Behavioural theories are a generalization of first-order theories where the equality predicate symbol is interpreted by a behavioural equality of objects (and not by their identity). In this paper we first consider arbitrary behavioural equalities determined by some (partial) congruence relation and we show how to reduce the behavioural theory of any class of algebras to (a subset of) the standard theory of some corresponding class of algebras. This reduction is the basis of a method for proving behavioural theorems whenever an axiomatization of the behavioural equality is provided. Then we focus on the important special case of (partial) observational equalities where two elements are observationally equal if they cannot be distinguished by observable computations over some set of input values. We provide general conditions under which an obvious infinite axiomatization of the observational equality can be replaced by a finitary one and we provide methodological guidelines for finding such...

Observability concepts contribute to a better understanding of software correctness. In order to prove observational properties, the concept of Context Induction has been developed by Hennicker [10]. We propose in this paper to embed Context Induction in the implicit induction framework of [8]. The proof system we obtain applies to conditional specifications. It allows for many rewriting techniques and for the refutation of false observational conjectures. Under reasonable assumptions our method is refutationally complete, i.e. it can refute any conjecture which is not observationally valid. Moreover this proof system is operational: it has been implemented within the Spike prover and interesting computer experiments are reported.

. Behavioural logic is a generalization of first-order logic where the equality predicate is interpreted by a behavioural equality of objects (and not by their identity). We establish simple and general su#cient conditions under which the behavioural validity of some first-order formula with respect to a given first-order specification is equivalent to the standard validity of the same formula in a suitably enriched specification. As a consequence any proof system for first-order logic can be used to prove the behavioural validity of first-order formulas. 1 Introduction Observability plays a prominent role in formal software development, since it provides a suitable basis for defining adequate correctness concepts. For instance, for proving the correctness of a program with respect to a given specification, many examples show that it is essential to abstract from internal implementation details and to rely only on the observable behaviour of the program. A similar situation is the not...

Observability concepts contribute to a better understanding of software correctness. In order to prove observational properties, the powerful concept of Context Induction has been developed by Hennicker [Hen91]. We propose in this paper to embed Context Induction in the implicit induction framework of [BR95]. The proof system we obtain applies to conditional specifications. It allows for many rewriting techniques and for the refutation of false conjectures. Under reasonable assumptions it is refutationally complete. Moreover this proof system is operational: it has been implemented within the Spike prover and interesting computer experiments are reported.

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...