The problem of formally analyzing properties of real-time systems is addressed. A method is proposed that allows specifying system properties in the TRIO language (an extension of temporal logic suitable to deal explicitly with the “time ” variable and to measure it) and modeling the system as a timed Petri net. It is argued that such an approach is more general than analyzing program properties. The proof method is based on an axiomatization of timed Petri nets in terms of TRIO so that their properties can be derived as suitable theorems in much the same spirit as classical Hoare’s method allows proving properties of programs coded in a Pascal-like language. The method is then exemplified through two classical “benchmarks ” of the literature on concurrent and real-time systems, namely an elevator system and the dining philosophers problem. A thorough review of the related literature and a comparison thereof with the new method is also provided. Possible alternative methods, theoretical extensions, and practical applications are briefly discussed.

Traditional denotational semantics assigns radically different meanings to one and the same phrase depending on the rest of the programming language. If the language is purely functional, the denotation of a numeral is a function from environments to integers. But, in a functional language with imperative control operators, a numeral denotes a function from environments and continuations to integers. This paper introduces a new format for denotational language specifications, extended direct semantics, that accommodates orthogonal extensions of a language without changing the denotations of existing phrases. An extended direct semantics always maps a numeral to the same denotation: the injection of the corresponding number into the domain of values. In general, the denotation of a phrase in a functional language is always a projection of the denotation of the same phrase in the semantics of an extended language---no matter what the extension is. Based on extended direct semantics, i...

This paper traces the important steps in the history --up to around 1990-- of research on reasoning about programs. The main focus is on sequential imperative programs but some comments are made on concurrency. Initially, researchers focussed on ways of verifying that a program satisfies its specification (or that two programs were equivalent). Over time it became clear that post facto verification is only practical for small programs and attention turned to verification methods which support the development of programs; for larger programs it is necessary to exploit a notation of compositionality. Coping with concurrent algorithms is much more challenging -- this and other extensions are considered briefly. The main thesis of this paper is that the idea of reasoning about programs has been around since they were first written; the search has been to find tractable methods.

this paper to the legal symbolic types only we obtain the following theorem.

Component-based software development (CBSD) technology uses components as first-class objects and therefore requires a good understanding of the nature of components. Industrial approaches to CBSD based on interoperability standards (such as OMG CORBA) lack of component semantics in their descriptional models. In this paper we present an overview of the SYNTHESIS method emerging the CBSD approach by introduction of semantic information to enrich and complement the industrial modeling facilities. The paper contributes to the development of modeling facilities for CBSD focusing on the interoperable systems design. Proper balance of formal and semi-formal modeling facilities is demonstrated to cope with the CBSD requirements 1 . 1 Introduction Component-based software development (CBSD) has become one of the hottest topics in the area of software engineering. CBSD is a promising solution intended to break up large monolithic software systems into interoperable components and thus to m...

We consider type universes as examples of regular algebras in the area of denotational semantics. The paper concentrates on our method which was used implicitly to prove that the interesting domain equations have solutions in the domain universes underlying MetaSoft, cf. [BBP90], and BSI/VDM, cf. [TW90]. Technically speaking the method allows to prove regularity of a universe. It is demonstrated by means of an example that the method applies even to universes which are essentially regular, i.e., which are neither cpo's, nor the images of the initial regular algebra. 1 Introduction 1.1 The Problem It is a usual practice in the area of programming languages to assign types to the manipulated objects. The typing procedure yields the first, naive, explanation of the notion of type: each type stands for the set of objects that have the type assigned to them. Consequently, one demands that the type forming operators should also be interpreted as operations on sets. It was discovere...

In this survey, we describe the following different aspects of modeling multidimensional point sets (shapes) using real-valued functions of several variables: algebraic system as a formal framework; representation of shapes, operations, and relations using real-valued functions, internal representation of the modeling system; specialized language for function-based modeling, and model extension to point sets with attributes (hypervolumes).

was conducted. Declarations I, the undersigned, declare that this thesis has not been submitted to this or any other university. I declare that all of the material contained in this thesis, unless otherwise stated, is entirely my own work. I declare my consent to the library of Trinity College, Dublin, that I agree that the library may lend or copy this thesis upon request.

The specification and verification of communicating systems has captured increasing interest in the last decades. CCS, a Calculus of Communicating Systems [Milner 89a], was especially designed to help this enterprise; it is widely used in both industry and academia. Most efforts