软件体系结构

软 件 体 系 结 构体 系 结 构 评 审Architectural Reviews孙 志 岗 Architectural Reviewsn Architectural reviews are a key step in architecture-based development. They include a method (such as SAAM or ATAM), but the full practice includes more than that.体系结构评审是开发过程中的一个重要环节。有专门的评审方法(SAAM、ATAM)，但在实践中并不仅仅是这些n We will discuss cost/benefits of architectural reviews different architectural review techniques preconditions for an architectural review architectural review activities outputs from an architectural review Costs of Architectural Reviewsn There are three different types of costs of holding regular architectural reviews.direct staff costs直接员工开销organizational overhead组织管理开销indirect staff costs间接员工开销 Examples of Direct Staff Costsn AT each has a different cost and provides different information.有很多种评审技术。每种需要不同的开销，提供不同的信息n These techniques fall into one of two categories. questioning techniques: applied to evaluate any aspect of an architecture for any given reason提问技术：用来评价体系结构的任何方面 measuring techniques: applied to answer questions about a specific quality度量技术：回答关于某项质量的问题 Questioning Techniquesn Scenario-based techniques describes a specific interaction between stakeholders and a system描述角色与系统交互的过程 example: SAAM, ATAM (partially)n Questionnaire-based techniques（基于问卷的技术） Some questions apply to all architectures (especially those in a single domain).有些问题被用于所有的体系结构，尤其是在单一领域内 Some questions ask about details of a specific architecture.有些问题询问一个特定结构的细节 Some ask about the development process.n “Is there a single architect?”n “How do you ensure conformance?”“你们怎样保证一致性？” Questioning Techniquesn Questionnaires are reused; they reflect more maturity or experience within a domain.问卷可以重用；它们体现了在一个领域内的成熟度和经验是否丰富n Scenarios must be developed anew for each system.场景必须为每个系统重新开发 Measuring Techniquesn Metrics: quantitative interpretations of observable measures量度：可测质量的定量说明 complexity metrics identify areas where modifications may be difficult复杂度的测量指明在哪个区域修改会很困难 performance metrics suggest areas where bottlenecks may occur性能的测量提示瓶颈会在哪里发生n Reviews tend to focus on results of metrics度量的结果 assumptions underlying the interpretation of the metrics (e.g., assumed event distribution)对度量的解释中的潜在假定 Measuring Techniquesn Simulations, prototypes, experiments: domain specific models of an architecture or performance model仿真、原型、实验：建立体系模型或者性能模型are expensive to createoften exist as part of development anywayn May answer issues raised by questioning technique 可以回答提问技术提出的问题“What evidence do you have that performance is adequate?”“你凭什么说可以达到这个性能？” Properties of Review Techniques评审技术通用性细节等级阶段被评审对象提问技术问卷通用粗糙早期设计和过程场景特定系统中等中期设计度量技术度量通用或者特定领域好中期设计仿真原型 实验特定领域不定早期设计 Review Processn An architectural review has three major elements.preconditions: the set of necessary assets and conditions that must be in place before a review can be performed successfully前提：评审成功进行之前，必要的资源和条件必须到位activities of the review itself活动：评审本身 outputs: the report of review results输出：评审结果报告 Review Preconditionsn Understand the context of the review理解评审的上下文n Assemble the right people集合正确的人n Set organizational expectations and support期望和支持n Prepare for review为评审做准备n Obtain representation of the architecture获得体系结构文档 Preconditions: Contextn Planned review part of normal development activity正常开发活动的一部分 non-adversarial（非敌对性的） scheduled well in advance（事先安排好日程） built into projects schedule and budget包含在项目日程和预算之内n Unplanned usually occurs when project is in trouble通常在项目出现问题时采用 often devolves into finger-pointing导致互相责备 can be painful for project already struggling对于已经苦苦挣扎了很久的项目而言，有些痛苦 Preconditions: Contextn Timing of the reviewearly “architecture discovery review”n is done after requirements are set, but before the architecture is firm需求分析之后，体系结构还没有确定之前进行n is used to understand implications of requirements on architecture用来理解需求在体系结构方面的隐含内容 n checks for requirements feasibility（检查需求的可行性）n prioritizes architectural goals（为质量目标排序）full architectural reviewn is done when architectural documentation is available体系结构文档可用时进行n is used to evaluate qualities of proposed architecture评价被评体系结构的质量 Preconditions: Peoplen Representatives of project（项目代表） architect designers of major modules stakeholders representativesn Review team members (ideally, a separate