toprocess 4

Additionally we may specify source of data flow , the destination and thevolume.


31/62

Using BOOK ORDER example data flow may be

describe as follows:-

Data flow comments

BOOK-DETAILS From new comb hall book store(SOURCE)

AUTHOR-NAME

TITLE OF BOOK

EDITION Recent edition required

QUANTITY Minimum 40 copies


32/62

Data store

Data store may be describe by the data

structures found in it and the data flows thatfeed it or are extracted from it.

For example: the data store BOOKSTORE-ORDER

is described by the following contents:Comments

ORDER

ORDER-NUMBER Data flow/data structure feeding data store

CUSTOMER-DETAILS Content of data store

BOOK-DETAIL Data flow/data structure extracted from

data store

Describing processes


33/62

Describing processes Describing process is a logical description.

We want to specify input and output for the

process and summarize the logic of the system.

in figure process EDIT-ORDER can be described

as shown:-

1.Name of process Edit order is O.K.

2.Short description Verify and decide whether customer

credit is OK for authorising shipment

3.input logic Output

ORDER Look up customer

payment record

If new bookstore

,clear credit rating

Credit OK,no

balance remainder

Customer payment

file


34/62

Decision Tree What is it?

A structure that can be used to divide up a large

collection of records into successively smaller sets of

records by applying a sequence of simple decision rules

A decision tree model consists of a set of rules fordividing a large heterogeneous population into smaller,

more homogeneous groups with respect to a particular

target variable

Decision tree has many branches as there are logical

alternatives


35/62

Example - Grades

Percent >= 90%?

Yes Grade = A

No 89% >= Percent >= 80%?

Yes Grade = B

No 79% >= Percent >= 70%?

Yes Grade = C

No Etc...


36/62

Decision Tree Template Drawn top-to-bottom or left-

to-right

Top (or left-most) node =

Root Node Descendent node(s) = Child

Node(s)

Bottom (or right-most)

node(s) = Leaf Node(s)

Unique path from root to

each leaf = Rule

Root

Child Child Leaf

LeafChild

Leaf


37/62

Decision Tree Advantages

1. Easy to understand,construct and update

2. Map nicely to a set of business rules

3. Applied to real problems

4. Make no prior assumptions about the data

5. Able to process both numerical and

categorical data


38/62

Decision Tree Disadvantages

1. Output attribute must be categorical

2. Limited to one output attribute

3. Trees created from numeric datasets can be

complex

4. Lack of information in its format to tell us

what other combination of condition to test.

Decision tree -Example


39/62

Decision tree -Example

discountSize oforder

Type ofcustomer

Discountpolicy

Book store

6 or more 25%

Less that 6 nil

Libraries or

individual

50 or more

20-49

10%

6-19

5%

15%

Less than 6nil


40/62

Structured English Structured English borrows heavily from

structured programming . It uses logical construction to carryout instruction

for action.

Decisions are made through IF THEN ELSE and SOstatement.

In this tool ,the logic of the processes of thesystem is expressed by using the capitalized

keywords Sentence should also be clear ,concise, and

precise in wording and meaning


41/62

Example of structured english(compute discount)

COMPUTE DISCOUNT

Add up the number of copies per book title

IF order is from book store

and IF order is for 6 copies or more per book title

THEN :Discount is 25%.

ELSE (order is for fewer than 6 copies per book title)SO:no discount is allowed.

Else (order is from libraries or individual customers)

So-IF order is for 50 copies or more per book titlediscount is 15%....

ELSE IF

ELSE IF.


42/62

Decision tables Decision table is a table of contingencies for

defining a problem and the action to be taken

It is a single representation of the relationshipbetween condition and actions.

Decision table consist of two parts: stub andentry.

The stub part is divided into an upper quadrantcalled the condition stub and the lower quadrantcalled action stub

The entry part is also divided into an upperquadrant called the condition entry and the lowerquadrant called action entry


43/62


44/62

System performance and its phase

A system required performance is defined by

describing its output in a user acceptable

format and at a higher level of detail.

