Formal analysis of the Shlaer-Mellor method: Towards a toolkit of formal and informal requirements specification techniques

In this paper, we define a number of tools that we think belong to the core of any toolkit for requirements engineers. The tools are conceptual and hence, they need precise definitions that lay down as exactly as possible what their meaning and possible use is. We argue that this definition can best be achieved by a formal specification of the tool. This means that for each semi-formal requirements engineering tool we should provide a formal specification that precisely specifies its meaning. We argue that this mutually enhances the formal and semi-formal technique: it makes formal techniques more usable and, as we will argue, at the same time simplifies the diagram-based notations.At the same time, we believe that the tools of the requirements engineer should, where possible, resemble the familiar semi-formal specification techniques used in practice today. In order to achieve this, we should search existing requirements specification techniques to look for a common kernel of familiar semi-formal techniques and try to provide a formalisation for these.In this paper we illustrate this approach by a formal analysis of the Shlaer-Mellor method for object-oriented requirements specification. The formal specification language used in this analysis is LCM, a language based on dynamic logic, but similar results would have been achieved by means of another language. We analyse the techniques used in the information model, state model, process model and communication model of the Shlaer-Mellor method, identify ambiguities and redundancies, indicate how these can be eliminated and propose a formalisation of the result. We conclude with a listing of the tools extracted from the Shlaer-Mellor method that we can add to a toolkit that in addition contains LCM as formal specification technique.     

高层建筑结构CAD系统的数据模式

用面向对象的分析方法对高层建筑结构CAD系统进行了分析,通过对基本对象及其之间关系,作用的抽象,运用面向对象的设计方法建立了高层建筑 基本对象模型,采用面向对象技术和关系数据库相结合的方法,构造和初步建立了高层建筑结构的工程数据库,能够较好地解决高层建筑结构集成化CAD系统的数据组织和管理问题。     

Object-oriented task analysis

The object-oriented approach has recently received much attention in MIS development. However, as yet little research has been reported on task analysis in the object-oriented paradigm. This paper describes an object-oriented method for task analysis. Three fundamental types of objects (task, user, and interface) engaged in task analysis are described. The association between these objects is then built through identifying the messages between the objects. A practical application of this method shows that it is useful for the analysis and design of a human-computer interface.     

基于面向对象的花边CAD系统的设计与具体实现

阐述了一个采用面向对象技术来设计刺绣ＣＡＤ系统的方法。通过对系统的分析,给出了系统的基本设计模型,确定了面向对象技术的基本元素－－对象,并对对象进行了详细设计。文章最后对系统进行了简单评价。     

可组态保安监控系统软件设计与实现

保安监控系统是一种根据应用情况需要灵活定制的系统,安对软件提出了高度的柔性可组态要求。本文运用面向对象的方法,在充分分析了系统对象和结构特点的基础上,设计了一种具有高度柔性的可组态监控系统软件体系结构,并描述了软件的实现方法和过程。     

汉字字形编辑器的面向对象实现技术

本文介绍了一个实用的采用面向对象技术实现的汉字字形编辑器(C Glyph Editor) 。首先介绍了类与其实例的设计思路,接着阐明了典型编辑操作的实现即系统中各对象的通讯机制,最后对设计字形编辑器时采用传统设计方法与面向对象技术进行了比较与分析。     

The active deallocation of objects in object-oriented systems

In object-oriented systems, it is oftern useful for objects to be allowed to carry out some action before they are deallocated. This can be done by defining a destroy method in the object's class, and arranging for the memory system to send a message invoking this method immediately before deallocating the object. This allows resources associated with the object to be returned to the system, limited cross-language garbage collection, and other, more complex, behaviour. During the execution of the destroy method it is possible for new references to objects to be created. Care must be taken that the garbage collection does not erroneously free such objects. Algorithms are presented to implement destroy methods in systems using reference counting and mark-scan garbage collection techniques. Properties that are desirable in such systems are also discussed.     

