A novel requirement analysis approach for periodic control systems

Periodic control systems (PCSs) are widely used in real-time embedded system domain. However, traditional manual requirement analysis assumes the expert knowledge, which is laborious and error-prone. This paper proposes a novel requirement analysis approach, which supports the automated validation of the informal requirement specifications. Based on the normalized initial requirement documents, our approach can construct an intermediate SPARDL model with both formal syntax and semantics. To check the overall system behaviors, our approach can transform the SPARDL models into executable code for simulation. The derived prototype simulator from SPARDL models enables the testing-based system behavior validation. Moreover, our approach enables the analysis of the dataflow relations in SPARDL models. By revealing input/output and affecting relations, our dataflow analysis techniques can help software engineers to figure out the potential data dependencies between SPARDL modules. This is very useful for the module reuse when a new version of the system is developed. A study of our approach using an industry design demonstrates the practicality and effectiveness of our approach.     

MOBMAS: A methodology for ontology-based multi-agent systems development

Ontologies offer significant benefits to multi-agent systems: interoperability, reusability, support for multi-agent system (MAS) development activities (such as system analysis and agent knowledge modeling) and support for MAS operation (such as agent communication and reasoning). This paper presents an ontology-based methodology, MOBMAS, for the analysis and design of multi-agent systems. MOBMAS is the first methodology that explicitly identifies and implements the various ways in which ontologies can be used in the MAS development process and integrated into the MAS model definitions. In this paper, we present comprehensive documentation and validation of MOBMAS.     

ASM-based formal design of an adaptivity component for a Cloud system

The request of formal methods for the specification and analysis of distributed systems is nowadays increasing, especially when considering the development of Cloud systems and Web applications. This is due to the fact that modeling languages currently used in these areas have informal definitions and ambiguous semantics, and therefore their use may be unreliable. Thanks to their mathematical foundation, formal methods can guarantee rigorous system design, leading to precise models where requirements can be validated and properties can be assured, already at the early stages of the system development. In this paper, we present a rigorous engineering process for distributed systems, based on the Abstract State Machines (ASM) formal method. We rely on the foundational notions of ASM ground model and model refinement to obtain a precise model for a client-server application for Cloud systems. This application has been proposed to tackle the problem of making Cloud services usable to different end-devices by adapting on-the-fly the content coming from the Cloud to the different devices contexts. The ASM-based modeling process is supported by a number of validation and verification activities that have been exploited on the component under development to guarantee consistency, correctness, and reliability properties.     

Logical Object as a Basis of Knowledge Based Systems

This paper presents a framework called logical knowledge object (LKO),which is taken as a basis of the dependable development of knowledge based systems(KBSs).LKO combines logic programming and object-oriented programming paradigms,where objects are viewed as abstractions with states,constraints,behaviors and inheritance.The operational semantics defined in the style of natural semantics is simple and clear.A hybrid knowledge representation amalgamating rule,frame,semantic network and blackboard is available for both most structured and flat knowledge.The management of knowledge bases has been formally specified.Accordingly,LKO is well suited for the formal representation of knowledge and requirements of KBSs.Based on the framework,verification techniques are also explored to enhance the analysis of requirement specifications and the validation of KBSs.In addition,LKO provides a methodology for the development of KBSs,applying the concepts of rapid prototyping and top-down design to deal with changing and incomplete requirements,and to provide multiple abstract models of the domain,where formal methods might be used at each abstract level.     

Change impact analysis for requirements: A metamodeling approach

ContextFollowing the evolution of the business needs, the requirements of software systems change continuously and new requirements emerge frequently. Requirements documents are often textual artifacts with structure not explicitly given. When a change in a requirements document is introduced, the requirements engineer may have to manually analyze all the requirements for a single change. This may result in neglecting the actual impact of a change. Consequently, the cost of implementing a change may become several times higher than expected.ObjectiveIn this paper, we aim at improving change impact analysis in requirements by using formal semantics of requirements relations and requirements change types.MethodIn our previous work we present a requirements metamodel with commonly used requirements relation types and their semantics formalized in first-order logic. In this paper the classification of requirements changes based on structure of a textual requirement is provided with formal semantics. The formalization of requirements relations and changes is used for propagating proposed changes and consistency checking of proposed changes in requirements models. The tool support for change impact analysis in requirements models is an extension of our Tool for Requirements Inferencing and Consistency Checking (TRIC).ResultsThe described approach for change impact analysis helps in the elimination of some false positive impacts in change propagation, and enables consistency checking of changes.ConclusionWe illustrate our approach in an example which shows that the formal semantics of requirements relations and change classification enables change alternatives to be proposed semi-automatically, the reduction of some false positive impacts and contradicting changes in requirements to be determined.     

