Introduction to Design Structured AnalysisDesign

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Introduction to Design/Structured Analysis/Design

• CS2335
• Fall 2003

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Agenda

• Design Principles
• Common Design Techniques
• SA/SD

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Software Development Life Cycles
Project Planning
Requirements
Analysis
Design
Implementation
Testing
OM
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What is Design?
The process of applying various techniques and
principles for the purpose of defining a device,
a process or a system in sufficient detail to
permit its physical realization.
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Levels of Design (Formality)

• None (Code and Fix)
• Back of the envelope
• Structured
• Object-Oriented
• Formal Methods

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Why Design?
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Design Stages

• Analysis
• Software Architecture
• Preliminary Design
• Detail Design

Moving from as-is to to-be
Moving from language of the user to language of
the machine
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Design Principles

• Good organization and control
• Modular
• Separable representation of data
• Independent modules
• Simple interfaces
• Repeatable method
• Build vs Buy

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Key Design Ideas

• Abstraction
• Refinement (Stepwise, Elaboration)
• Modularity (235)
• Information Hiding (339)
• Cohesion (single task) (232)
• Coupling (interconnection) (229)

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Quality Design Issues

• Performance
• Usability
• Usefulness
• Reliability
• Extensibility
• Modifiability
• Reusability
• Safety
• Security

CONSTRAINTS
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Design Strategies

• Top Down (Decomposition)
• Bottom Up (Aggregation/Composition)
• Hybrid

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Lab 4 Top Down Functional Decomposition
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Lab 4 Bottom-Up Functional Composition
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Design Techniques

• SA/SD
• Object Oriented
• Object Modeling Technique (OMT)
• Rational Unified Process (UML)
• Shellor-Mellor
• Objectory
• Ad Hoc

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Now.
Structured Analysis (SA) Structured Design
(SD)
Data Dictionaries
Context Diagrams
Data Flow Diagrams
Module Hierarchy
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Structured Analysis

• Context Diagram
• Data Flow Diagram (DFD)
• Data Dictionary (DD)
• Procedure Specification (PSPEC)

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Context Diagrams
What is in system? (System Boundary) What do we
have to interface with? (External Actors)
User
Display Info
Payroll System
0. System
Keypress Info
Employee Salary Info
Budget System
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Lab 4 Context Diagram
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Data Flow Diagrams
What are processes? What is information being
processed? How does information flow between
processes?
1. Process
Information Flow
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Example DFD
Configuration Information
User
2. Update Config
Keypress Info
1. Input Handler
Display Info
Selection Info
4. Display Results
3. Process Salary Data
Expenditure Data
Employee Salary Info
Payroll System
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Lab 4 Data Flow Diagram
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Data Dictionary
What is the definition and makeup of the data in
the data flows?
Name Employee Number Alias SSN Where/How
Used Process Salary, indexes employees Descriptio
n string length 9
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Lab 4 Data Dictionary
Name Alias Where/How Used Description
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Procedure Specification
Pseudo-code spec of decomposed process Use for
comments in actual code.
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Structured Design

• Refine DFD as necessary
• Determine type of information flow
• Establish flow boundaries
• Map DFD onto program structure
• Factor control hierarchy
• Refine program structure

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Flow Determination
Employee Salary Info
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First Level Factoring
Main Controller
Input Handler
Output Handler
Data Transform Engine
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Second Level Factoring
Main Controller
Input Handler
User Display Manager
Data Transform Engine
User Input Handler
Payroll Interface
Salary Processor
Configuration Manager
Then refine structure based on principles
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Lab 4 Structured Design
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Unified Modeling Language

• Three Amigos Booch, Rumbaugh (OMT), Jacobson
  (OOSE)
• OMG Standard
• CASE Tool Support (Rational Rose)
• For this class Version 1.5
• OCL Formal Specifications

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Model and View Diagrams
Implementation View
Class Diagram Object Diagram
Component Diagrams
User View Use Case Diagrams
Structural View
Deployment Diagram
Sequence Diagram Collaboration Diagram Statechart
Diagram Activity Diagram
Behavioral View
Environment View
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Why so many diagrams?
Different stakeholders
Different concerns
Why not just one blueprint for a skyscraper?
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Next Time
UML Class Diagrams Sequence Diagrams