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考试的 Requirements Specification Languages* 要求规范语言* TH Tse and L. Pong* 钍和L.凤谢* Department of Computer Science 计算机科学系 The University of Hong Kong 香港的香港大学 Pokfulam Road 薄扶林道 Hong Kong 香港 ABSTRACT摘要We examine the features which are most desirable in requirements specification languages, and 我们研究的特点，是最可取的规范语言的要求， then use the framework to review six established languages: PSL, SADT, EDDA, SAMM, HOS and 然后使用该框架，检讨既定六个语言：PSL,SADT,EDDA,SAMM,HOS 和 RSL. RSL。 Keywords and phrases: Requirements specification, specification languages, systems development关键字和词组：要求规范，规范的语言，系统开发 CR Categories: D.2.1, F.3.1, K.6.3华润分类：D.2.1， F.3.1，K.6.3 1.1。INTRODUCTION简介A requirements specification for an information system is important for several reasons: It serves 一个信息系统的要求规范为重要的是有几个原因：它造福 as a means of communication between the user and the systems developer; it represents in a 作为一种手段，造福开发人员和用户之间的通信系统，它代表着一个 systematic fashion the current state of the real world, its problems and its future requirements; it 系统地未来的需求现状的真实世界，它的问题与它 enables the systems developer to turn real world problems into other forms which are more 使系统开发商把这些其他形式的世界更真实的问题为 manageable in terms of size, complexity, human understanding and computer processability; it serves 加工处理的计算机上规模，复杂性，人类认识和它服务 as the basis for the design, implementation, testing and maintenance of the target system. 作为系统的基础上的设计，实施，测试和维护的目标。 In order 为了 that all the objectives of a requirements specification be met, we need a powerful specification 所有的规范目标的要求得到满足，我们需要一个强大的规范 language. 语言。 Quite a number of authors (such as 9, 21, 13, 36, 38) have proposed independently the 不少的作者（如9，21，13，36，38提出独立的 desirable features of requirements specification languages. 规范语言理想的功能要求。 In Section 2 of this paper, we consolidate 在本文件第2节，我们巩固 these features and present them in the context of an engineering process. 这些特点，目前他们在工程过程中的一个。 Then, in Section 3, we use 然后，在第3节中，我们使用 the proposed features as the basis of an examination of some of the established research in 建立了研究，在所提出的一些特点的基础上的检验 specification languages. 规范语言。 2.2。DESIRABLE FEATURES OF A REQUIREMENTS SPECIFICATION LANGUAGE规范语言的一个理想的功能要求Information systems development can be conceived of as an engineering process. 信息系统的发展可以理解为一个工程过程。 A graphical 一个图形 representation is shown in Figure 1. 表示见图1。 We must first of all build a model, which is a small-scaled 我们必须首先建立一个模型，它是一个小规模 abstract representation of the real world. 抽象表现真实的世界。 All unnecessary details in the physical world which are 这些都是不必要的细节，物理世界 irrelevant to the engineering process are removed from the model, or in other words, ignored during 工程过程无关，从模型中删除，或者换句话说，在被忽略 Part of this research was done at the London School of Economics, University of London under a Commonwealth *研究部这样做是在伦敦经济学院，伦敦大学根据英联邦 Academic Staff Scholarship. 教学人员奖学金。 The research was also supported in part by a Hong Kong and China Gas Research Grant 该研究也支持部分由香港及中国天然气研究资助 and a University of Hong Kong Research and Conference Grant. 格兰特和香港大学的研究和会议。 Currently with IBM, Canada. *目前与IBM，加拿大。 1一Page 2第2页Tse and Pong谢和凤Requirements Specification Languages要求规范语言22the analysis stage. 分析阶段。 When a bridge or tunnel is planned between two nations, for instance, the political 当一个桥梁或隧道计划在两个国家，例如，政治 issues should best be dealt with by politicians and not form part of the engineers requirements 问题的最好方式是通过政治家，而不是形式上的要求部分工程师 specification. 规范。 If the resulting model is still too complex, further abstractions may be necessary, until the 如果得到的模型仍然过于复杂，可能需要进一步的抽象，直到 problem is reduced to a manageable size. 