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This paper describes an approach to module composition by executing "module expressions" to build systems out of component modules; the paper also gives a novel semantics intended to aid implementers. The semantics is based on set theoretic notions of tuple set, partial signature, and institution, thus avoiding more difficult mathematics theory. Language features include information hiding, both vertical and horizontal composition, and views for binding modules to interfaces. Vertical composition refers to the hierarchical structuring of a system into layers, while horizontal composition refers to the structure of a given layer. Modules may involve information hiding, and views may involve behavioral satisfaction of a theory by a module. Several "Laws of Software Composition" are given, which show how the various module composition operations relate. Taken together, this gives foundations for an algebraic approach to software engineering. 1.1 Introduction The approach to module compos...

An overview of past, present and future work on the Extended ML formal program development framework is given, with emphasis on two topics of current active research: the semantics of the Extended ML specification language, and tools to support formal program development.

This paper will be most easily appreciated by the reader with some prior knowledge of Mathematical Logic [8, 19], Set Theory [11], and Denotational Semantics [9, 18, 20]. Verdi differs from its predecessor m-Verdi [4] in several significant ways:

When a system is extended by adding undo, the original system behaviour should be preserved within the new extended system. In this paper a formal framework is established which considers the state of the system before and after the extension and captures the relationship between the layers in a structure we call conservative encapsulation or the cube. Alternative algebraic properties of undo and examples of two specific undo policies are formalised within this framework. The framework afforded by conservative encapsulation is not just suitable for undo, but can be used to study other forms of system extension such as history mechanisms.

This document provides a comparative study of the different alternatives for the executable (sequential) specification language which must be selected for the IPTES mini-specifications. This investigation will be focussed on notations from existing model-oriented methods where appropriate subsets can be extracted. However, existing executable languages inspired from such model-oriented methods also form a basis for this investigation. An Investigation of Executable Specification Languages for the IPTES Mini-: : : Contents 1 Introduction 2 2 Background about the VDM history 2 3 An overview of the considered notations 3 3.1 BSI/VDM-SL : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 3 3.2 VIP VDM SL : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 4 3.3 RAISE SL : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 5 3.4 Me too : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 6 3.5 EPROL : : : : : : : : : : : : : : : : : : : : : : : : : : ...