CS 451 Software Engineering Winter 2009Design within the Context of Software EngineeringSoftware DesignTranslating the Analysis Model into the Design ModelDesign Process and Desgin QualityDesign EngineeringDesign EngineeringDesign QualityDesign Quality - Functionality, Usability, Reliability, Performance, and Supportability Design Quality - Functionality, Usability, Reliability, Performance, and Supportability Design ConceptsDesign ConceptsDesign Concepts-AbstractionDesign Concepts-ArchitectureDesign Concepts-PatternsDesign Concepts -ModularityDesign Concepts –Information HidingDesign Concepts-Functional IndependenceDesign Concepts-Functional IndependenceDesign Concepts-RefinementDesign Concepts-RefactoringDesign Concepts-Design ClassesSlide Number 23Drexel University CS 451 Software Engineering Winter 2009 1 Yuanfang Cai Room 104, University Crossings 215.895.0298 [email protected] University Design within the Context of Software Engineering 2Drexel University 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. 3Drexel University Translating the Analysis Model into the Design Model 4 Data/Class Design Architecture Design Interface Design Component DesignDrexel University Design Process and Desgin Quality 5Drexel University Design Engineering  Software design is an iterative process through which requirements are translated into a “blueprint” for constructing software  Abstraction  Refinement 6Drexel University 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. 7Drexel University 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. 8Drexel University 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 9Drexel University Design Quality - Functionality, Usability, Reliability, Performance, and Supportability  Supportability – combines:  the ability to extend the program (extensibility),  adaptability,  serviceability  testability,  compatibility,  configurability. 10Drexel University Design Concepts 11Drexel University Design Concepts  Abstraction  Architecture  Patterns  Data  Modularity  Information Hiding  Functional Independence  Refinement  Refactoring  Design Classes 12Drexel University 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 13Drexel University 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. 14Drexel University 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 15Drexel University Design Concepts -Modularity  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. 16Drexel University 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. 17Drexel University 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. 18Drexel University 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. 19Drexel University Design Concepts-Refinement  Stepwise refinement is when a program is developed by successively refining levels of