One of the most novel features of Casl, the Common Algebraic Specification Language, is the provision of so-called architectural specifications for describing the modular structure of software systems. A brief discussion of refinement of Casl specifications provides the setting for a presentation of the rationale behind architectural specifications. This is followed by some details of the features provided in Casl for architectural specifications, hints concerning their semantics, and simple results justifying their usefulness in the development process.

The way that refinement of individual "local" components of a specification relates to development of a "global" system from a specification of requirements is explored. Observational interpretation of specifications and refinements add expressive power and flexibility while bringing in some subtle problems. The results are instantiated in the context of Casl architectural specifications.

. An object-oriented model of an airport has been developed to assess the parallel object-oriented specification language Maude. The model includes airplanes, gates, baggage handling, ground control and tower and has been implemented on the OBJ3 system, which serves as a rudimentary interpreter for Maude. We discuss two ways of specifying objects and present two notions of behavioral refinement in Maude. 1 Introduction Maude [15, 16, 18] is a language for object-oriented specification. Its semantics is based on concurrent rewriting and can be viewed as a natural extension of the semantics of the OBJ3 rewriting system [9]. Our example is based on a case study at the University of Passau [21], whose goal was the development of a detailed model of an airport in order to gain experience in modeling with Maude and develop techniques for object-oriented specification. As far as possible, the model was implemented and validated in OBJ3. We present a refinement from an abstract to a con...

this paper, we will describe the main techniques for the semantic definition of some of the most used structuring and modular constructs. Our main aim will be to study the generic, "institutionindependent ", version of each construct. However, in order to provide intuition, in most cases, we will first study these constructions in connection to equational logic.

Component based design and development of software is one of the most challenging issues in software engineering. In this paper, we adopt a somewhat simplified view of software components and discuss how they can be conveniently modeled in a framework that provides a modular approach to formal software development by means of stepwise refinements. In particular we take into account an observational interpretation of requirements specifications and study its impact on the definition of the semantics of specifications of (parametrized) components. Our study is carried out in the context of Casl architectural specifications.

The way that refinement of individual “local” components of a specification relates to development of a “global” system from a specification of requirements is explored. Observational interpretation of specifications and refinements add expressive power and flexibility while bringing in some subtle problems. Our study of these issues is carried out in the context of Casl architectural specifications. We introduce a definition of observational equivalence for Casl models, leading to an observational semantics for architectural specifications for which we prove important properties. Overall, this fulfills the long-standing goal of complementing the standard semantics of Casl specifications with an observational view that supports observational refinement of specifications in combination with Casl-style architectural design.

An object-oriented model of an airport has been developed to assess the parallel object-oriented speci#cation language Maude. The model includes airplanes, gates, baggage handling, ground control and tower and has been implemented on the OBJ3 system, which serves as a rudimentary interpreter for Maude. We discuss twoways of specifying objects and present two notions of behavioral re#nement in Maude.

An important problem of the representation of a big dynamic system as a number of interrelating typed ASMs and the subsequent combination of the specifications of individual ASMs into the speci cation of the whole system is investigated in the paper. The structure of such a system is formally defined and a notion of external signature of a typed ASM is introduced. Two main operations for combining existing specifications (and their implementing ASMs) are suggested: import of existing typed ASMs by a new one and union of several typed ASMs into a new one. The syntax and semantics of the operations are formally defined.

We present a logical foundation for object-oriented specifications which supports a rigorous formal development of object-oriented systems. In this setting, we study two different views on a system, the implementor's view (glass-box view) and the user's view (black-box view) which both are founded on a model-theoretic semantics. We also discuss the hierarchical construction of specifications and realisations. Our approach is abstract in the sense that it can be instantiated by various concrete specification formalisms like OCL or JML.

Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 4.5.4 Special Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 4.6 Semantics of Programming Languages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 4.6.1 Semantics of Ada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 4.6.2 Action Semantics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 4.7 Specification Languages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 4.7.1 Early Algebraic Specification Languages . . . . . . . . . . . . . . . . . . . . . . . . 53 4.7.2 Recent Algebraic Specification Languages . . . . . . . . . . . . . . . . . . . . . . . 55 4.7.3 The Common Framework Initiative. . . . . . . . . . . . . . . . . . . . . . . . . . . 56 5 Methodology 57 5.1 Development Phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 5.1.1 Applica...