Yuanfang cai room 104 university crossings 215 895 0298 yfcai@cs drexel edu
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Yuanfang Cai Room 104, University Crossings 215.895.0298 yfcai@cs.drexel.edu. CS 451 Software Engineering Winter 2009. Design within the Context of Software Engineering. Software Design. Between Requirement and Coding Including: Data Design Architectural Design Interface Design

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CS 451 Software Engineering Winter 2009

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Yuanfang cai room 104 university crossings 215 895 0298 yfcai@cs drexel edu

Yuanfang Cai

Room 104, University Crossings



CS 451Software EngineeringWinter 2009

Design within the context of software engineering

Design within the Context of Software Engineering

Software design

Software Design

  • Between Requirement and Coding

  • Including:

    • Data Design

    • Architectural Design

    • Interface Design

    • Component Design

    • Detailed Design

  • Need to be modeled, analyzed, and reviewed in industrial strength software.

Translating the analysis model into the design model

Translating the Analysis Model into the Design Model

Component Design

Interface Design

Architecture Design

Data/Class Design

Design process and desgin quality

Design Process and Desgin Quality

Design engineering

Design Engineering

  • Software design is an iterative process through which requirements are translated into a “blueprint” for constructing software

    • Abstraction

    • Refinement

Design engineering1

Design Engineering

  • A design must implement all of the explicit requirements contained in the analysis model, and it must accommodate all of the implicit requirements desired by the customer.

  • A design must be a readable, understandable guide for those who generate code and those who test and subsequently support the software.

  • The design should provide a complete picture of the software, addressing, the data, functional, and behavioral domains from an implementation perspective.

Design quality

Design Quality

  • FURPS – Functionality, Usability, Reliability, Performance, and Supportability.

  • Functionality – assessed by evaluating:

    • the feature set

    • capabilities of the program.

  • Usability - assessed by considering:

    • human factors,

    • overall aesthetics,

    • consistency,

    • end-user documentation.

Design quality functionality usability reliability performance and supportability

Design Quality - Functionality, Usability, Reliability, Performance, and Supportability

  • Reliability – is evaluated by measuring:

    • the frequency and severity of failure,

    • the accuracy, of output results,

    • the mean-time-to-failure,

    • the ability to recover from failure,

    • the predictability of the program.

  • Performance – is measured by:

    • processing speed,

    • response time,

    • resource consumption,

    • throughput,

    • efficiency

Design quality functionality usability reliability performance and supportability1

Design Quality - Functionality, Usability, Reliability, Performance, and Supportability

  • Supportability – combines:

    • the ability to extend the program (extensibility),

    • adaptability,

    • serviceability

    • testability,

    • compatibility,

    • configurability.

Design concepts

Design Concepts

Design concepts1

Design Concepts

  • Abstraction

    • Architecture

    • Patterns

    • Data

  • Modularity

    • Information Hiding

    • Functional Independence

    • Refinement

    • Refactoring

  • Design Classes

Design concepts abstraction

Design Concepts-Abstraction

  • “Abstraction is one of the fundamental ways that we as humans cope with complexity.” Grady Booch

  • “What kinds of things do we abstract?

    • data

    • objects

    • procedures

    • modules

    • just about anything

Design concepts architecture

Design Concepts-Architecture

  • Software architecture alludes to “the overall structure of the software and the ways in which that structure provides conceptual integrity for a system.

  • Architecture is:

    • the structure or organization of program components (modules),

    • the manner in which these components interact,

    • the structure of data that are used by the components.

Design concepts patterns

Design Concepts-Patterns

  • “A pattern is a named nugget of insight which conveys the essence of a proven solution to a recurring problem within a certain context amidst competing concerns.”

  • “Each pattern describes a problem which occurs over and over again in our environment, and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever doing it the same way twice.” Christopher Alexander

Design concepts modularity

Design Concepts -Modularity


    • “Modularity is the single attribute of software that allows a program to be intellectually manageable”

    • Software is divided into separately named and addressable components, sometimes called modules, that are integrated to satisfy problem requirements.

Design concepts information hiding

Design Concepts –Information Hiding

  • Modules should be specified and designed so that information (algorithms and data) contained within a module is inaccessible to other modules that have no need for such information.

  • This means that inadvertent errors introduced during modification are less likely to propagate to other locations within the software.

  • Changes to the internal representation of one module should have not have an effect on other modules.

Design concepts functional independence

Design Concepts-Functional Independence

  • Functional independence is achieved by developing modules with “single-minded” function and an “aversion” to excessive interaction with other modules.

  • We want to design software so that each module addresses a specific subfunction of requirements and has a simple interface when viewed from other parts of the program structure.

Design concepts functional independence1

Design Concepts-Functional Independence

  • Independence is assessed by using two qualitative criteria:

    • Cohesion – How related a module is to itself. It should perform a single task and require little interaction with the rest of the program.

    • Coupling is an indication of the interconnectoin among modules in a software structure.

Design concepts refinement

Design Concepts-Refinement

  • Stepwise refinement is when a program is developed by successively refining levels of procedural detail.

  • Refinement is actually the process of elaboration.

Design concepts refactoring

Design Concepts-Refactoring

  • Refactoring is a reorganizational technique that simplifies the design )of code) of a component without changing its function or behavior.

Design concepts design classes

Design Concepts-Design Classes

  • Refine analysis classes by providing design details

  • Create a new set of design classes that implement a software infrastructure to support the business solution

  • Five types:

    • User interface classes

    • Business domain classes

    • Process classes

    • Persistent classes

    • System classes

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