Nico Plat

An overview of the ISO/VDM-SL standard

VDM-SL, the notation incorporated in the formal method VDM, is currently being standardized under auspices of the International Standards Institution (ISO) and the British Standards Institution (BSI). It is one of the few formal languages of which the syntax and the semantics have been completely formally defined. In this paper we present an overview of the standard, including a report on the current status of the standardization effort.

A Formal Semantics of Data Flow Diagrams

This paper presents a formal semantics of data flow diagrams as used in Structured Analysis, based on an abstract model for data flow transformations. The semantics consists of a collection of VDM functions, transforming an abstract syntax representation of a data flow diagram into an abstract syntax representation of a VDM specification. Since this transformation is executable, it becomes possible to provide a software analyst/designer with two ‘views’ of the system being modelled: a graphical view in terms of a data flow diagram, and a textual view in terms of a VDM specification. In this paper emphasis is on the motivation for the choices made in the transformation. The main aspects of the transformation itself are described using annotated VDM functions with some examples.

Application and benefits of formal methods in software development

Formal methods for software development receive much attention in research centres, but are rarely used in industry for the development of (large) software systems. One of the reasons is that little is known about the integration of formal methods in the software process, and the exact role of formal methods in the software life-cycle is still unclear. In this paper, a detailed examination is made of the application of, and the benefits resulting from, a generally applicable formal method (VDM) in a standard model for software development (DoD-STD-2167A). Currently, there is no general agreement on how formal methods should be used, but in order to analyse the use of formal methods in the software process, a clear view of such use is essential. Therefore, we show what is meant by ‘using a formal method’. The different activities of DoD-STD-2167A are analysed with regard to their suitability for applying VDM and the benefits that may result from applying VDM for that activity. Based on this analysis, an overall view on the usage of formal methods in the software process is formulated.

A Case for Structured Analysis/Formal Design

Both formal methods and structured methods in software development have disadvantages inherent to the class of methods they belong to. A better method may be composed by taking the best of a formal method and the best of a structured method and constructing one, new method. In this paper two approaches to transforming data flow diagrams, the main system representation resulting from SA, to constructs in VDM are described. Each approach can be used as a basis for a combined SA/VDM method. A comparison is made between the two presented models by analyzing their characteristics. Some conclusions on the usability of the combination of SA and VDM are presented.

Standards for Non-Executable Specification Languages

This paper discusses the impact of the standardisation of (non-executable) specification languages; standardisation can increase the interest in, and acceptance of, a specification language, and it stimulates the development of tool support for such a language. It is argued that a specification language should preferably be formally defined. The ISO/ VDMSL standard (under construction) is used as an illustration. The fact that many specification languages are nonexecutable causes problems in the areas of conformance and compliance. These problems are touched upon.

Type Checking BSI/VDM-SL

In this paper a type system for BSI/VDM-SL is described. General characteristics of this system are presented using a formal notation. The main property of the system is that type checking can be done in a single bottom-up tree walk. The advantages and disadvantages of this approach are discussed. It is described how the type system has been implemented with the use of the attribute grammar evaluating system generator GAG.

Structured analysis—formal design, using stream and object oriented formal specifications

Keyphruses: (i) the role of rigorous software specification and design with the Vienna Development Method within the SA / SD traject of software development, (ii) extension of VDM-SL, (the VDM Specification Language) by means of a object otiozted structuring mechanism, together with stream oriented properties, to enable stream and object oriented specification. Relation to Workshop Topics of Interest: the research addresses a specific role for formal methods in large-scale software development and the (mechanized) support for this role for formal methods in particular.