RAISE in Perspective

The RAISE [6] Specification Language, RSL, originated as a development from VDM [9] during a five year effort involving several researchers. The purpose was to improve VDM by augmenting it with a module system, a process description language, a formal semantics standard, and tool support. A goal was to keep the language a wide spectrum language including high level specification constructs as well as low level programming constructs, allowing specification and program fragments to be mixed arbitrarily with each other without imposing a linguistically layered language. The effort resulted in a language inspired by, but in many ways different from VDM. A main deviation from VDM is the emphasis on an algebraic specification-style logic where a module consists of a signature and a set of axioms over the names introduced in the signature. Derived forms exist which reflect the classical VDM definitional style. Correspondingly, types can be abstract sorts as in algebraic specifications or they can be defined through type definitions as in VDM using what is normally referred to as a model oriented style. The pure model oriented style usually uses such explicit type definitions and a definitional style for functions. The pure algebraic style uses sorts and more liberal equations with arbitrary terms on the left hand side as well as on the right hand side. In the axiomatic style emphasis is on operations and how they relate to each other. In the model oriented style there is a specific emphasis on type equations. When modeling a problem in VDM, the problem is usually first approached by writing down a set of type definitions using set, list and map type constructors. Operations are subsequently defined referring to the operators allowed on values of these types. The same style is possible in RSL, although the added module system suggests the association