软件工程导论期末复习.docx

软件工程导论期末复习.docx

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软件工程导论期末复习

软件工程概述部分

FAQsaboutsoftwareengineering

●WhatisSoftware?

Computerprogramsandassociateddocumentationsuchasrequirements,designmodelsandusermanuals（指南）.

Softwareproductsmaybedevelopedforaparticularcustomerormaybedevelopedforageneralmarket.

Genericproducts–通用软件产品

Bespoke（custom）products–制定软件产品

Characteristics1:

Softwareisdevelopedorengineered;Butitisnotmanufacturedintheclassicalsense.

（Thatmeanswecancopyyourproductwhenyoufinishthephaseofbuildingup.）

Characteristic2:

Softwaredoesn’t“wearout”

●WhatisSoftwareEngineering?

Softwareengineeringisanengineeringdiscipline（工程学科）thatisconcernedwithallaspectsofsoftwareproduction.

Softwareengineersshouldadoptasystematicandorganised（系统的，有组织的）approachtotheirworkanduseappropriatetoolsandtechniquesdependingontheproblemtobesolved,thedevelopmentconstraintsandtheresourcesavailable.

resources:

People（mostimportant）

Tools

Method

Process

●WhatisthedifferencebetweenSE（softwareengineering）andCS（computerscience）?

Computerscienceisconcernedwiththeoryandfundamentals;softwareengineeringisconcernedwiththepracticalitiesofdevelopinganddelivering（交付）usefulsoftware.

●Whatisthedifferencebetweensoftwareengineeringandsystemengineering?

systemengineeringisconcernedwithallaspectsofcomputer-basedsystemsdevelopment,includinghardwaresoftwareandprocessengineering（处理工程）.softwareengineeringisapartofthisprocess.

●Whatissoftwareprocess?

Asetofactivitieswhosegoalisthedevelopmentorevolutionofsoftware.

Genericactivitiesinallsoftwareprocessesare:

Specification（描述）-whatthesystemshoulddoanditsdevelopmentconstraints

Development（开发）-productionofthesoftwaresystem

Validation（有效性验证）-checkingthatthesoftwareiswhatthecustomerwants

Evolution（进化）-changingthesoftwareinresponsetochangingdemands.

●Whatissoftwareprocessmodel?

Asimplifiedrepresentation（表示形式）ofasoftwareprocess,presentedfromaspecificperspective.

softwareprocessmodel：

Workflowperspective-sequenceofactivities;

Data-flowperspective-informationflow;

Role/actionperspective-whodoeswhat.

软件过程部分

●Genericprocessmodels

ØWaterfall;（瀑布型）

——Separateanddistinctphasesofspecificationanddevelopment.（使用单独的过程阶段表现）

问题：

1.Inflexible（Onephasehastobecompletebeforemovingontothenextphase.）

2.Transferofrisks（风险转移）

适用：

mostlyusedforlargesystemsengineeringprojectswhereasystemisdevelopedatseveralsites

ØEvolutionarydevelopment;（进化式）

——Specification,developmentandvalidationareinterleaved（交替，先快速开发再不断修改）.

Exploratorydevelopment（探索式）：

toworkwithcustomers

Throw-awayprototyping（抛弃式）：

startwithpoorlyunderstoodrequirementstoclarifywhatisreallyneeded

问题：

1Lackofprocessvisibility（过程不可见）

2Systemsareoftenpoorlystructured

适用：

Forsmallormedium-sizeinteractivesystems

ØComponent-basedsoftwareengineering.（基于组件CBSE）

——Thesystemisassembledfromexistingcomponents.（集成已存在的可复用的组件）

软件复用reuse：

peopleworkingontheprojectknowofdesignsorcodewhichissimilartothatrequired.

