软件需求分析复习要点 (2).doc

Software Engineering n A discipline for the systematic production and maintenance of software developed by a team, which is n fault-free, n delivered on time,n within budget, andn satisfies the users needs n GOAL: to produce a good quality software that is useful for peopleProperties of High quality softwareDefect freeMeet users needsIn time Within budgetn Communication:n Project initiation, Requirements gatheringn Planningn Estimating, Scheduling, Trackingn Modelingn Analysis & Specificationn Designn Constructionn Code, testingn Deploymentn Delivery, support, maintenancen Requirementsn Definition需求明确地规定解决用户问题的方法n Their ImportanceThe set of requirements constitute a contract between the client and the software developerIt should be written such that all stakeholders can understand what the system will do.It allows developer to map problem domain concepts to solution domain concepts n ClassificationFunctional requirements（具体的系统功能要求）Nonfunctional requirements(可靠性，可用性，性能等等)Design constrains（限制设计者和实现者的规定）n Requirements Managementn Definition A systematic approach to eliciting ,documenting, organizing and tracking changing requirementsn ProcessElicitation: work with the customer on gathering requirementsAnalysis: process this information to understand it, classify in various categories, and relate the customer needs to possible software requirementsSpecification: Structure the customer input and derived requirements as written documents and diagramsValidation: youll ask your customer to confirm that what youve written is accurate and complete and to correct errorsn Users Needs , Features and Requirementsn DifferencesA reflection of the business, personal, or operational problem that must be addressed in order to justify the use of a new systemA service the system provides to fulfill one or more stakeholder needsSkill1n Definition of Problem Analysisthe process of understanding real-world problems and user needs and proposing建议提议 solutions to meet those needsn What is Root Causes Analysis?An identified reason for the presence of a defect or problem.The most basic reason, which if eliminated, would prevent recurrence.The source or origin of an event.n How to address the problem:n Step 1: Gain agreement on the problem definitionn Step 2: Understand the root causesn Step 3: Identify the stakeholders and the usersn Step 4: Define the solution system boundary.n Step 5: Identify constraints to be imposed on the solutionSpecific Problem Analysis Techniques n Business modelingn Applicable to IS/IT applicationsn Systems Engineeringn Applicable to software-intensive systems in the embedded-system domainSkill2n requirements elicitationInvolves technical staff working with customers to find out about the application domain, the services that the system should provide and the systems operational constraintsn Techniques for eliciting requirementsn Interviews and questionnairesn Requirements workshop (Definition)n Brainstorming sessions and idea reductionn Storyboards n Scenario-based Requirements Elicitation Actor, Use Cases ,ScenarioUse casea technique for capturing找准 the functional requirements of the system 定义：A use case describes the typical interactions between the users of a system and the system itself that yield a result of value to the users帮助理解：A use case contains a set of scenariosScenario describes sequences of actions a system performs that yield an observable result of value to a particular actorSkill3n Use-Case ModelSystem Context - summarizes the high-level behavior of a systemn What the system does (as a black-box)n What lies outside of the systemn How it gets used Use-Case Model: requirements in contextn Step-By-Step Building of the Use-Case ModelStep 1: Identify and describe the ActorsStep 2: Identify the use Cases and write a Brief DescriptionStep 3: Identify the Actor and use-Case RelationshipsStep 4: Outline the Individual Use CasesStep 5: Refine the Use Casesn Hierarchy of Use Cases levels1 Summary to define a broad scope of the system2user goal Satisfies a particular and immediate goal of value to the primary actor.3 subfunctionsatisfies a partial goal of a user-goal use case or of another subfunctionn Relationships between use casesn (for common sub-behavior)n (a single event interrupts the main success scenario multiple times; or there is an important alternative to emphasize)n (to capture abstraction)n Main Requirements Artifactsn Vision Document defines high-level business requirements, user needs and features.n Use-case model.n Supplementary Specificationsn Domain Modelis a representation of real-world conceptual classes参考：Domain model may be considered a visual可见的 dictionary of the noteworthy 值得注意的abstractions, domain vocabulary 词汇and information content of the domain.n Domain Model and Class diagramn Differencesn Relationsn UML diagrams for the Analysis Modeln Organizing RequirementsSkill4n Project ScopeProject ScopeThe work that needs to be accomplished to deliver a product, service, or result with the specified features and functions.1Product ScopeThe features and functions that characterize a product, service, or result.Certainly a project team can do at most R x T. What is project scope?n Requirements baseline (definition)需求基线，通俗点说就是把这些需求都划一根“线”，说明这些需求已经确定下来，添加新的需求和修改原有的需求都必须通过需求变更流程来操作。目的就是为了防止需求的滥变给程序架构造成重大影响n Steps to Defining a Requirements BaselineHave feature list at hand.For each feature:1. Establish priority 2. Assess effort required to develop feature.3. Risk involved in developing feature.Skill5n Technical Methods for Specifying Requirementsn pseudocode 伪代码n Decision Tables/Decision Tree n Extended Finite State Machinesn Activity DiagramsUsed to naturally represent flows of events in scenarios A state transition diagram where all states are action statesVery easy to write and understandEnables a representation of branching, repetition and process forkingSimpleParallel activitiesConditionalSignalReviewn Entity-Relationship DiagramSkill6Tracing RequirementsManaging ChangeCh