unit)评审团成员(理想情况下是一个独立组织) at least one domain expert included至少有一个领域专家 someone to handle logistics (e.g., meeting rooms, supplies)后勤人员(会议室、茶水、食品) librarian to organize documentation文档管理员“apprentice reviewer” for growth成长中的评审员学徒 Preconditions: Review Teamn The review team must be assembled so thatmembers are perceived as impartial, objective, and respected成员要公正、客观和被尊重members devote their full-time effort to the review成员全心加入评审members are fluent in architecture and architectural issues成员要训练有素而且口才好 it is located close to artifacts being examined有足够的权限检查被评审材料 Preconditions: Review Teamn The team must have access toapplicable domain knowledge (perhaps via consultants to the team)适当的领域知识design documents设计文档review criteria评审标准support staff支持人员 Preconditions: OrganizationalExpectationsn A contract between the review team and the sponsor of the review must be established.Who will be told what upon completion?结束后，哪些内容可以被告诉哪些人What will (not) be the review criteria?什么是(不是)评审标准？What/who will be made available to team?哪些人和物是评审团可以使用的？What follow-up is expected?希望评审的结果如何？ How long will the review take?要评审多久？ Preconditions: OrganizationalExpectationsn Organizational culture and support must be considered. Are reviews part of the standard project life cycle?评审是项目的基本生命周期的一部分吗？ Is serving on a review team considered good for ones career?为评审团服务是份好差事吗？ Will the organization allow its superior designers time off from their projects to serve on review teams?企业允许它的高级设计师把他的项目放在一边来参加评审吗？ Is there a standing review organization (even though members may rotate on and off)?有常设的评审组织吗(即便成员常进进出出)？ Preconditions: Read-Ahead Materialn For project being reviewed questionnaires scenarios (These are created as part of the review, but time should be allowed for project members to digest the information.)n For review team description of architecture rationale for architecturen Ideally, material will address the review questions. (Passing this test because the questions were known in advance is not cheating, but good engineering!)理想情况，材料要能说明评审时的问题 Preconditions: Ranked Qualityand Behavioral Requirementsn Plan to examine three to five quality and behavioral requirements.计划检查3到5个质量和行为需求n A particular representation medium (language) for the architecture is not necessary. As long as the information can be extracted (using project members as necessary), the form of the representation is not important.一个专门的体系结构表述媒体(语言)目前并不是必须的。由项目成员来讲解信息，表述的形式并不重要 Review Activitiesn Evaluate“Run” the scenarios and ask the questions, or answer the items in the checklist.按场景执行，并询问相关问题；或者回答问卷里的问题Perform the experiments.（演示实验）Execute the prototypes or simulations.运行原型或仿真程序n Recordcritical issues highlighted in the review评审中发现的严重问题 comments of project members on these issues项目成员对这些问题的说明 Review Activitiesn Rank the issuesproject-threatening（生死攸关）majorminorn Each issue raised should be addressed in terms ofchanging the architecturerelaxing the requirements Review Activitiesn Warning signsarchitecture forced to match organization组织模式影响体系结构top-level components number over 25顶层组件数超过25个one requirement drives entire design一项需求决定整个设计architecture depends on alternatives in the operating system体系受操作系统选择的影响 Review Activitiesn Warning signschoice of software components is dictated by hardware personnel由硬件人员选择软件组件redundancy not needed for reliability面对可靠性时，不考虑冗余手段design is exception driven零散的小的事件影响设计no identifiable architect没有确定的架构师 Output from Reviewn Set of ranked issues supporting data contained in formal report feedback to projectn Enhanced system documentation增强的系统文档n Set of scenarios for future use将来会用到的场景集n Identification of potentially reusable components认定潜在的可重用组件 n Estimation of costs and benefits估算成本和收益 SAAM: Software Architecture Analysis Method 一种简单的基于场景的评审技术 Qualities Are Too Vague for Analysisn Is the following system modifiable?这个系统具有适应性吗？ Background color of the user interface is changed merely by modifying a resource file.通过修改资源文件，可以改变界面的背景色 Dozens of components must be changed to accommodate a new data file format.必须修改许多组件才能适应新的文件格式n A reasonable answer is一个合理的答案：yes with respect to changing background color有，从改变背景色的角度来看no with respect to changing file format没有，从改变文件格式的角度来看 Qualities Are Too Vague for Analysisn Qualities only have meaning within a context.