Inheritance and subtyping [object-oriented databases]

A method for implementing subtyping and inheritance, as independent features of object-oriented languages, is presented. There are at least two reasons for decoupling subtyping from inheritance: the negative influence on encapsulation and the different perspective of specification inheritance (subtyping) and implementation inheritance (code sharing). Subtyping and inheritance are defined in two independent constructs: the class module and the implementation module which are separately compiled. Subtyping is declared in the class module which contains all the public definitions of the class (e.g., types ad operation signatures), while inheritance is defined in the implementation module, which contains the implementations of all the operations of the class. The class module includes assertions which are an algorithmic form of operation specification