Lecture 6 Design Evaluation and Basic Patterns

Applying UML and Patterns: An Introduction to Object-Oriented Analysis and Design and Iterative Development (3rd Edition)

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Copyright W. Howden 1 Lecture 6: Design Evaluation and Intro to OO Design Patterns
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Copyright W. Howden 2 Principles • Domain Simulation • Information Hiding • Cohesion and Coupling • Design Patterns
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Copyright W. Howden 3 Domain Simulation • Structure of system reflects structure of application domain • Concepts and relationships derived from domain analysis • Concept classes -> system classes • Concept associations -> static class relationships
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Copyright W. Howden 4 Domain Simulation Benefits • Domain changes less likely than functionality changes • Functionality changes less likely to upset basic design structure
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Copyright W. Howden 5 Information Hiding • Design decisions “hidden in modules” – Changes to implementation details can be localized • Access to information via public methods/routines rather than direct access • An original motivation for OO approach
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Copyright W. Howden 6 Information Hiding Examples • DS Subsystems – GUI, Domain Logic, DataBase – DL and DB are components with subsystem proxy interfaces • All requests for DL and DB services are made to those proxies • Proxies hide how these responsibilities are designed and implemented
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Copyright W. Howden 7 Cohesion and Coupling • Design expressed in terms of inter-related components • Cohesion – Things in components belong together – Cohesion should be strong • Coupling – Connections between components – Coupling should be weak
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Copyright W. Howden 8 Extreme Cases • Single component – Bad cohesion – Good coupling • Components contain a “single thing” – Good cohesion – Bad coupling • Design is a balance between cohesion and coupling
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Copyright W. Howden 9 General Levels of Cohesion • Coincidental • Logical • Temporal • Procedural • Data Flow • Communicational • Functional
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Copyright W. Howden 10 Coincidental • Accidental, no functional rationale • Division of code into modules determined by size consideration • Isolation of commonly used but not functionally related pieces of code
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Copyright W. Howden 11 Logical • Group things together that are the same kind of thing • E.g. Module containing all the error handling routines • E.g. Initialization module that opens files, initializes variables, etc.
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Copyright W. Howden 12 Temporal • Group things together than can be done at the same time • E.g. Initialization code • E.g. Termination/clean up
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Copyright W. Howden
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This note was uploaded on 02/11/2008 for the course CSE 111 taught by Professor Howden during the Fall '07 term at UCSD.

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Lecture 6 Design Evaluation and Basic Patterns - Lecture 6:...

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