An approach to object identification, selection and specification in object-oriented analysis

When using current object-oriented methods in the development of computer-based information systems, problems frequently arise in the identification and specification of 'objects'. In this paper, these problems are discussed and an approach that draws upon interpretivist systems thinking is presented that, it is argued, may alleviate some of the problems. It is proposed that a method that has been developed specifically to aid the user and analyst to appreciate a perceived problem situation might provide a useful aid in the process of identifying objects from the situation which are meaningful to the user. [An attempt has been made to use terminology that is consistent with that used in object-oriented analysis. However, at times this terminology may be at variance with some of the interpretivist ideas put forward (e.g. the term 'user' is adopted, although the authors argue that the notion of 'client' is more appropriate to emphasize the increased involvement and responsibility of the 'user' in the approach advocated)]. The ability to achieve this is expected to facilitate the appropriate mapping of these meaningful objects into a technical specification through object-oriented methods and to encourage user acceptance of the resulting computer-based information system.     

面向对象的并行消息传递库的设计与实现分析

MPI是并行程序设计中广泛使用的一个消息传递库,虽然标准MPI-2定义了C 绑定,但它并不严格符合面向对象的观点。在分析各类已有面向对象消息传递系统的基础上,用C 设计并实现了一个面向对象的、易于传递对象(包括用户自定义类型和STL容器)的、MPI一致的、类型安全的、基于MPI的并行消息传递库,并给出了相应的使用实例及性能分析。     

数据库系统设计中的面向对象技术研究

基于面向对象技术的基本思想和开发过程,介绍了面向对象技术的实现方法.结合具体实例对面向对象技术在数据库系统结构设计和详细设计中的应用进行了详细的探讨,利用面向对象的数据库系统分析和设计方法,使用UML工具建立了具体的对象模型,给出了一种比较通用的数据库系统开发模式.使用该模式设计的系统重用性好,且易于维护,从而有效提高了数据库系统的开发质量.     

Observable behavior of distributed systems: Component reasoning for concurrent objects

Distributed and concurrent object-oriented systems are difficult to analyze due to the complexity of their concurrency, communication, and synchronization mechanisms. Rather than performing analysis at the level of code in, e.g., Java or C++, we consider the analysis of such systems at the level of an abstract, executable modeling language. This language, based on concurrent objects communicating by asynchronous method calls, avoids some difficulties of mainstream object-oriented programming languages related to compositionality and aliasing. To facilitate system analysis, compositional verification systems are needed, which allow components to be analyzed independently of their environment. In this paper, a proof system for partial correctness reasoning is established based on communication histories and class invariants. A particular feature of our approach is that the alphabets of different objects are completely disjoint. Compared to related work, this allows the formulation of a much simpler Hoare-style proof system and reduces reasoning complexity by significantly simplifying formulas in terms of the number of needed quantifiers. The soundness and relative completeness of this proof system are shown using a transformational approach from a sequential language with a non-deterministic assignment operator.     

面向对象的流程工业系统有向无环图建模

提出流程工业系统中有向无环图的面向对象的建模方法。介绍使用面向对象的技术对流程工业系统模进行建模的关键要素的技巧,定义描述流程工业系统中有向无环图模型的建模机制,扩展流程工业系统模型所具有的特性。以流程工业系统出现异常时的诊断实例说明系统模型解决问题的有效性。     

WCET分析中面向对象程序多态性问题的解决方法

用面向对象建模语言(如统一建模语言UML)设计并用面向对象程序设计语言(如C )实现实时系统是实时系统开发领域的一个趋势,但面向对象的主要特征(如多态性)却使程序最差情况执行时间(Worst-Case ExecutionTi me,WCET)更加难以分析。本文通过把UML设计信息引入WCET分析来解决此问题。考虑到UML关联关系描述了两个或多个具体类之间的对应关系,因此本文要求指定关联角色的多重性,并假定能够建立关联关系与其在程序中表示的对应关系。在已知关联角色多重性的基础上,本文计算特定循环的执行计数并确定在超(虚)类调用位置上每个具体类的对象个数,该循环使用超类变量遍历统一表示的关联角色对象。通过和Corti等人方法的结合,本文方法能够自动计算具有多态性特征的面向对象程序的WCET。实验结果表明,本文研究的情形在面向对象程序中普遍存在。     

