Axioms of Versioning
Marc de Graauw
The problems of language versioning can be better understood with the help of some formal axioms defining the relations among the extensions and semantics of languages. Such axioms allow us to specify what makes one language extensionally, syntactically, or semantically a subset, superset, or equivalent of another. The difference between syntactic and semantic compatibility makes clear how languages can grow in a forward-compatible way. The key to compatible versioning is to assign new semantics in the new version of a language for syntax that was already accepted in the prior version, but to which the prior version assigned no semantics.