This paper introduces the key principles and main features of the VODAK Model Language VML. This includes the standard concepts in object-oriented data modelling needed in the subsequent discussion, like objects, classes, types, inheritance and methods. Then the application ofVML for modelling hypermedia documents is discussed. Advanced features in order to tailor data models towards particular application scenarios, that will be needed in order to provide adequate models for hypermedia documents, are introduced. Among these are metaclasses, parametrized object types, semantic relationships and dynamic method delegation. Modelling primitives are designed to model typed hierarchical and hypertext document structures. Particular attention is paid to provide operations that maintain consistency by observing the compositional constraints of document types.

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