A formal specification for a hierarchy of collections

This paper presents a formal specification for a hierarchy of types similar to the Collection hierarchy presented by the Smalltalk language. The specification method is an extension of VDM supporting the inheritance of specifications, with the property that subtypes are `behaviour-compatible´ with their parents. This formalism gives us a clear concept of behaviour compatibility, and is used to justify the hierarchy structure and to compare the inheritance of specifications, adopted, with the inheritance of implementations, adopted in Smalltalk