一种Agent数据库系统框架及其规则并行算法

面向对象方法描述的对象是被动的,与主动机制存在矛盾,不能很好地定义分布式主动数据库中对象的功能和特性.分布式主动数据库中的主动规则还带来了终止性、合流性的问题.首先分析面向对象方法的局限性,将Agent技术、分布式数据库、主动数据库相结合,给出一种面向Agent的分布式主动数据库系统框架.然后在这个框架基础上,提出扩展事件规则图方法和改进的Coffman-Graham规则并行算法,并分析它们的性能.分析结果表明,前者在一定程度上解决了数据库系统的终止性问题,后者在保持合流性的基础上提高了规则并行处理效率.这个框架对研究Agent技术在分布式主动数据库中的应用有一定的启示.     

Scenario-based multitasking for real-time object-oriented models

Contemporary embedded systems quite often employ extremely complicated software consisting of a number of interrelated components, and this has made object-oriented design methodologies widely used in practice. To implement an object-oriented model in given target hardware, it is imperative to derive a set of tasks from the designed objects. This process of determining tasks and the events they handle greatly influences the real-time performance of the resultant system including response times and real-time guarantees. However, the innate discrepancies between objects and tasks make this exceedingly difficult, and many developers are forced to find their task sets through trial and error. In this paper, we propose Scenario-based Implementation Synthesis Architecture (SISA), an architecture consisting of a method for deriving a task set from a given object-oriented model and the development tools and run-time system architecture to support the method. A system developed with SISA guarantees the optimal response time for each event while deriving the smallest possible number of tasks. We have fully implemented SISA by extending the RoseRT development tool and applied it to an existing industrial PBX (private branch exchange) system. The experimental results show that SISA outperforms the best known conventional techniques by reducing maximum response times an average of 30.3%.     

面向实体对象的战场环境仿真系统研究

针对战场环境仿真系统中地理数据与其可视化方法协调管理困难的问题，引入面向对象技术建立实体对象，并采用面向对象地理空间数据库来存储实体对象。分析了面向实体对象的战场环境仿真系统的总体结构，建立了实体对象的仿真模型，研究了场景生成、场景漫游等技术，为该战场环境仿真系统的最终实现奠定了基础。     

对面向对象概念建模方法用于系统开发的一些思考

从方法学的角度对面向对象思想方法进行了评述,讨论了面向对象方法的局限性。论文指出面向对象思想方法并非消除系统开发的实质性困难的万能方法。作为系统集成开发策略的一方面,面向对象思想方法应该与其它方法互相协调。文章最后还讨论了面向对象方法在描述问题域时的不足。     

A New Method of Systemological Analysis Coordinated with the Procedure of Object-Oriented Design. II

The paper presents the results of development of an object-oriented systemological method used to design complex systems. A formal system representation, as well as an axiomatics of the calculus of systems as functional flow-type objects based on a Node-Function-Object class hierarchy are proposed. A formalized NFO/UFO analysis algorithm and CASE tools used to support it are considered.     

A practical approach to the design of concurrency in object-oriented systems

Object-oriented software development methods deal with concurrency according to either the implicit concurrency model or the explicit concurrency model. In the implicit model, the objects themselves have concurrent execution capabilities whereas in the explicit model, objects are encapsulated inside processes, the latter providing concurrent execution capabilities. Both models have their advantages and disadvantages. In this paper, we propose applying the implicit model only while conducting object-oriented analysis and then switching over to the explicit model in the design phase. The implicit model naturally fits the analysis phase because the resulting models of the software system will be based on objects—the important concepts of the application—not the issues of how concurrency is implemented. A switch over to the explicit model in the design phase achieves smooth integration with already existing software consisting of processes—which is the main constraint in many industrial applications. This paper presents in detail a systematic solution for the switch over between the concurrency models that applies for soft real-time systems and demonstrates it by a simplified example from a real telecommunication project. Any object-oriented method not yet dealing with concurrency issues can easily integrate the solution. ©1997 John Wiley & Sons, Ltd.