问题归结为一个管理的规模。 The model is then analysed and manipulated until a feasible 然后分析该模型是一个可行的和操作，直到 solution is found. 找到解决办法。 In engineering, diagrams and mathematics are often used because they have been 在工程，图表和数学却经常使用，因为他们已经 found to be more suitable for manipulation than verbal descriptions. 发现更合适的语言描述为操纵比。 One representation may have to 一个表示可能要 be transformed into another so that the most appropriate model for a given analysis can be used. 被转化成另一种，这样一个给定的最合适的分析模型都可以使用。 Diagrams, for instance, may have to be converted into equations. 图，例如，可能要转换成方程。 Finally, if the abstract solution is 最后，如果抽象的解决方案 accepted by the customer, a construction phase turns it into a real system. 客户所接受，变成一个施工阶段系统它变成现实。 In order for a requirements specification to be useful in systems development, seen as an 为了使发展的要求规格为有用的系统中，被视为 engineering process, the specification language must exhibit various features, each being relevant to 工程流程，规范的语言必须表现出的各种功能，每个被有关 one of the stages. 其中一个阶段。 These features will be highlighted in this section. 这些功能将被突出在这一节。 We recognise that there are authors who may object to having an engineers view of information 我们认识到，有作家谁可能反对有一个工程师的信息观 systems development. 系统的发展。 Examples are Checkland, Land and Mumford 5, 18, 23, who regard systems 切克兰德的例子是，土地和芒福德5，18，23，谁把系统 development as a human activity process. 发展作为人类活动的进 程。 They propose that emphasis should be made on such issues 他们建议，应强调对这些问题作出 as understanding the impacts of change, people-oriented design and user participation throughout the 为了解整个的变化，以人为本的设计和用户参与的影响 development process. 发展进程。 It would be interesting to study how our proposal for the desirable features of a 这将是有趣的研究如何为我们的建议是可取的特点 specification language fits into this alternative framework. 规范语言就属于这种替代的框架。 It is, however, beyond the scope of the 它是，但是，超出了其范围 present paper to do so. 本文这样做。 2.1 ABSTRACTION OF THE REAL WORLD2.1对现实世界的抽象A requirements specification language is the means by which users can make a model of the real 阿要求规范语言是手段，使用户能够真正模型的 world and specify its problems and requirements. 世界并指定其问题和要求。 It is the bridge between a development environment 这是环境发展之间的桥梁 and the users, including systems analysts, designers and end users. 和用户，包括系统分析师，设计师和最终用户。 We must ensure that this interface 我们必须确保该接口 is understandable to all concerned. 向所有关心是可以理解的。 The usual marketing phrase user-friendliness is a bit too vague 通常的营销语用户友好是一个有点含糊 to act as a useful guide. 作为一个有用的指导。 Instead, we consider it essential for the language to have the following 相反，我们认为有必要的语言有以下 properties: 属性： 2.1.1 USER FAMILIARITY OF THE SPECIFICATION LANGUAGE2.1.1规范语言用户熟悉性作者：It would be difficult for users to employ an entirely new requirements specification language 这将是用户难以雇用一个完全新的要求规范语言 because of several reasons. 由于几个原因。 (a) There is an inertial effect from the point of view of users. （一）有一个惯性效应的用户观的点。 They are not willing to try a new 他们不愿意尝试新的 method with which they are not familiar. 方法与他们不熟悉。 (b) From the management point of view, a well-tested methodology which has proven popularity （二）从管理角度证明流行的观点，一个行之有效的方法，其中有 tends to be more acceptable than a newly proposed technique. 更趋于技术比接受新建议。 It is more easy to recruit staff 这是更容易招聘工作人员 members who are trained and experienced in an established method. 谁是训练方法成员建立和经验丰富的一个。 It would be easier to 它会更容易 maintain standards if the same methodology were used throughout the company. 维持公司的标准，如果同样的方法使用了整个的。 Managers in 经理人 general find it safer to be old-fashioned than to try the latest innovation and regret it afterwards. 