A&D - DT, DD, DFD

Tools for Structured Design

Organized By: Vinay Arora

Assistant Professor

CSED, Thapar University

www.slideshare.net/aroravinay

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Disclaimer

This is NOT A COPYRIGHT MATERIAL

Content has been taken mainly from the following books:

System Analysis and Design Methods By Jeffrey L Whitten & Lonnie D Bentley ,

Analysis & Design of Information Systems By James A. Senn,

System Analysis & Design By Elias M. Awad,

Modern System Analysis & Design By Jeffrey A. Hoffer, Joey F.George & Joseph

S. Valacich

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Tools for Structured Analysis

For the Business System under Investigation DECISION & PROCEDURES are Important to System Analyst.

Various TOOLS are present for Studying Operational Procedures and Decision Making Steps.

TOOL – A Device, Object or Operation used to accomplish a Specific Task.

Three TOOLS for Documenting Procedures:

Decision Tree, Decision Table and Structured English

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Structured English

� STRUCTURED ENGLISH is the use of the English Language with the

SYNTAX of Structured Programming.

� STRUCTURED ENGLISH aims at getting the benefits of both the

Programming Logic and Natural Language.

� Program Logic helps to attain precision while natural language helps in

getting the convenience of spoken Languages.

� Method to Overcome Problem of AMBIGUOUS Language.

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Guidelines when writing Structured

English

� Statements should be Clear and Unambiguous

� Use One Line per Logical Element

� All LOGIC should be expressed in Operational, Conditional and

Repetition Blocks

� Logical Blocks should be indented to show Relationship

� Keywords should be Capitalized

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Structured English (contd.)

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Common Keywords

� START, BEGIN, END, STOP, DO, WHILE, DO WHILE, FOR,

� UNTIL, DO UNTIL, REPEAT, END WHILE, END UNTIL, END

� REPEAT, IF, IF THEN, ELSE, IF ELSE, END IF, THEN, ELSE

� THEN, ELSE IF, CASE, EQUAL, TRUE, FALSE, AND, OR, XOR

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Developing Structured Statements

Structured English uses THREE Basic Types of Statements to describe a

PROCESS:

� SEQUENCE STRUCTURES

� DECISION STRUCTURE

� ITERATION STRUCTURES

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Sequence Structures

� A Single Step or Action Included in a Process.

� None of the Steps contains a Decision or any Conditions that determine whether the steps are taken.

� Operation Statements written as ENGLISH PHRASES executed from the top down.

Example:

1). Pick Out a Desirable Book

2). Take the Book to the Checkout Counter

3). Pay for the Book

4). Obtain a Receipt

5). Leave the Store

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Decision Structure

� Another way of Showing Decision Analysis.

� Decision Structures occur When TWO or MORE Actions can be taken,

depending on the value for a Specific Condition.

� After Decision Making Stated Actions or Sets of Actions for that

Condition will be taken.

� Once Condition is made, ACTIONS are Unconditional.

� Keywords Like IF/THEN/OTHERWISE are used.

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Example

IF a desirable book is found, THEN

Take the book to the checkout counter.

Pay for the book.

Be sure to obtain a receipt.

Leave the store.

OTHERWISE

Do not take the books to the checkout counter.

Leave the Store.

END IF

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Iteration Structure

� Iteration Instructions permit Analyst to Describe the cases where:

Certain Activities are repeated WHILE a certain Condition Exists

OR

UNTIL a Condition Occurs

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Example

DO WHILE Still examining more books.

Read the title of the Book.

IF the title sounds interesting

THEN pick up the book and thumb through it.

Look at the Price.

IF you decide you want the book

Put it in the DESIRABLE BOOK stack.

ELSE Put it back on the shelf.

END IF

ELSE Continue

END DO

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IF Desirable books are found THEN

Take the books to the checkout counter.

Pay for the books.

Be sure to obtain a receipt.

Leave the store.

ELSE

Do not take books to the checkout counter

Leave the store

END IF

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Tree Structure

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Decision Tree

� Conditions – Possible States of an ENTITY.

� Action – What to do when certain condition/s occur…

� Actions are the Alternatives.

� Tools used in Understanding & Matching combinations are -

- Decision Trees

- Decision Tables

- Structured English

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Decision Tree

� Decision Tree – Diagram that presents CONDITIONS and ACTIONS

sequentially.

� Shows which CONDITIONS to consider First which Second and so on.

� Method of showing the relationship of condition & its permissible

actions.

� Diagram resembles branch of a TREE.

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Decision Tree – Basic Layout

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Decision Tree Sample

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Decision Tree Example

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Decision Tree (cont.)

� Formal Identification of Actual Decision.

� Force Analyst to Consider the Sequence of Decisions.

� Drawback of Decision Tree – A Large number of branches with many

paths through them will cloud rather than aid analysis.

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Decision Tree for Invoice Processing

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Example Decision Tree – Students Data

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Example Decision Tree – Students Data – Take

student as root node

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Example Decision Tree – Students Data – Take

income as 2nd node

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Example Decision Tree – Students Data (contd.)

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Decision Table

� Decision Table – Matrix of Rows & Columns, rather than a TREE.

� Decision Rules are present in Decision Table.

� Decision Tables are a Precise yet Compact WAY TO MODEL complicated

logic.

