Contrary to other approaches, which are based on schema integration, it is not necessary to construct a global schema. Instead, database schemas and their data models are kept separate, and a multidatabase query language based on relational algebra is proposed. Semantically equivalent data elements are identified interactively by the system and the user in a joint effort. The system preserves the autonomy of the individual databases, which also means that different database descriptions and data models are allowed to coexist. A data catalog is used to store descriptions of the different data models, data types, query languages, and database schemas, as well as procedures for parsing data definitions, transforming query languages, and so on.
Users start by selecting the databases and importing their data definitions.
Then they can navigate through these definitions much as they would browse a hypertext system. The query is constructed by selecting icons and is represented graphically as a connected graph. Finally, such a multidatabase query is not translated, but decomposed into subqueries with operators supported by the individual database management systems. The query used in the example is a simple one, where parts matching invoice 123xyz must be retrieved. It is not immediately clear whether it is possible to formulate more complex queries, or what must happen when data elements are redundantly stored in the IMS database.