Experiences using lightweight formal methods for requirementsmodeling

The paper describes three case studies in the lightweight application of formal methods to requirements modeling for spacecraft fault protection systems. The case studies differ from previously reported applications of formal methods in that formal methods were applied very early in the requirements engineering process to validate the evolving requirements. The results were fed back into the projects to improve the informal specifications. For each case study, we describe what methods were applied, how they were applied, how much effort was involved, and what the findings were. In all three cases, formal methods enhanced the existing verification and validation processes by testing key properties of the evolving requirements and helping to identify weaknesses. We conclude that the benefits gained from early modeling of unstable requirements more than outweigh the effort needed to maintain multiple representations     

Generating Natural Language specifications from UML class diagrams

Early phases of software development are known to be problematic, difficult to manage and errors occurring during these phases are expensive to correct. Many systems have been developed to aid the transition from informal Natural Language requirements to semi-structured or formal specifications. Furthermore, consistency checking is seen by many software engineers as the solution to reduce the number of errors occurring during the software development life cycle and allow early verification and validation of software systems. However, this is confined to the models developed during analysis and design and fails to include the early Natural Language requirements. This excludes proper user involvement and creates a gap between the original requirements and the updated and modified models and implementations of the system. To improve this process, we propose a system that generates Natural Language specifications from UML class diagrams. We first investigate the variation of the input language used in naming the components of a class diagram based on the study of a large number of examples from the literature and then develop rules for removing ambiguities in the subset of Natural Language used within UML. We use WordNet, a linguistic ontology, to disambiguate the lexical structures of the UML string names and generate semantically sound sentences. Our system is developed in Java and is tested on an independent though academic case study.     

Exception representation and management in open multi-agent systems

One of the major issues in dealing with exceptions in open multi-agent systems (MAS) is lack of uniform representation of exceptions and their shared semantics. In the absence of a uniform framework different business organizations may use different representations for the same exception or may interpret the same exception in different ways. In order to address this issue we apply an ontological approach as a uniform way of representing and interpreting exceptions in cross-organizational settings. This helps agents from different organizations interpret exceptional situations in an unambiguous way and exchange exception related information using standard structures. We believe that an exception ontology along with a domain ontology increases the open MAS reliability and also enhances its fault tolerance capability. The proposed ontology is built using the ontological support provided by the JADE agent framework and exception diagnoses agents are implemented using the JACK™ agent framework.     

一种支持多视点方法的自动需求建模

需求建模是需求工程的关键一环,以基于本体的需求获取和分析为背景,尝试将多视点方法应用到基于本体的需求建模过程中,从多个视点出发在软件工具的协助下对需求描述进行自动需求建模,从而提高需求模型的完整性.同时给出一种视点描述方法,用于对自动建模过程中使用的视点进行形式化定义.     

Formal methods for verification and validation of partial specifications: A case study

This paper describes our work exploring the suitability of formal specification methods for independent verification and validation (IV&V) of software specifications for large, safety-critical systems. An IV&V contractor often has to perform rapid analysis on incomplete specifications, with no control over how those specifications are represented. Lightweight formal methods show significant promise in this context, as they offer a way of uncovering major errors without the burden of full proofs of correctness. We describe a case study of the use of partial formal models for IV&V of the requirements for Fault Detection Isolation and Recovery on the space station. We conclude that the insights gained from formalizing a specification are valuable, and it is the process of formalization, rather than the end product, that is important. It was only necessary to build enough of the formal model to test the properties in which we were interested. Maintenance of fidelity between multiple representations of the same requirements (as they evolve) is still a problem, and deserves further study.     

Using formal methods with SysML in aerospace design and engineering

Maintaining design consistency is a critical issue for macro-level aerospace development. The inability to maintain design consistency is a major contributor to cost and schedule overruns. By embedding The Systems Modeling Language (SysML) within a formal logic, formal methods can be used to maintain consistency as a design evolves. SysML, provided with a formal semantics, enables engineers to employ reasoning in the course of a typical model-based development process. Engineers can make use of formal methods within the context of current engineering practice and tools without needing to have special formal methods training. As component subsystems are introduced to refine a design, their assumptions are checked against current assumptions. If new assumptions do not introduce inconsistency, they are added to the model assumptions. If the assumptions render the design inconsistent, they are detected which minimizes potential rework. SysML has a demonstrated capability for top-to-bottom design refinement for large-scale aerospace systems. SysML does not have a formal logic-based semantics. The logical formalism within which SysML is embedded matches the informal semantic of SysML closely. The approach to integrating formal methods with SysML is illustrated with a typical macro-level aerospace design task. The design process produces a design solution which provably satisfies the top level requirements. The example provides evidence that coupling formal methods with SysML can realistically be applied to solve aerospace development problems. The approach results from a number of detailed design trades employing a model-based system development process which used SysML as the model integration framework.     

