PSAMS: a communication protocol specification assessment and measurement system

An obstacle to the uses of software metrics and size models, which we have developed for measuring the complexity and maintainability of a communication protocol specified in Estelle and for estimating the size of its specification and implementation, is the time‐consuming effort in collecting the metrics. To address this problem, a software system called PSAMS (protocol specification assessment and measurement system) for automatically calculating the metrics and sizes of specification and implementation has been developed. This paper describes the design of PSAMS, which provides five functionalities for a communication protocol Estelle specification: exploring its specification, measuring its complexity, assessing its maintainability, estimating its specification size and estimating its implementation size. To demonstrate the usefulness of PSAMS, we have applied it to measure the complexity and maintainability of 10 communication protocol Estelle specifications; the measurement results and decision support information provided by each functionality are presented in this paper. With PSAMS, communication protocol designers and developers are able to assess the complexity of a communication protocol early in the specification stage and have information which helps them manage a communication software project better. Copyright © 2002 John Wiley & Sons, Ltd.     

形式描述技术在通信协议安全分析中的应用

讨论在通信协议安全分析中形式描述技术的使用方法。重点研究在协议模型的基础上建立层次化的协议攻击行为模型的方法,对所建模型进行形式化验证和脆弱性分析,根据验证和分析结果提出防护措施,设计安全方案。给出Petri网建模实例,提出形式描述技术在通信协议安全分析中的一些其他应用。     

Towards formal specification of a distributed computing system

Onboard spacecraft computing system is a case of a functionally distributed system that requires continuous interaction among the nodes to control the operations at different nodes. A simple and reliable protocol is desired for such an application. This paper discusses a formal approach to specify the computing system with respect to some important issues encountered in the design and development of a protocol for the onboard distributed system. The issues considered in this paper are concurrency, exclusiveness and sequencing relationships among the various processes at different nodes. A 6-tuple model is developed for the precise specification of the system. The model also enables us to check the consistency of specification and deadlock caused due to improper specification. An example is given to illustrate the use of the proposed methodology for a typical spacecraft configuration. Although the theory is motivated by a specific application the same may be applied to other distributed computing system such as those encountered in process control industries, power plant control and other similar environments.     

基于形式化规格说明的UML状态图提取

为了辅助软件开发者理解形式化规格说明,提出一种从B方法规格说明中提取UML状态图的方法。通过分析状态信息在规格说明中的表现形式,定义一系列精确的简单状态、状态迁移、复合迁移、分层状态和状态图通信等提取规则。借助状态变量表和状态迁移表,最终实现状态元素和状态关系的提取,并以此构造完整的UML状态图。实验结果验证了方法的正确性及有效性。     

The influence of formal representation on solution specification

The effectiveness and value of a notation is determined by how well its users are able to work with it. This paper reports upon an empirical study aiming at investigating the influence of employing the Z specification notation upon how users approach system development. The study illustrates how the desire to employ formality can have a significant influence upon preferred choice between different solution approaches. Despite the formal representation increasing the awareness of the characteristics of a given design problem, the notation is apparently detrimental in the subjects' consideration of good-quality generic solutions. The human factor issues of the notation need to be carefully considered and the notation should be embedded into a proper method if effective use is to be achieved.     

Comparative aspects of software complexity metrics and program modules — a multidimensional scaling approach

A multivariate statistical procedure called multidimensional scaling is used to study the relationship of various software complexity metrics and program modules. The program modules that make up a software system are analysed and their effects towards the overall characteristics of a software are viewed. This multidimensional scaling technique is applied to a sample data set. The scaling procedure clustered the similar and dissimilar software complexity metrics. Program modules with low complexity and few errors clustered together, while modules which were complex were isolated. This technique shows promise in the identification of complex modules that potentially contain disproportionate errors prior to the testing phase. The ability of the scaling techniques to cluster similar and dissimilar characteristics is explained and graphically presented.     

