Specification of Invariability in OCL

Abstract

Abstract. The paradigm of contractual specification provides a transparent way of specifying systems. It clearly distinguishes between client and implementer obligations. One of the best known languages used for this purpose is OCL. Nevertheless, OCL does not provide primitives for a compact specification of what remains unchanged when a method is executed. In this paper, problems with specifying invariability are listed and some weaknesses of existing solutions are pointed out. The question of specifying invariability in OCL is studied and a simple but expressive and flexible extension is proposed. It is shown that this extension has a simple OCL based semantics.

Specification of invariability in OCL

“…In this subsection, we define the notion of view in terms of the UML 2 metamodel [42] as opposed to the notion of view defined in [30] which was based on UML 1.5 [41]. We show how to define views corresponding to packages and discuss the relation between notions defined so far and the UML 2 metamodel.…”

“…In this section, we redefine the syntax of the OCL extension proposed in [30]. The difference is that we use the string only as a keyword indicating that the predefined feature allInstances is taken into consideration.…”

“…In the paper [30], we proposed an extension of OCL for a compact and precise invariability specification. The idea is to use pairs consisting of a set of objects defined by an arbitrary OCL term and of a modifiable attribute.…”

“…It is a new concept, not just a simple extension of modifiable JML clause. This paper is a journal version of [30]. The main contribution of this paper is a new and more detailed semantics of invariability clauses and its investigation in the context of the notion of reduct as it is used in order-sorted algebras and database theory.…”

“…Invariability specification in OCL should also not force the specifier to disclose internal system details. In the paper [30], we proposed a notion of view based on UML 1.5 [41]. In the meantime, the standard has been upgraded.…”