一般认为它更安全，是老式的，而不是尝试最新的创新和遗憾它之后。 22Page 3第3页Tse and Pong谢和凤Requirements Specification Languages要求规范语言3三As a result, practitioners are rather hesitant to use new tools which involve an unfamiliar formal 因此，从业者都比较犹豫，其中涉及新的工具使用不熟悉的正式 language 10, 20, 21. 语言10，20，21。 When we propose a new systems development environment, therefore, we 当我们提出一个新的系统开发环境，因此，我们 should not be inventing an entirely new language, with the hope that it will turn out to be the best in 不应该发明一种全新的语言，希望这一事件将是最好的 the world. 世界。 Instead, we should try to use a currently available specification language which has most 相反，我们应该尽量使用现有的规范语言，有最 of the desirable features and, more importantly, has proven popularity among practitioners. 对可取的特点，更重要的是，已经证明了从业人员的世俗性。 2.1.2 LANGUAGE STYLE2.1.2的语言特色(a) Textual Language（一）文本语言When we consider the use of a textual language for requirements specifications, two 当我们考虑两种语言的要求的规格，使用文本 possibilities arise: We may like either a natural language or a more formal programming-like 可能出现：我们可能喜欢任何一种自然语言或更正式的程序，如 language. 语言。 There is little doubt that natural languages give a better persuasive power and more 毫无疑问，自然语言提供更好的说服力，更 freedom of expression, especially in the initial phases of the system life cycle when a degree of 言论自由，尤其是在系统生命周期的最初阶段的程度时， uncertainty is involved. 涉及的不确定性。 It is also more natural to the average end user and hence improves the 它也更自然，普通的最终用户，从而提高了 user-understanding of a new situation. 用户了解新的形势。 Research workers in artificial intelligence, however, are 在人工智能的研究人员，但是， still trying very hard to make natural language understood by computer systems, and hence it is 还是很努力，使自然语言理解系统由计算机，因此它是 impossible currently to find a development environment which supports requirements 目前不可能找到一个开发环境，支持要求 specifications based on natural language. 基于自然语言规范。 On the other hand, requirements specified in a natural language may cause ambiguities, since 另一方面，语言中指定的必然要求可能会造成歧义，自 they may be interpreted differently by different people. 它们可能是由不同的人有不同的解释。 As pointed out by DeMarco 11 and 正如所指出的德马 科11 others, standard English prose is not suitable even for specifications which are processed 其他人，标准不规范英语散文适合即使被处理 manually. 手动。 Languages that have a better defined syntax and slightly more restrictive semantics 语言有一个更明确更严格的语法和语义略 would therefore be preferred. 因此将优先考虑。 These languages are more formal in nature and resemble a 这些语言是比较正规的性质，就象一座 programming language or a mathematical language. 编程语言或数学语言。 (b) Graphical Language（二）图形语言It is generally agreed that graphical representation of complex material is much more 人们普遍认为，复杂的图形表示材料更加 comprehensible than its textual counterpart. 理解比文字对应。 The reasons can be summarized as follows: 其原因可概括如下： Graphics is in two dimensions while text is in one dimension. 图形是一维的尺寸，而在两个文本。 The former gives an additional 前者给出了一个额外的 degree of freedom in presentation. 度表现自由英寸 Graphics is more useful in showing the hierarchical structure of complex systems and more 图形是在展示更多更实用的系统和复杂的层次结构 natural in describing parallelism. 在描述自然的并行性。 A person reading graphics can do so selectively, depending on the level of details required. 一个人的阅读选择图形可以这样做，取决于细节层次的需要。 If 如果 he reads text, he has to do so linearly. 他读的文本，他这样做的线性关系。 There is a limit to the number of concepts which can reasonably be held in the short-term 有一个限制举行的是数字的概念，可以合理的短期 memory of human mind 22 . 人类心灵的记忆22。 A person reading graphics can start off generally and go down to 一个人阅读图形可以开始普遍，深入 detail after some degree of familiarization. 经过一番详细的熟悉程度。 