Maintainability and safety indicators at design stage for mechanical products

With the industrial products competition, reliability, maintainability and safety are key characteristics for availability improvement. This is mainly true in industries like automotive, aeronautic, or NC machines tools. Therefore, it is crucial to predict these characteristics as soon as possible before the manufacturing starts. This paper presents an approach to provide indicators for maintainability and safety prediction at early stage of design. The assessment procedure uses the product CAD 3D model and an associated semantic matrix gathering information on the product components criticality and reliability. Using this information we calculate indicators for the product maintainability and safety. An academic application is developed to illustrate our approach and point out the interaction between maintainability and safety constraints to determine suitable solution. In conclusion, we state on possible extensions of this approach for evaluating other product lifecycle characteristics and we give guidelines on the implementation aspects.     

Model-driven assessment of system dependability

Designers of complex real-time systems need to address dependability requirements early on in the development process. This paper presents a model-based approach that allows developers to analyse the dependability of use cases and to discover more reliable and safe ways of designing the interactions of the system with the environment. The hardware design and the dependability of the hardware to be used also needs to be considered. We use a probabilistic extension of statecharts to formally model the interaction requirements defined in the use cases. The model is then evaluated analytically based on the success and failure probabilities of events. The analysis may lead to further refinement of the use cases by introducing detection and recovery measures to ensure dependable system interaction. A visual modelling environment for our extended statecharts formalism supporting automatic probability analysis has been implemented in AToM³, A Tool for Multi-formalism and Meta-Modelling. Our approach is illustrated with an elevator control system case study.

基于用例模型的面向对象需求分析

面向对象方法正在逐渐取代传统的方法,日益成为当今软件工程领域的主流方法。在系统需求设计方法中用例模型已成为获取系统需求的主要技术,通过用例模型的建立和对用例的分析软件开发者可以准确地了解用户需求和系统功能。它是用户和软件开发者一起剖析系统需求的关键一步,可以推动需求分析后各阶段的开发工作。     

An experimental study on the conversion between IFPUG and UCP functional size measurement units

The use of functional size measurement （FSM） methods in software development organizations is growing during the years. Also, object oriented （OO） techniques have become quite a standard to design the software and, in particular, Use Cases is one of the most used techniques to specify functional requirements. Main FSM methods do not include specific rules to measure the software functionality from its Use Cases analysis. To deal with this issue some other methods like Kramer＇s functional measurement method have been developed. Therefore, one of the main issues for those organizations willing to use OO functional measurement method in order to facilitate the use cases count procedure is how to convert their portfolio functional size from the previously adopted FSM method towards the new method. The objective of this research is to find a statistical relationship for converting the software functional size units measured by the International Function Point Users Group （IFPUG） function point analysis （FPA） method into Kramer-Smith＇s use cases points （UCP） method and vice versa. Methodologies for a correct data gathering are proposed and results obtained are analyzed to draw the linear and non-linear equations for this correlation. Finally, a conversion factor and corresponding conversion intervals are given to establish the statistical relationship.     

Use cases – Yesterday,today, and tomorrow

To my knowledge, no other software engineering language construct as significant as use cases has been adopted so quickly and so widely among practitioners. I believe this is because use cases play a role in so many different aspects of software engineering.Although I first used the term in 1986, I had actually been working on and evolving the concept of use cases since 1967. So many people have asked me how I came up with this concept that I decided to write this article to explain the origins and evolution of use cases. Ill also summarize what they have helped us achieve so far, and then suggest a few improvements for the future.     

Towards developing consistent misuse case models

Secure software development should begin at the early stages of the development life cycle. Misuse case modeling is a technique that stems from traditional use case modeling, which facilitates the elicitation and modeling functional security requirements at the requirements phase. Misuse case modeling is an effective vehicle to potentially identify a large subset of these threats. It is therefore crucial to develop high quality misuse case models otherwise end system developed will be vulnerable to security threats. Templates to describe misuse cases are populated with syntax-free natural language content. The inherent ambiguity of syntax-free natural language coupled with the crucial role of misuse case models in development can have a very detrimental effect. This paper proposes a structure that will guide misuse case authors towards developing consistent misuse case models. This paper also presents a process that utilizes this structure to ensure the consistency of misuse case models as they evolve, eliminating potential damages caused by inconsistencies. A tool was developed to provide automation support for the proposed structure and process. The feasibility and application of this approach were demonstrated using two real-world case studies.     

Clarifying the semantics of value in use cases through Jackson's Problem Frames

Use cases constitute a popular technique to problem analysis, partly due to their focus on thinking in terms of the user needs. However this is not a guarantee for discovering all the subproblems that compose the structure of a given software problem. Moreover, a rigorous application of the technique requires a previous consensus about the meaning of I. Jacobson's statement “a use case must give a measurable value to a particular actor” (The Rational Edge, March 2003). This paper proposes a particular characterisation of the concept of “value” with the purpose of problem structuring. To this aim we base on the catalogue of frames for real software problems proposed by M. Jackson (Problem Frames, 2001) and we reason about what could be valuable for the user on each problem class. We illustrate our technique with the analysis of a web auction problem.     