This involve three steps:-

1.Statement of constraints

2.Identification of specific system objectives

3.Description of outputs.

1 Statements of constraints


45/62

1.Statements of constraints Constraints are the factors that limits the solution of the problem

Constraints are factors that lie outside - but have a direct impact on - thesystem design effort. Constraints may be:

Laws and regulations - for example, State, Federal (central or national ), orindependent regulatory agencies may require specific design approachesfor new systems or mandate specific changes to existing systems.

Technological - for example, new equipment must be compatible withexisting equipment;

Financial - for example, proposed development and implementation costsmust remain within a specified budget.

Operational - for example, space, staffing levels, skill mix, and capabilityand competence factors may limit system options.

However, system constraints should not be used to artificially restrict ordirect the system. The objective is to plan the best system for the problemto be solved, not to fabricate and impose constraints that limit the systemalternatives.

As with objectives, system constraints are critical to ensuing phases of thefeasibility study. They can affect system requirements and theacceptability of alternatives.



46/62


Analyst identify the systems specific performance objectives.

Specific objective are derived from initial investigation and system benefitsare then translated into measurable objective.

In example of safe deposit billing system ,the candidate systems benefitsare :-

a. Improved collection schedule:- collection is improved be billing 30 daysin advance of the box renewal date and one more notice is sent within 2weeks

b. Cost reduction:-online billing require less labor and work hour.

c. Physical space reduction:-replace one computer in place of 4 desks.d. improved customer service:-place box rental info online. Provide forms

online reduce waiting time.

These information is used as a basis for preparing specific objective forcandidate system:-

To establish a billing system with six-five days cycles per month

To mail customer a reminder two week after the initial statement for boxrenewal

To examine the availability of boxes by size, rental fees and location

D i ti f t t


47/62

Description of output

Final step in system performance definition is

Describing the output required by the user An actual format and content of report

Media used , frequency , size and number of

copies required are prepared at this point. Specifying exactly what the output will look

like leads to an estimate of computer storagerequirement that form the basis for file

design. The analyst is now evaluate feasibility of

candidate system to produce these outputs


48/62

Kendall & Kendall Copyright 2002 by Prentice Hall, Inc. 3-48

Feasibility

A feasibility study assesses the operational,

technical, and economic merits of the

proposed project

There are three types of feasibility:

Technical feasibility

Economic feasibility

Operational feasibility


49/62


Technical Feasibility

Technical feasibility assesses whether the

current technical resources are sufficient for

the new system

If they are not available, can they be upgraded

to provide the level of technology necessary

for the new system

T h i l F ibili


50/62

Technical Feasibility:

Can We Build It?

Users and analysts familiarity with the

business application area

Familiarity with technology

Have we used it before? How new is it?

Project size

Number of people, time, and features

Compatibility with existing systems


51/62

2 - 51

Can we build it? Feasibility

Technical

Do we have the capability to develop the system?

Does the necessary tech exist? Can it be acquired?

Does the proposed equipment have the right capacity for the

data?

Does the propose have the right: response time, interface,

Can the system be expanded?

Are the accuracy, reliability, ease of use, ease of access, security

ok?


52/62


Economic Feasibility

Economic feasibility determines whether the

time and money are available to develop the

system

Includes the purchase of

New equipment

Hardware

Software

E i F ibilit


53/62

Economic Feasibility

ShouldWe Build It?

Identify costs and benefits

Assign values to costs and benefits

Determine cash flow

Assess financial viability

Net present value

Return on investment

Break even point


54/62

2 - 54

Should we build it?

