Relationships between and among models
ACM SIGART Bulletin · 1980
Mylopoulos : When we talk about a model, it can be either a program snapshot or execution, or a program, a data base, a conceptual schema, or a knowledge base. We can think of a program as consisting of units of some sort, e.g., procedures, assertions, data types; and they are related by relationships of various kinds. Some relationships are user-defined and dependent on the domain the model is dealing with. On the other hand, some of the relationships used to describe the model are primitive, in the sense that their semantics are well-defined and embedded in the modelling framework in terms of which the model has been defined. Some examples from the three areas being represented here are ISA, PART-OF, INSTANCE-OF. Certain other relationships include procedural attachment, used in AI to associate procedures to data classes to specify operations on instances of the classes. In programming languages, considering statements as the units, statement sequencing is a primitive relationship between these units. Considering ALGOL-like begin blocks as the units, scoping rules are relationships between units (blocks). Procedure activation rules between blocks are another example of a relationship that can be considered as primitive and embedded in the modelling framework. Simula concatenation, which allows the definition of classes to be given in terms of other classes gives a relationship between classes. The association of operations to a data type can also be treated as a relationship that has been used in PLs.