Horst Hansen

The ACT-system: experiences and future enhancements

The ACT-system, which comprises an implementation of the algebraic specification language ACT ONE, an Interpreter, a Persistency Checker and a Pretty-Printer, is a specification environment, which is used for the development of specifications for software systems. Here we focus on the environment of the Interpreter, which includes implementations for the concept of object-variables with assignment and the concept of input and output conversion. The former concept is analogous to variables and assignment as known from programming languages while the latter is equivalent to the concept of input- and output-formats of high-level programming languages. It will be shown that this environment greatly enhances the usability of the Interpreter in the ACT-system. Furthermore a new interpretation technique is proposed, which works with arbitrary algebraic specifications. These concepts together allow testing of all algebraic specifications with initial or free functor semantics as well as using them as prototypes of software systems in a convenient way.

Categories for the development of algebraic module specifications

The theory of algebraic module specifications with horizontal structuring operations, like composition, actualization and union, is extended by vertical development steps, like refinement, simulation and transformation, and a realization concept of interface by module specifications. Various compatibility results between horizontal operations, vertical steps and realization are explicitly presented and summarized as one compatibility result in a basic development category. Five independent modifications, which are important for practical specification development, are sketched in the paper leading to several other development categories where corresponding compatibility results are true under some additional side conditions.

Towards Abstract User Interfaces for Formal System Specifications

In this paper we propose the concept of an abstract user interface which is an abstract version of some important parts of a user interface as known in software engineering. The main advantage of an abstract user interface formulated in BNF-terms compared with an ordinary user interface written in natural language is the possibility to translate the abstract user interface into a formal specification of the corresponding system. This is achieved by translating the formal parts of an abstract user interface into separate texts of the same formal specification language which is also used for the executable system specification. We link these parts by a third specification text in the same language, which gives an interpretation of the user command language in terms of the system specification. So the resulting executable specification is a prototype of the software system, eguipped with an abstract user interface. We exhibit this method by an example, a simple screen-oriented editor.

Algebraic Software Development Concepts for Module and Configuration Families

Configuration families are the means of keeping track of structural and historical relationships between the components of a system as they evolve over time. Thus they form a kernel of a configuration management system. In this paper, we study configuration families within a formal semantic framework for modules and their interconnection operations. Our goal is to formulate and prove formally fundamental ideas in this area to serve as a guide to the design of methodologies and tools for software engineering.

Compatibility problems in the development of algebraic module specifications

Abstract Algebraic theory provides a framework for the specification and design of modules and modular software systems. Research in this area has focused on the development of “horizontal” operations for building up module and interface specifications. Our previous work also introduced the notion of vertical development steps, where abstract specifications are converted into a more concrete form. In this paper, we study a variety of compatibility problems between structuring operations and development steps and introduce notions of the realization of an interface specification by a module specification. These compatibility problems are studied in a categorical framework where specifications and developments steps are viewed as objects and morphisms in a “development category”. We show that compatibility can be expressed as the fact that the structuring operations can be extended to partial functors and give sufficient conditions for this property.

Modular Algebraic Specifications

Module, import, export and detail hiding are well-known notions in software engineering. If algebraic specifications together with their operational semantics of term rewriting should be useful as a programming language, similar concepts must be developed to cope with very large specifications. Especially the concept of detail hiding is important, since many problems and their efficient solutions require hidden sorts or hidden functions.