Proving the shalls

Incomplete, inaccurate, ambiguous, and vola-tile requirements have plagued the software industry since its inception. The convergence of model-based development and formal methods offers developers of safety-critical systems a powerful new approach to the early validation of requirements. This paper describes an exercise conducted to determine if formal methods could be used to validate system requirements early in the lifecycle at reasonable cost. Several hundred functional and safety requirements for the mode logic of a typical flight guidance system were captured as natural language “shall” statements. A formal model of the mode logic was written in the RSML^−e language and translated into the NuSMV model checker and the PVS theorem prover using translators developed as part of the project. Each “shall” statement was manually translated into a NuSMV or PVS property and proven using these tools. Numerous errors were found in both the original requirements and the RSML^−e model. This demonstrates that formal models can be written for realistic systems and that formal analysis tools have matured to the point where they can be effectively used to find errors before implementation. This project was partially funded by the NASA Langley Research Center under contract NCC1-01001 of the Aviation Safety Program.     

On the use of a formal requirements engineering language: The Generalized Railroad Crossing Problem

In this paper, we report on the use of theAlbert II requirements specification language through the handling of the Generalized Railroad Crossing case study. This formal language is based on an ontology of concepts used for capturing requirements inherent in real-time, distributed systems. Because of itsnaturalness, the language supports a direct mapping of customers’ informal needs onto formal statements, without having to introduce artificial elements. The language is founded on a formal framework (real-time temporal logic) which supports the reasoning process of the analyst during the elaboration of the specification. Such support for the reasoning is illustrated in the context of a goal-oriented approach adopted for the elaboration of the case study.     

Identification of ontologies to support information systems development

Ontologies can provide many benefits during information systems development. They can provide domain knowledge to requirement engineers, are reusable software components for web applications or intelligent agent developers, and can facilitate semi-automatic model verification and validation. They also assist in software extensibility, interoperability and reuse. All these benefits critically depend on the provision of a suitable ontology (ies). This paper introduces a semantically-based three stage-approach to assist developers in checking the consistency of the requirements models and choose the most suitable and relevant ontology (ies) for their development project from a given repository. The early requirements models, documented using the i^⁎ language, are converted to a retrieval ontology. The consistency of this retrieval ontology is then checked before being used to identify a set of reusable ontologies that are relevant for the development project. The paper also provides an initial validation of each of the stages.     

一个机载软件需求形式化建模与分析实例研究

现代民机机载软件系统的功能与复杂度在快速增长的同时还必须满足更严格的安全标准, 使得在机载软件需求层级必须进行诸如一致性、完整性等分析与验证成为重要的挑战. 工作基于一个自主设计实现的面向机载软件自然语言需求形式化建模与分析工具平台(ART)展开对座舱显控软件子系统(EICAS)需求的建模与分析, 包括: ART工具平...     

Formal Specifications of User Requirements

There is a wide gap between informal requirements and a formal object-oriented specification. To help bridge this gap, we propose that a formal and executable user-centred model should be constructed initially. The user-centred model, which specifies the behaviour that the environment expects from the system, is expressed in terms of agent views and gives very early feedback to the requirements' capture process. Once the user-centred model has been validated with respect to the environment, it can be used as a step in the construction and validation of the formal object-oriented specification.     

Telecommunications service development: A design methodology and its intelligent support

This paper describes a development life cycle for telecommunications services, emphasizing requirements capture, formal specification and validation. The service is developed along the three dimensions of the methodology: refinement, completeness and formality, aiming for a complete, consistent and formally specified service definition. The described methodology can be integrated into currently existing development life cycles which employ formal methods for service creation. Active support for the proposed life cycle is provided by a novel expert system called Requirements Assistant for Telecommunications Services (RATS), currently under development. It actively helps during requirements acquisition and early analysis, and encourages specification reuse with the help of a semi-automated negotiation process. The RATS tool advises the service developer during all stages of the service development, and on different levels of abstraction, and provides requirements management facilities, like traceability, impact analysis and document generation. Some of the features are illustrated using examples from the Universal Personal Telecommunication (UPT) service.     

轨道交通控制软件中基于场景的需求分析方法

针对轨道交通控制软件的形式化方法,在实际工程应用中存在形式化建模和系统级场景验证困难的问题。提出一种面向轨道交通领域的形式化建模和需求确认及验证方法。通过非形式化、半形式化到形式化规约三步演化过程,为形式化规约构建提供模板。在对需求的确认和验证中,根据形式化规范建立需求模型,导出相关图表,基于此检查领域专家关注的场景。同时制定场景描述规则,使场景可以在需求模型中正确执行。在此基础上,从特殊变量、效率、场景质量三方面对场景进行优化,更充分地验证需求的正确性。实验结果表明,对于典型车载控制软件,该方法较传统分析方法可多探测到10%的潜在缺陷,效率提升80%以上。