If one is reading text, then one has to start off with 如果一个人阅读的文本，然后一个人开始了与 the detail and abstract the skeleton concepts afterwards. 具体和抽象的概念，后来的骨架。 3三Page 4第4页Tse and Pong谢和凤Requirements Specification Languages要求规范语言44It should be noted, however, that graphical languages with too many symbols are not necessarily 应当指出的是，许多符号图形语言过多并不一定 comprehensible to end users. 理解到最终用户。 The graphics-based language must consist only of a relatively small 图形为基础的语言只能由一个相对小 number of easily understood symbols. 数容易理解的符号。 (c) Hybrid Languages（三）混合语言It is often impractical to define a requirements specification only in terms of a single 它往往是不切实际的要求，规范只定义在一个单一条款 graphical or textual language. 图形或文本语言。 For example, although graphical languages are better than textual 例如，虽然语言文字的图形比 languages in presenting an overview of a complex situation, textual languages are regarded as 情况复杂的语言概述在提交的，被视为文本语言 better tools for detailed description. 为更好的工具的详细描述。 Although formal languages have precise semantics, their 尽管正式的语言有精确的语义，其 meanings are often explained through natural languages. 通常意义来解释自然语言。 We need, therefore, a language which 我们需要，因此，语言， exists in more than one format. 存在于一个以上的格式。 A reasonable subset of the specification, at least at the higher 一个规范合理的子集，至少在较高 levels of abstraction, must exist both as formal and informal versions. 抽象层次的，必须同时存在正式和非正式的版本。 The specification must be 该规范必须 convertible from one form to another so that users, analysts, designers, implementors and 从一种形式转换到另一种让用户，分析师，设计师，实现者和 managers can communicate effectively. 管理人员可以有效沟通。 A person needs only to review the version most 一个人只需要审查的版本最 appropriate to his understanding and his needs. 适合他的理解和他的需要。 A formal one-to-one correspondence must be 一个正式的一对一的一一对应关系，必须 maintained among the various syntaxes of the specification language, so that there will not be any 坚持规范语言之间的各种语法的，所以不会有任何 error or dispute. 错误或争议。 2.1.3 COMPLEXITY2.1.3复杂性As suggested in 39 , complexity is the main barrier to the understanding of system problems. 为建议在39，复杂性是主要障碍问题的了解系统。 A 一 requirements specification language should therefore provide a means to improving the conceptual 因此，要求规范语言应该提供一种手段，改进的概念 clarity of the problems. 明晰的问题。 There are two ways of attaining this goal. 有两种途径实现这一目标。 (a) Separation of Logical and Physical Characteristics（一）分离逻辑和物理特性When we analyse the requirements of a system, we should distinguish between logical and 当我们分析一个系统的要求，我们要区分逻辑和 physical characteristics. 物理特性。 By logical characteristics we mean the essential features of the system 由逻辑特征是指对系统的基本特征 which must be satisfied in order to meet the users requirements, irrespective of the actual 必须满足，以满足用户的要求，不论实际 procedure or mechanism. 程序或机制。 They are also known as essential characteristics. 他们也被称为基本特征。 By physical 通过物理 characteristics we mean the way in which the system actually functions in the real world. 特征是指以何种方式，系统在现实世界的实际功能的。 A 一 typical example of the latter is a process which employs some specific tool or material, such as 后者典型的例子是一个过程，采用一些具体的工具或材料，如 photocopiers or microfilms. 复印机或缩微胶片。 In another example, we may encounter two independent tasks with 在另一个例子中，我们可能会遇到两个任务与独立 no data passing from one to the other, and yet they are performed in a definite sequence. 从一个没有数据传递到另一个人，但他们却在一定的顺序执行。 Such an 这样一 order of events is more likely to be due to political or historical issues not relevant to the system. 更多的是事件的顺序可能是由于政治或历史问题不相关的系统。 A requirements specification language must allow us to model logical and physical 阿要求规范语言必须允许我们的逻辑和物理模型 characteristics separately, in order to differentiate important issues from non-essentials. 