2
Approaches to Requierements
Engineering
Reference: Systems Analysis and Design in a
Changing World, 3rd Edition, chapter 2 and
chapter 6
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
Systems Analysis and Design in a Changing World, 3rd Edition
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Traditional and Object-Oriented Views of
Activities
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3
Requirements Models for the Traditional
and OO Approaches
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2
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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2
Context Diagrams
 DFD
that summarizes all processing activity
 Highest
 Shows
level (most abstract) view of system
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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2
DFD Fragment from the RMO Case
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Data Flow Diagram (DFD) created using
Structured Analysis Technique
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2
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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2
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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2
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
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