The introduction of user-assisting features into database systems is discussed along two stages. The first stage involves a basic facility that can be used with standard database systems, whereas in the second stage such features are expanded in order to cope with object-oriented systems, adopting semantically richer data models. Examples involving categorization and role-specialization semantic hierarchies illustrate the discussion. A class/metaclass architecture, such as that of the VODAK database system, an algebraic view of query processing and an extension of the object-oriented data model by rule systems are shown to be particularly suitable to design and implement user assistance on the database schema level.

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