●Processiteration软件迭代：

（Iterationcanbeappliedtoanyofthegenericprocessmodels.）

两个过程模型专门为过程反复设计的

Two（related）approaches：

ØIncrementaldelivery（增量式开发）;

——thedevelopmentanddeliveryisbrokendownintoincrements（增量）

Thehighestpriorityrequirementsareincludedinearlyincrements

Oncethedevelopmentofanincrementisfinished，correspondingsystemfunctionalityisavailable

ØSpiraldevelopment（螺旋式开发）.

——Eachloop（循环）inthespiralrepresentsaphaseintheprocess.

Risksareexplicitlyassessedandresolvedthroughouttheprocess.

●Fourfundamentalprocessactivities:

•Softwarespecification

•Softwaredesignandimplementation

•Softwarevalidation

•Softwareevolution

ØSoftwarespecification（描述）

ØSoftwaredesignandimplementation（设计和实现）

ØSoftwarevalidation（有效性验证）

Verificationandvalidation（V&V）V&Vmustbeappliedateachstageinthesoftwareprocess.

Hastwoprincipalobjectives：

Thediscoveryofdefectsinasystem;

Theassessmentofwhetherornotthesystemisusefulanduseableinanoperationalsituation

Verification:

"Arewebuildingtheproductright”.——Thesoftwareshouldconformtoitsspecification.

Validation:

"Arewebuildingtherightproduct”.——Thesoftwareshoulddowhattheuserreallyrequires.

ØSoftwareevolution（进化）

软件项目管理部分

●Softwareprojectmanagement

Concernedwithactivitiesinvolvedinensuringthatsoftwareisdeliveredontimeandonscheduleandinaccordancewiththerequirementsoftheorganisationsdevelopingandprocuringthesoftware.

●MilestonesVs.Deliverables

Milestonesaretheend-pointofaprocessactivity.（里程碑）

Deliverablesareprojectresultsdeliveredtocustomers.（可交付的文档）

软件过程被分解为一系列想关的基本活动，每个基本活动都有相应的输出结果。

里程碑不是要交给客户的东西。

而可交付的文档是要交付给客户的项目成果，要在项目的描述、设计等阶段结束时交付。

例如需求过程：

可交付的文档是：

需求描述

●CriticalPath

Longestofallpathsthroughtheproject

●WBS

软件需求部分

●SoftwareRequirementVs.SoftwareRequirementEngineering

Requirement：

Itmayrangefromahigh-levelabstractstatementofaserviceorofasystemconstrainttoadetailedmathematicalfunctionalspecification.Descriptionofsystemservicesandconstraintstoadetailmathematicalfunction.

Requirementsengineering：

Theprocessofestablishingtheservicesthatthecustomerrequiresfromasystemandtheconstraintsunderwhichitoperatesandisdeveloped.

Therequirementsthemselvesarethedescriptionsofthesystemservicesandconstraintsthataregeneratedduringtherequirementsengineeringprocess.

●软件需求类型

用户需求（userrequirement）

Statementsinnaturallanguageplusdiagramsoftheservicesthesystemprovidesanditsoperationalconstraints.Writtenforcustomers.

系统需求（systemrequirement）

Astructureddocumentsettingoutdetaileddescriptionsofthesystem’sfunctions,servicesandoperationalconstraints.Defineswhatshouldbeimplementedsomaybepartofacontractbetweenclientandcontractor.

系统需求包括：

功能性需求（Functionalrequirements）

Statementsofservicesthesystemshouldprovide,howthesystemshouldreacttoparticularinputsandhowthesystemshouldbehaveinparticularsituations.

Functionaluserrequirementsmaybehigh-levelstatementsofwhatthesystemshoulddo

Functionalsystemrequirementsshoulddescribethesystemservicesindetail.

非功能性需求（non-functionalrequirements）

constraintsontheservicesorfunctionsofferedbythesystemsuchastimingconstraints,constraintsonthedevelopmentprocess,standards,etc.

需求工程过程（从可行性分析到需求文档，这部分包括很多细致的内容，请参考教材和ppt）

Requirementsengineeringprocess：

Feasibilitystudies

•Afeasibilitystudydecideswhetherornottheproposedsystemisworthwhile.