特色另一方面，为了区分必需品与非重要问题。 For 对于 example, when we analyse a control system for operating a lift, we may like to exclude such 例如，当我们分析一个电梯控制系统的运作，我们要排除这种可能 physical features as colour, decor and lighting from our logical model. 逻辑模型的物理特征的颜色，从我们的装饰和照明。 In this way, the logical 这样，逻辑 model for the lift control system may be found to be equivalent to that of a disk control system, so 系统模型的电梯控制可能被认为相当于系统的一个磁盘的控制，因此 that any expertise in one design can be applied to the other. 设计专业知识，任何人可以应用到其他。 44Page 5第5页Tse and Pong谢和凤Requirements Specification Languages要求规范语言55(b) Multi-Level Abstraction（二）多层次抽象A hierarchical framework should be provided by the specification language to enable users to 分层框架应提供的规范语言，使用户能够 visualize a target system more easily. 可视化的目标体系更加容易。 It allows users to start conceptualizing the system at the 它允许用户在启动系统的构思 highest level of abstraction, and then to continue steadily downwards for further details. 最高抽象层次，然后继续稳步下调的进一步细节。 It allows 它允许 users to distinguish those parts of the target system relevant to a given context from those which 用户目标系统的部分区分了从这些相关的特定背景下的 are not. 不是。 Such a top-down approach frees users from embarking on unnecessary detail at a time 这种自上而下的方法可以让用户不必要的时间从着手进行详细的一 when they should be concerned only with an overall view of the target system. 当他们应该只关心一个目标系统的总体看法。 On the other hand, 另一方面， it allows certain parts of a system to be investigated in detail when other parts are not yet defined. 它允许定义的某些部分，系统在被调查的细节时，其他部分还没有。 To enable users to relate a requirements specification to real life problems, the specification 为了使用户能够给出一个现实生活需求规范的问题，规范 language should help them to refine the target system in a natural way. 语言应该帮助他们完善以自然的方式在目标系统的研究。 Target subsystems must 目标子系统必须 be as self-contained as possible. 作为独立的越好。 The interface between any two subsystems should be kept to a 各子系统之间的接口的任何两个应保持在一 minimum but defined explicitly. 最低但明确界定。 This will reduce complexity, avoid misunderstanding, and make 这将降低复杂性，避免误解，并 it possible for two subsystems to be analysed further by two different people. 这两个子系统可能要进一步分析由两个不同的人。 System modules 系统模块 created in this way can be reusable common components which are independent of the parent 这个方法创建可重用的通用组件是独立于母公司 modules that call them. 模块，给他们打电话。 Furthermore, sufficient mechanism should be build into the development 此外，应建立足够的机制纳入发展 environment to help users to check whether each refinement step is logically valid, so that each 环境，帮助用户检查是否每个步骤在逻辑上是有效的细化，使每 group of child modules exactly replace the relevant parent module. 儿童组的模块正是父模块取代有关。 2.1.4 MODIFIABILITY2.1.4可变性The requirements specification must be structured in such a way that the parts of a target system 规范的要求，必须在这样的结构方式，指标体系的一个部分 can be modified easily to cater for new user needs, technological updates and/or other changes in the 可以轻松地进行修改，修改应付新的用户需求，技术更新和/或其他方面的 environment. 环境。 It should cater not only for amendments by the original specifier, but also allow 它不仅要照顾没有说明原来的修正案的，但也让 modifications to be made by anyone who is assigned the task. 要作出修改，任何人谁被赋予的任务。 2.2 MANIPULATION OF REPRESENTATIONS2.2操纵陈述2.2.1 TOOLS FOR MANIPULATION2.2.1操作工具的(a) Formalism（一）形式主义In order to eliminate the problems of ambiguity during the construction and implementation 为了消除和实施建设过程中存在的问题歧义 of a target system, the requirements specification should be expressible in a precise notation with 目标系统，规范的要求，应以一种精确的符号可表达与 a unique interpretation. 一个独特的解释。 A formal framework must, therefore, be present. 一个正式的框架，因此必须在场。 It helps to reduce the 它有助于减少 probab