chapter15 finalizing design specifications

Copyright 2002 Prentice-Hall, Inc.

Modern Systems Analysisand Design

Third Edition

Jeffrey A. Hoffer Joey F. George

Joseph S. Valacich

Chapter 15Finalizing Design

Specifications

15.1

Learning ObjectivesDiscuss the need for system design specificationsDefine quality requirements and write quality

requirements statementsRead and understand a structure chartDistinguish between evolutionary and throwaway

prototypingExplain the role of CASE tools in capturing design

specificationsDemonstrate how design specifications can be

declared for Web-based applications

15.2

Introduction

Need for systems to be developed more quickly todayThe lines between analysis and design and design and implementation are blurring Traditional approaches allowed for a break

between design and implementation Other approaches, such as CASE and prototyping,

have caused overlap between the two phases

15.3

The Process of Finalizing Design Specifications

Less costly to correct and detect errors during the design phaseTwo sets of guidelines Writing quality specification statements The quality of the specifications themselves

Quality requirement statements Correct Feasible Necessary Prioritized Unambiguous Verifiable

15.4


Quality requirements Completely described Do not conflict with other requirements Easily changed without adversely affecting

other requirements Traceable back to origin

15.5


Deliverables and Outcome Set of physical design specifications

Contains detailed specifications for each part of the system

15.6

Representing Design Specifications

Traditional Methods Pre-CASE Documents written natural language and

augmented with graphical models Specification documents

Figure 15-2 shows an example Several methods for streamlining

Computer-based requirements tools Prototyping Visual development environments

15.7


Structure Charts Shows how an information system is

organized in hierarchical models Shows how parts of a system are related to

one another Shows breakdown of a system into

programs and internal structures of programs written in third and fourth generation languages

15.8


Structure Charts Module

A self-contained component of a system, defined by a function

One single coordinating module at the root of structure chart Single point of entry and exit Communicate with each other by passing parameters

Data couple A diagrammatic representation of the data exchanged

between two modules in a structure chart Flag

A diagrammatic representation of a message passed between two modules

15.9


Structure Charts Module

Special Symbols Diamond

Only one subordinate will be called Curved Line

Subordinates are called repeatedly until terminating condition is met

Predefined modules Hat

Subordinate module is important logically but code is contained in superior module

15.10


Structure Charts Pseudocode

Method used for representing the instructions inside a module

Language similar to computer programming code

Two functions Helps analyst think in a structured way about the

task a module is designed to perform Acts as a communication tool between analyst and

programmer

15.11


Prototyping Construction of the model of a system Allows developers and users to

Test aspects of the overall design Check for functionality and usability

Iterative process Two types

Evolutionary Prototyping Throwaway Prototyping

15.12


Prototyping Evolutionary Prototyping

Begin by modeling parts of the target system If successful, evolve rest of the system from the

prototype Prototype becomes actual production system Often, difficult parts of the system are

prototyped first Exception handling must be added to prototype

15.13


Prototyping Throwaway Prototyping

Prototype is not preserved Developed quickly to demonstrate unclear

aspect of system design Fast, easy to use development environment

aids this approach

15.14


Prototyping Oracle Designer: An Example

Transforming and Generating the Database Entity-Relationship Diagramming Tool Database Design Transformer Tool Server Model Diagram End Result

Generation of Data Definition Language (DDL) scripts

Create database by running scripts

15.15


Prototyping Oracle Designer: An Example

Transforming and Generating Software Modules

Data Flow Diagram Functional Hierarchy Diagram Application Design Transformer

Transforms diagrams into software modules which can be used to generate forms or reports

Generate form or report in Design Editor

15.16

Radical Methods: eXtreme Programming

Short cyclesIncremental planning approachAutomated testsUtilizes two-person programming teamPlanning, analysis, design and construction are fused together into one phaseRequirements and specifications are uniquely captured

15.17


Planning game Players

Business Development

Story cards Description of procedure or system feature

15.18


Planning game Three phases

Exploration Business creates a story card Development responds with time estimate

Commitment Business sorts story cards into three stacks Development sorts story cards according to risk Business selects cards to include in next release of product

Steering Business monitors development activity

15.19


Iteration Planning Game Played by programmers Task Cards

Several task cards generated for each story card Three phases

Exploration Story cards converted to task cards

Commitment Programmers accept responsibility for tasks

Steering Programmers write code, test it and integrate it

Game takes place during time between intervals of planning game steering phase meetings

15.20

Radical Methods: RAD

Four life-cycle phases Planning Design Construction Cutover

Iteration between design and construction

15.21

Electronic Commerce Application

Microsoft FrontPage used to build throwaway prototypeTemplate based HTML

15.22

Summary

Types of Design Specifications Written document augmented by various

diagrams Structure chart Computer-based requirements

management tool Prototypes

Throwaway versus Evolutionary

15.23

Summary

Radical Methods eXtreme Programming RAD

Electronic Commerce Application Throwaway prototyping

15.24