� Decision Tables, like If-Then-Else and Switch-Case Statements,

ASSOCIATE CONDITIONS WITH ACTIONS to perform.

� Decision Rule – Procedure to follow when certain Conditions Exits.

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Decision Table

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Decision Table – Example Health Services

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Decision Tree - Example

Longer than 10 Days Within 10 Days

Over $10000

$5000 to $10000

Take 2% Discount from

Invoice TotalTake 3% Discount from

Invoice Total

Pay Full Invoice Amount

Below $5000

Pay Full Invoice Amount

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Relation of Condition & Action

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Decision Table – Example Payment

Discount

� There are various Formats of Decision Tables. Format doesn’t Change

the Usefulness of Decision Table.

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Building Decision Table - Steps

1- Determine most relevant factors to consider in making a DECISION.

2- Determine the most feasible steps or activities under varying conditions.

3- Study the Combinations of Conditions that are Possible.

4- Fill in the Table with DECISION Rules.

5- Mark Action entries with ‘X’ to signal action(s).

6- Examine Table for Redundant Rules.

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Decision Table –Payment Discount Example

Using Yes/No Format

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Checking Decision Table

� Eliminating Redundancy

� Removing Contradictions

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Common Discrepancies

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Decision Table – Discrepancies Removed

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Types of Table Entries

� Limited Entry Form

� Extended Entry Form

� Mixed Entry Form

� ELSE Form

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Decision Table – Limited Entry

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Decision Table – Extended Entry

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Decision Table – Mixed Entry

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Decision Table – Else Form

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Data Dictionary

� DATA DICTIONARY – Can be defined as a CATALOG or a

REPOSITORY of the Elements in a SYSTEM.

� To Manage details in a Large System.

� To Document the features of a System.

� To Communicate a Common Meaning for all System Elements.

� Record in DD – Data Element, Data Structure.

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Data Dictionary

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Data Dictionary

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Describing Data Elements

� Data Names

� Data Description

� Aliases

� Length

� Data Value

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Relation b/w components

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Describing Data Structures

� Sequence Relationship

� Selection Relationship

� Iteration Relationship

� Optional Relationship

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Sequence Relationship

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Selection Relationship

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Iteration Relationship

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Optional Relationship

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Notation for Structural Rel. in Data

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Data Structure for Student Data

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Data Description & Notation

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Data Flow Name

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Data Structure

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Data Element

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Process

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Structured Analysis Components

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DFD – A Tool for data flow analysis

� DFD - A Structured, Diagrammatic technique for showing the functions performed by a System & the data flowing Into, out of & within it.

Following Data-Oriented Questions about a Target System:

� What processing is done?

� What data is Needed?

� The Context Diagram (Level 0 DFD) is the Highest Level in a Data Flow Diagram and contains only One Process, representing the ENTIRE SYSTEM.

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DFD Style - Yourdon

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DFD Style - Yourdon

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DFD Style - Gane and Sarson

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DFD Style - Gane and Sarson

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Expanding Modules – while locating Thapar

University using Google maps – Step 1

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DFD – Expanding Modules

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DFD Principles

� A System can be decomposed into Subsystems and Subsystems can be

decomposed into Lower Level Subsystems and so on.

� Each Subsystem represents a Process or Activity in which data is

processed.

� At the Lowest Level, Processes can no longer be decomposed.

� Just as a System must have Input and Output, so a Process must have

Input and Output.

� Data Enters the System from the Environment, Data Flows between

Processes within the System and Data is produced as Output from the

System.

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Rules for constructing DFD

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DFD Example – A Restaurant

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DFD Example - A Restaurant

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DFD Level 0 (A Restaurant)

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DFD Level 1 (A Restaurant)

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Division of Main Program in Modules

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Example – DFD Construction

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Example – DFD Construction (contd.)

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Presentation Graph

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Physical DFD

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Division in Modules

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Context Diagram (DFD Level -0)

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DFD Level -1

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Expanding – Invoice Approval (DFD Level -2)

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Expanding - Revise Balance Due (DFD Level -2)

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Expanding - Write Vendor Checks (DFD Level -2)

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Example – Context Diagram

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DFD Level 0

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Sequence of Logical & Physical View

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Physical & Logical DFD

� WHAT the System does - Current Physical DFD

� HOW it does it - Current Logical DFD

� WHAT it should do - Required Logical DFD

� HOW it should do it - Required Physical DFD

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1st Level DFD – Account Payable Processing

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2nd Level DFD – Invoice Approval

Process

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2nd Level DFD - Maintaining Vendor

Balance (A/C Posting)

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2nd Level DFD – Vendor Payment

Processing (Cheque Writing)

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1st & 2nd Level DFD

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3rd LEVEL

DFD

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Reference List

1. System Analysis and Design Methods By Jeffrey L Whitten & Lonnie D Bentley

2. Analysis & Design of Information Systems By James A. Senn

3. System Analysis & Design By Elias M. Awad

4. Modern System Analysis & Design By Jeffrey A. Hoffer, Joey F.George & Joseph S. Valacich

5. http://yourdon.com/strucanalysis/wiki/index.php?title=Chapter_9

6. http://www.ehow.com/about_5095247_definition-data-flow-diagrams.html

etc…….

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Thnx…

Education

A&D - DT, DD, DFD