2

Approaches to Requierements Engineering

Reference: Systems Analysis and Design in a Changing World, 3rd Edition, chapter 2 and

chapter 6

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Systems Analysis and Design in a Changing World, 3rd Edition 2

Overview

Systems development life cycle (SDLC)

Provides overall framework for managing system development process

Two main approaches to SDLC

Traditional approach: structured systems development and information engineering

Object-oriented approach: object technologies requires different approach to analysis, design, and programming

All projects use some variation of SDLC

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Traditional and Object-Oriented Views of Activities

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Requirements Models for the Traditional and OO Approaches

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Structured Analysis

Define what system needs to do (processing requirements)

Define data system needs to store and use (data requirements)

Define inputs and outputs

Define how functions work together to accomplish tasks

Data flow diagrams and entity relationship diagrams show results of structured analysis

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Context Diagrams

DFD that summarizes all processing activity

Highest level (most abstract) view of system

Shows system boundaries

System scope is represented by a single process, external agents, and all data flows into and out of the system

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Context Diagram for RMO Order-Entry Subsystem

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Data Flow Diagrams

Graphical system model that shows all main requirements for an IS in one diagram

Inputs / outputs

Processes

Data storage

Easy to read and understand with minimal training

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DFD Fragment from the RMO Case

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Data Flow Diagram (DFD) created using Structured Analysis Technique

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Data Flow Diagram Symbols

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Entity-Relationship Diagram (ERD) created using the Structured Analysis

technique

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Structured Analysis Leads to Structured Design and Structured Programming

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Object-Oriented Approach Views information system as collection of

interacting objects that work together to accomplish tasks

Objects - things in computer system that can respond to messages

No processes, programs, data entities, or files are defined – just objects

Object-oriented analysis (OOA)

Defines types of objects that do work of system

Shows how objects interact with users to complete tasks

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Object-Oriented Approach to Systems

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Object-Oriented Approach (continued)

Object-oriented design (OOD)

Defines object types needed to communicate with people and devices in system

Shows how objects interact to complete tasks

Refines each type of object for implementation with specific language of environment

Object-oriented programming (OOP)

Writing statements in programming language to define what each type of object does

Benefits of OOA include naturalness and reuse

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Class Diagram Created During OO Analysis

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Summary (continued)

System development methodologies are based on traditional approach or object-oriented approach

System development methodology provides guidelines to complete every activity in the SDLC

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Summary

Data flow diagrams (DFDs) used in combination with event table and entity-relationship diagram (ERD) to model system requirements IN TRADITIONAL APPROACH TO REQUIREMENS

DFDs model system as set of processes, data flows, external agents, and data stores

DFDs easy to read - graphically represent key features of system using small set of symbols

Many types of DFDs: context diagrams, DFD fragments, subsystem DFDs, event-partitioned DFDs, and process decomposition DFDs