Economic

Is there an economic payoff?

include cost to conduct full systems integration

cost of hardware/software/ other

benefits in terms of reduced costs

opportunity costs


55/62


Operational Feasibility

Operational feasibility determines if the

human resources are available to operate the

system once it has been installed

Users that do not want a new system may

prevent it from becoming operationally

feasible

Feasibility study


56/62

Feasibility study

It is the measure and the study of how beneficial the

development of the system would be to theorganization. This is known as feasibility study. Themeasurement of feasibility is known as feasibility study.There are number of aspects which are taken into

consideration while the feasibility studies. Firstly theproject team is formed then with the help offlowcharts and other forms of documentations thecharacteristics of the system are identified. The systemis evaluated and measured against the expectedperformance. A suitable candidate is selected for thejob and a final report is made and presented to themanagement for further evaluations.

Steps in feasibility analysis


57/62

Steps in feasibility analysisThere are number of steps in the feasibility study, some of them are:-

1) Forming a team for the specific project and appointing a suitable leader.

2) Preparing layouts and flowcharts of the system :-charts bring up

importance of input , output, and data flow

3) Enumerate(list, detail ,catalog) the candidate systems:- consideration of

hardware that can handle the total system requirements. There are large

number of computers with different processing sizes, main memory

capabilities and software support . The project team may contact vendorsfor information on processing capabilities of the system available.

4 ) Identify and describe the characteristics of the candidate systems:-from

the candidate system considered(number of candidate systems)the team

begins to evaluate to reduce them into manageable number determine

what each candidate system can or cannot do.

St i f ibilit l i ( t )


58/62

Steps in feasibility analysis(cont.)

5) Determining the performance and cost effectiveness of eachcandidate system:-each candidate system performance is evaluatedagainst the system performance requirements set prior to

feasibility study. there has to be as close a match as practicable.Costs are easily determined when benefits of system are tangible and

measurable.

Evaluation criteria IBM PC HP 100 APPLE III

Performance

Response time Very good Very good Very good

User friendly excellent Very good Very good

Costs

System

development

good Very good Good

User training excellent good good

6) Reviewing the performance of the system and performing the cost data:-in somecases performance and cost data for each candidate system show which system is


59/62

cases ,performance and cost data for each candidate system show which system isbest choice. This outcome terminate the feasibility study. but some situation arenot clear cut so the next step is to weight the importance of each criterion byapplying the rating figure. Then the candidate with high score is selected.

The procedure for weighting candidate system is simple

1. Assign the weighting factor to each evaluating criteria based on the criteriaeffect on the success of the system

2. Assign a quantitative rating to each criterions qualitative rating for ex(good,fair)may be assign values (1,2,3,4,5)

3. Multiply the weight assign to each criterion by the relative rating to determinethe score

4. Sum the score column of each candidate.

Evaluation

criterion

Weighting

factor

IBM PC HP 100 APPLE III

Rating score Rating score Rating score

performance

Response time 2 4 8 3 6 4 8

User friendly 3 5 15 4 12 4 12

Costs

System

development

5 3 15 2 10 4 20

User friendly 3 5 15 3 6 5 25


60/62

7) Selecting the best candidate for the system

8)preparing the final report for the management

Feasibility report


61/62

Feasibility reportIt is a formal document for management brief enough and sufficiently

non technical to be understandable. No standard format forpreparing feasibility report. The report contain the following

section:- 1. Abstract : shows general findings .

2. Summary

3. Contents list (specifies various parts of report)

4. Glossary (dictionary,vocabulory,wordbook)

5. Introduction or overview (purpose and scope)

6. Discussion (the main body providing the evidence /outline themethod used in present system also provide objective ,generalprocedure, output, report ,cost and benefits use appendixes ifnecessary)


62/62

Feasibility report(cont..)

7. economic justification details: point by point costcomparisons and preliminary cost estimates fordevelopment and operation of candidate system.

8. Recommendations (flowing naturally from theconclusions) and Conclusions (flowing naturally from thediscussion)

9. References (if necessary)

10. Appendixes (document all data and memos and datacompiled during the investigation. They are placed at theend for reference.)

system analysis and design by parool jain

Documents