质量因素只在一定的上下文里才有意义n SAAM specifies context through scenarios.SAAM通过场景指定上下文 Scenariosn A scenario is a brief description of a stakeholders interaction with a system.场景就是一个角色与系统交互过程的简单描述n When creating scenarios, it is important to consider all stakeholders.建立场景的时候，一定要考虑到所有的角色Customer、User、Developer、Maintainer、Attackern The scenarios that are of most interest in a SAAM evaluation are change scenarios.SAAM最关心的是变化场景 Steps of a SAAM Evaluationn Identify and assemble stakeholders确认和召集角色n Develop and prioritize scenarios制定场景，并排好优先级n Describe candidate architecture(s)描述候选的体系结构n Classify scenarios as direct or indirect把场景分类为直接场景和间接场景n Perform scenario evaluation进行场景评估 n Reveal scenario interactions展现场景间的相互影响n Generate overall evaluation整体评估 Step 1: Identify and Assemble StakeholdersStakeholder InterestCustomer Schedule and budget; usefulness of system; meeting customers (or markets) expectationsEnd User Functionality, usabilityDeveloper Clarity and completeness ofarchitecture; high cohesion andlimited coupling of parts;clear interaction mechanisms Maintainer Maintainability; ability to locateplaces of change Step 1: Identify and Assemble StakeholdersStakeholder InterestSystem Administrator Ease in finding sources of operational problemsNetwork Administrator Network performance, predictabilityIntergrator Clarity and completeness ofarchitecture; high cohesion andlimited coupling of parts;clear interaction mechanisms Step 1: Identify and AssembleStakeholdersStakeholder InterestTester Integrated, consistent error handling; limited component coupling; high component cohesion; conceptual integrityApplication Builder Architectural clarity, completeness; interaction mechanisms; simple tailoring mechanismsRepresentative of the domain Interoperability Step 2: Stakeholders Develop andPrioritize Scenariosn Scenarios should be typical of the kinds of evolution that the system must support:场景应该是系统必须支持的各种演化的典型：functionalitydevelopment activitieschange activitiesn Scenarios should represent tasks relevant to all stakeholders.所有角色都应该能在场景中体现出来n Rule of thumb: 10-15 prioritized scenarios应该有10-15个优先的场景 Step 3: Describe CandidateArchitecturesn It is frequently necessary to elicit appropriate architectural descriptions.通常，对体系结构进行适当的描述是非常重要的n Structures chosen to describe the architecture will depend on the type of qualities to be evaluated.以我们需要的质量为依据，选择用来描述体系结构的结构 Step 4: Classify Scenariosn There are two classes of scenarios. Direct scenarios are those that can be executed by the system without modification.直接场景是那些不需要修改系统就能执行的场景 Indirect scenarios are those that require modifications to the system.间接场景是那些需要修改系统的场景n The classification depends upon both the scenario and the architecture.场景的类型因系统而异n For indirect scenarios we gauge the order of difficulty of each change: e.g. a person-day, person-week, person-month, person-year.对间接场景，我们要度量适应每个变化的难度（工作量） Step 5: Perform Scenario Evaluationn For each indirect scenario identify the components, data connections, control connections, and interfaces that must be added, deleted, or modified明确其组件、数据连结件、控制连结件和要被增加、删除或修改的接口 estimate the difficulty of modification估算修改的难度n Difficulty of modification is elicited from the architect and is based on the number of components to be modified and the effect of the modifications.修改的难度体现在被修改的组件个数和修改的效果 n A monolithic system will score well on this step, but not on next step.只有一个模块的系统在此项评估可以得到高分，但是 Step 6: Reveal Scenario Interactionsn When multiple indirect scenarios affect the same components, this could indicate a problem.当多个间接场景影响同一个组件时，可能引发问题 could be good, if scenarios are variants of each other可能是好事，当场景是彼此的变体n change background color to green n change background color to red could be bad, indicating a potentially poor separation of concerns可能是坏事，说明模块划分有问题n change background color to redn port system to a different platform Step 7: Generate Overall Evaluationn Not all scenarios are equal.场景生来不平等n The organization must determine which scenarios are most important.必须明确哪些场景是最重要的n Then the organization must decide as to whether the design is acceptable “as is” or if it must be modified.评审团得出结论，当前的体系结构设计可行，还是必须要修改 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