形式化规范在软件可靠性早期估计中的应用研究

随着软件的广泛应用,特别是软件在尖端领域的应用,软件可靠性成为一个非常重要的问题。形式化规范在软件可靠性研究中能够起到的作用是多方面的。本文针对非形式化统计使用测试的不足,结合已有的早期可靠性估计方法,设计了优化算法,并提出了即使在设计中采用了形式化规范仍然需要测试的结论。     

RSL在协议形式化描述中的应用研究

将RSL引入协议工程,探讨了对协议进行形式化描述的一条新途径。为RSL扩充了时间描述机制,讨论了基于两类基本模型（状态模型和进程模型）的协议描述方法及一般描述步骤。以示例方式给出了RIP路由简化算法的RSL形式化描述。与其他方法相比,扩充后的RSL描述能力强,描述手段灵活,能更有效地支持验证、测试等后续阶段的工作。     

A composite complexity approach for software defect modelling

An approach is proposed to develop defect models for software components based on a categorical multivariate regression analysis. This modelling technique is useful when the software components are sufficiently small so that the assumption of a continuous normally distributed defect distribution is not valid. Library unit aggregations from five Ada projects are analysed to yield a composite complexity measure which is a function of both software complexity characteristics and development environment characteristics. The probabilities of various numbers of defects are derived from this composite complexity measure. The probability distributions are used to calculate subsystem level defects which are then compared to the actual defects.     

Using a formal specification contractually

A commonly made criticism of formal methods is that they increase costs. Selective use of formal methods to define critical requirements can, however, lead to a significant decrease in lifecycle costs. In particular the economic and technical benefits of outsourcing the development of software can be fully realized and the cost of outsourcing slightly reduced by use of a formal specification. In this paper we describe a development in which a formal specification prepared by the customer formed part of the contract with the supplier. We conclude that this use of a formal specification can reduce risks and costs for all concerned and can help foster fruitful and co-operative relations in situations which are often fraught with confrontation.Published with the permission of the controller of Her Britannic Majesty's Stationery Office.     

Experience of using a lightweight formal specification method for a commercial embedded system product line

A simple specification method is introduced and the results of its application to a series of projects in Philips are reported. The method is principally designed to ensure that that every unusual scenario is considered in a systematic way. In practice, this has led to high-quality specifications and accelerated product development. While the straightforward tabular notation used has proved readily understandable to non-technical personnel, it is also a formal method, producing a model of system behaviour as a finite state machine. In this respect, the notation is unusual in being designed to preserve as far as possible a view of the overall system state and how this changes. The notation also features a constraint table which may be described as a kind of spreadsheet for invariants to help define the states of the system.

Measuring complexity in C++ application software

This paper concerns the use of design/source-code complexity metrics in analysing C++ software. It describes the use of one suite of object-oriented metrics published by Chidamber and Kemerer¹ to evaluate a commercial C++ application. It provides an interpretation and critique of these metrics, including the use of two traditional metrics (Cyclomatic Complexity² and Software Science³) in association with these object-oriented metrics. The evolution, over a two and a half year period, of one commercial grade C++ application comprising 114 classes with 25,000 lines of code is studied. The efforts consumed in bug fixes and enhancements are correlated with the complexity measures on a per class basis, and results are presented. These results are compared to those from other workers. The paper provides a detailed analysis of the practical strengths and weaknesses of the metrics suite in the light of experiences with its use. © 1998 John Wiley & Sons, Ltd.     

Structuring formal specifications—a lesson relearned

Specifications written in the formal specification language Z often make use of a form of decomposition that is novel to programmers. A published Z specification is rewritten using the form of decomposition familiar to programmers. Whenever decomposition is used, there must be some strategy for deciding what is to go in one component and what is to go in another. At the highest level, the strategy underlying the rewritten specification is the well-known strategy of separating user interface issues from deeper system functionality issues. The effectiveness of the strategy is put to a simple test by showing how a modification to the interface can be supported by a modification to only part of the specification. The conclusions drawn are that care over decomposition is important in specifications, just as it is in programs, and that lessons learned from programming about effective decomposition strategies can be applicable at the specification level, too. In particular, the lesson relearned is that it is important to separate information about a system's functionality from information about how this functionality is presented to users.     

构件适应和组装的形式化语义描述

构件适应技术是基于构件的软件工程中一个很难解决的问题,分析了三种构件适应结构的应用条件,采用了形式化语义的方法描述和推导了与构件以及构件适应相关的问题,根据构件描述与应用需求描述动态地选择不同的适应层次来适应构件,从被适应的构件描述中推导出复合构件的描述,为构件适应的形式化分析、组装正确性检验提供了保证,并列出了一些值得进一步研究的问题。