•Ashortfocusedstudythatchecks

◦Ifthesystemcontributestoorganisationalobjectives;

◦Ifthesystemcanbeengineeredusingcurrenttechnologyandwithinbudget;

◦Ifthesystemcanbeintegratedwithothersystemsthatareused.

Elicitationandanalysis

•Sometimescalledrequirementselicitationorrequirementsdiscovery.

•Involvestechnicalstaffworkingwithcustomerstofindoutabouttheapplicationdomain,theservicesthatthesystemshouldprovideandthesystem’soperationalconstraints.

•Mayinvolveend-users,managers,engineersinvolvedinmaintenance,domainexperts,tradeunions,etc.Thesearecalledstakeholders.

Requirementsvalidation

•Concernedwithdemonstratingthattherequirementsdefinethesystemthatthecustomerreallywants.

•Requirementserrorcostsarehighsovalidationisveryimportant

◦Fixingarequirementserrorafterdeliverymaycostupto100timesthecostoffixinganimplementationerror.

Requirementsmanagement

•Requirementsmanagementistheprocessofmanagingchangingrequirementsduringtherequirementsengineeringprocessandsystemdevelopment.

•Requirementsareinevitablyincompleteandinconsistent

◦Newrequirementsemergeduringtheprocessasbusinessneedschangeandabetterunderstandingofthesystemisdeveloped;

◦Differentviewpointshavedifferentrequirementsandtheseareoftencontradictory.

ReviewQuestionsforyou!

●WhatisSoftwareRequirement?

●Whodoesit?

●Whyisitimportant?

●Whatarethesteps?

●Whatistheworkproducts（artifacts）?

●HowdoIensurethatI’vedoneitright?

●WhataretheCASEforourrequirementanalysis?

软件体系架构设计部分

●SoftwareArchitectureVs.ArchitectureStyle

Thedesignprocessforidentifyingthesub-systemsmakingupasystemandtheframeworkforsub-systemcontrolandcommunicationisarchitecturaldesign.

Theoutputofthisdesignprocessisadescriptionofthesoftwarearchitecture.

软件设计部分

SoftwareDesign:

Designiswhatvirtuallyeveryengineerwantstodo.Itistheplacewherecreativelyrules-customersrequirements,businessneeds,andtechnicalconsiderationsallcometogetherintheformulationofaproductorsystem.

DesignPrinciples:

•Abstraction抽象

抽象是控制复杂性的基本策略。

“抽象”要求人们将注意力集中在某一层次上考虑问题，而忽略那些低层次的细节。

•Modularity模块性

•InformationHiding信息隐藏

•FunctionalIndependence功能独立

Coupling耦合——单元模块之间

Onemoduleisreferencedbyothermodules

Datatransportedfromonemoduletotheothers

耦合度是对软件结构中模块间关联程度的一种度量。

耦合的强弱取决于模块间接口的复杂性、进入或调用模块的位置以及通过界面传送数据的多少等。

与内聚度正好相反，在设计软件时应追求尽可能松散耦合的系统。

因为对这类系统中任一模块的设计、测试和维护相对独立。

由于模块间联系较少，错误在模块间传播的可能性也随之变小。

模块间的耦合程度直接影响系统的可理解性、可测试性、可靠性和可维护性。

耦合度也可以分为七级

Lowercoupling

No-directCoupling

无联系耦合：

如果两模块中任一个都不依赖于对方能独立工作，则称这两模块为（nodirectcoupling），这类耦合度最低。

DataCoupling

StampCoupling:

特征耦合：

介于数据耦合和控制耦合之间的一种耦合

印记耦合：

将数据结构作为参数进行传递

ControlCoupling:

控制耦合：

传递标志

如果两模块间通过参数交换信息，此时若传递的信息中含有控制信息，则耦合度上升为控制耦合。

控制耦合通常会增加系统的复杂性，有时适当分解模块可消除控制耦合。

Externalcoupling

外部耦合：

一些模块都与一个外部环境相关，则这