structured analysis. graphic, easy to understand partitioned process, clear picture of progression...

Structured Analysis

Structured AnalysisGraphic, easy to understand Partitioned process, clear picture of progression from general to specific

Logical rather than physical Precise, concise and highly readable

Tools of structured analysis

Data Flow Diagram

Data Dictionary

Structured English

Decision Tree

Data Flow DiagramA DFD is graphical representation which shows

the ‘FLOW OF DATA’. It is used for the visualization of data processing

for structured design.It shows interaction between the system and

outside entity.It is also called bubble chart. It is starting point in the system design that

decomposes to lowest level.It consist of series of bubbles joined by lines.

Bubbles represents transformations.

DFDIt has four symbols 1. External Entity 2. Data Flow

3. Data Store

4. Process

Explation of symbols of DFDThe EXTERNAL ENTITY symbol represents

source of data to the system. External entities determine system boundaries. They are beyond the area of influence of the developer.

The DATA FLOW represents movement of data. Data flow represents ‘DATA IN MOTION’. Data flows are always named. Names should be some identifying noun. For example: order, payment etc.

Explanation of symbols of DFDThe DATA STORE symbol represents data that is

not moving. Data stores are repository of for data. It is an ‘inventory’ of data. Data stores are named with an appropriate name. For example: Customers, Orders, Products.

The PROCESS symbol represents an activity that transforms or manipulates the data. Processes are actions performed on incoming data flows to produce outgoing data flows. All processes must have some inputs and outputs. Major functions of processes are making decisions.In

put

Process

Output

Advantages of DFDUnderstanding interestedness of

systems and sub systems.Communicating current system

knowledge to the user.Part of system documentation files.Logic underlining.Easy to follow errors.

Disadvantages of DFDPhysical consideration neglected.

Large number of alteration.Ambiguous.

Data DictionaryDD is structured repository of data. It keeps

the details of data flows, process and data stores. It documents the list of contents of all data flows.

It has three classes:- Data Element

Datastructure

DataFlow

Data Store

Data DictionaryClasses of DD are:-

1. Data elements: smallest unit of data further cannot be decomposed.

2. Data structure: group of data elements.

3. Data Flows and Data Stores: Data flows are data structures in motion. Data stores are data structures in store.

Advantages of Data DictionaryValuable referenceImproves communicationCompare data descriptionCross referenceBuild database

Disadvantage is that it do not provide details

Structured EnglishIt uses logical constructs to carry

out instructions for data (actions)Decisions are made through the use

of IF, THEN, ELSE and SO statements.

It is highly correlated to the decision tree.

ExampleStructured English version of the sales

promotion policy:- IF customer is a preferred customer , and IF customer orders more than $1000,

THEN apply a 5% discount, and IF customer uses

our charge card, THEN apply an additional 5% discount ELSE award $25 bonus coupon ELSE award $5 bonus coupon.

Decision TreesThey sketch out logical structure based on

some criteria. It is a graphical representations of the conditions, actions and rules found in a decision tree.

DIAGRAMATIC REPRESENTATION

PREFERREDCUSTOMER?

ORDER MORE THAN $1000?

USED OUR CHARGE CARD ?

$25 BONUS COUPON

NO

$5 BONUS COUPON

5% DISCOUNT AND AN

ADDITIONAL 5% DISCOUNT

5% DISCOUN

T

Advantages of decision treeEasy to understandBusiness rues are mapped easilyReal problems solvedNo prior assumptionsProcess both numerical and

categorical data

Disadvantages of decision treeOutput attribute must be categorical

Limited to one output attribute only

Decision tree algorithms are unstable

complex

Decision TableIt is single representation of the

relationship between conditions and actions.

A condition is usually given a value of ‘Y’ for ‘YES’, it is true, ‘N’ for ‘NO’ and a dash for ‘DO NOT CARE’.

Decision tree fails to tell us what conditions to test, a decision table can carry out the conditions to test.

Features of decision tableDefines problem and actionsRelationship between condition and

actionTwo parts :- (1) stub (2) entryStub has two parts:- (a) condition

stub (b) action stubEntry has two parts (a) condition

entry (b) action entry

Decision table diagram Condition Stub Condition

Entry 1 2 3 4

5 6 7 8Preferred customer Y Y Y Y N

N N NOrdered more than $1000 Y Y N N Y

Y N NUsed our charge card Y N Y N Y

N Y N

5% discount x xAdditional 5% discount x$ 25 bonus coupon x$5 bonus coupon x x

x x x Action stub Action entry

Advantages of decision tableConcise description of logically complex

situationEasier to draw and change than flow

chartsEasier to follow a particular path down

one column than through several flow charts pages

Limitation large decision tables can become difficult

to modify