function. The set of
entity types linked by a relation type is called its signature. Type
languages are related through type language morphisms. A type language
morphism from source type language to target type language maps source
entity (relation) types to target entity (relation) types, preserving
reference, signature and arity. The context of languages <span
 style="font-family: arial; font-weight: bold;">Language</span>
consists of
first order type languages and their morphisms. The context <span
 styl