浅议PDM环境下维修性信息模型的构建

该文根据产品数据管理(PDM)技术的特点,在产品信息模型的基础上,分析了维修性信息的构成与分类,采用面向对象技术初步建立了基于PDM环境的产品维修性信息模型,并简要阐述了建立这种信息模型的现实意义。     

Designing with scenarios: A critical review of current research and practice

There is a great deal of requirements engineering specifically, and information systems development research in general, in the area of scenarios as the ‘vocabulary’ for discussing and characterising designs for new artefacts. This is partly due to opening up the design process to a variety of participants in a project, and making explicit their ways of working, thinking and interactions with the design products. Scenarios, being concrete, and easy to understand and use, provide the means to describe the design vocabulary. They are used to focus on episodic cases, exchange ideas and thoughts about them effectively, and generally describe requirements and designs for a new artefact from the user’s perspective. In this paper, we review the effectiveness of the current state-of-practice in scenario-based approaches. The objective of this evaluation exercise is to define the requirements for improved ‘by scenario’ approaches to cope with requirements and designs for developing new artefacts.     

基于改善系统可维护性的软件设计优化与实现

维护是软件生命周期的一个重要阶段。软件的可维护性是构成软件质量的一个重要方面,直接决定了在软件系统或产品上需要投入 多大的成本与精力。当前,软件的可维护性越来越得到业界的重视,并逐渐成为衡量软件系统或产品是否成功的一个重要标志。人们对于软 件可维护性的分析与研究的热情也越来越高,期望能找到软件系统可维护性提高和优化的方法。从理论而言,研究能够从组成软件生命周期 的各个阶段入手,文章着眼于软件设计阶段,从软件设计的角度对软件的可维护性的提高与优化进行分析探讨.并针对一个具体项目给出相 关解决方案。     

基于CBR和RBR的维修性设计技术智能化

结合维修性设计过程分析和人类处理问题的思维方式,依据维修性设计技术的两大指导文献(《维修性设计准则》与《维修性设计技术案例汇编》),分析了RBR和CBR技术的优缺点,给出了基于RBR和CBR混合推理的维修性设计技术智能化的框架结构。     

UML中的用例建模

UML是目前面向对象程序设计中的一种标准的建模技术。在UML中,建立用例模型的作用在于捕获高层次的,以用户为中心的系统功能需求。本文在介绍UML的基础上,通过实例详细探讨了在UML中正确建立、使用用例模型的策略。     

Simplifying effort estimation based on Use Case Points

Context

The Use Case Points (UCP) method can be used to estimate software development effort based on a use-case model and two sets of adjustment factors relating to the environmental and technical complexity of a project. The question arises whether all of these components are important from the effort estimation point of view.

Objective

This paper investigates the construction of UCP in order to find possible ways of simplifying it.

Method

The cross-validation procedure was used to compare the accuracy of the different variants of UCP (with and without the investigated simplifications). The analysis was based on data derived from a set of 14 projects for which effort ranged from 277 to 3593 man-hours. In addition, the factor analysis was performed to investigate the possibility of reducing the number of adjustment factors.

Results

The two variants of UCP - with and without unadjusted actor weights (UAW) provided similar prediction accuracy. In addition, a minor influence of the adjustment factors on the accuracy of UCP was observed. The results of the factor analysis indicated that the number of adjustment factors could be reduced from 21 to 6 (2 environmental factors and 4 technical complexity factors). Another observation was made that the variants of UCP calculated based on steps were slightly more accurate than the variants calculated based on transactions. Finally, a recently proposed use-case-based size metric TTPoints provided better accuracy than any of the investigated variants of UCP.

Conclusion

The observation in this study was that the UCP method could be simplified by rejecting UAW; calculating UCP based on steps instead of transactions; or just counting the total number of steps in use cases. Moreover, two recently proposed use-case-based size metrics Transactions and TTPoints could be used as an alternative to UCP to estimate effort at the early stages of software development.     

On the relationship of concern metrics and requirements maintainability

Context

Maintainability has become one of the most essential attributes of software quality, as software maintenance has shown to be one of the most costly and time-consuming tasks of software development. Many studies reveal that maintainability is not often a major consideration in requirements and design stages, and software maintenance costs may be reduced by a more controlled design early in the software life cycle. Several problem factors have been identified as harmful for software maintainability, such as lack of upfront consideration of proper modularity choices. In that sense, the presence of crosscutting concerns is one of such modularity anomalies that possibly exert negative effects on software maintainability. However, to the date there is little or no knowledge about how characteristics of crosscutting concerns, observable in early artefacts, are correlated with maintainability.

Objective

In this setting, this paper introduces an empirical analysis where the correlation between crosscutting properties and two ISO/IEC 9126 maintainability attributes, namely changeability and stability, is presented.

Method

This correlation is based on the utilization of a set of concern metrics that allows the quantification of crosscutting, scattering and tangling.

Results

Our study confirms that a change in a crosscutting concern is more difficult to be accomplished and that artefacts addressing crosscutting concerns are found to be less stable later as the system evolves. Moreover, our empirical analysis reveals that crosscutting properties introduce non-syntactic dependencies between software artefacts, thereby decreasing the quality of software in terms of changeability and stability as well. These subtle dependencies cannot be easily detected without the use of concern metrics.

Conclusion

The correlation provides evidence that the presence of certain crosscutting properties negatively affects to changeability and stability. The whole analysis is performed using as target cases three software product lines, where maintainability properties are of upmost importance not only for individual products but also for the core architecture of the product line.     

A harmonised model for safety assessment and certification of safety-critical systems in the transportation industries

This paper describes a model for the assessment and certification of safety-critical programmable electronic systems in the transportation industries. The proposed model is founded on the significant commonalities between emerging international safety-related standards in the automotive, railway and aerospace industries. It contains a system development and a safety assessment process which rationalise and unify the common requirements among the standards in these areas. In addition, it defines an evolutionary process for the development of the system’s safety case. The safety case process shows how the evidence produced in the progression of safety assessment can be structured in order to form an overall argument about the safety of the system. We conclude that it is possible to use this model as the basis of a generic approach to the certification of systems across the transportation sector.