SDM is a high-level semantics-based database description and structuring formalism (database model) for databases. This database model is designed to capture more of the meaning of an application environment than is possible with contemporary database models. An SDM specification describes a database in terms of the kinds of entities that exist in the application environment, the classifications and groupings of those entities, and the structural interconnections among them. SDM provides a collection of high-level modeling primitives to capture the semantics of an application environment. By accommodating derived information in a database structural specification, SDM allows the same information to be viewed in several ways; this makes it possible to directly accommodate the variety of needs and processing requirements typically present in database applications. The design of the present SDM is based on our experience in using a preliminary version of it. SDM is designed to enhance the effectiveness and usability of database systems. An SDM database description can serve as a formal specification and documentation tool for a database; it can provide a basis for supporting a variety of powerful user interface facilities, it can serve as a conceptual database model in the database design process; and, it can be used as the database model for a new kind of database management system.

An approach to the coordinated sharing and interchange of computerized information is described emphasizing partial, controlled sharing among autonomous databases. Office information systems provide a particularly appropriate context for this type of information sharing and exchange. A federated database architecture is described in which a collection of independent database systems are united into a loosely coupled federation in order to share and exchange information. A federation consists of components (of which there may be any number) and a single federal dictionary. The components represent individual users, applications, workstations, or other components in an office information system. The federal dictionary is a specialized component that maintains the topology of the federation and oversees the entry of new components. Each component in the federation controls its interactions with other components by means of an export schema and an import schema. The export schema specifies the information that a component will share with other components, while the import schema specifies the nonlocal information that a component wishes to manipulate. The federated architecture provides mechanisms for sharing data, for sharing transactions (via message types) for combining information from several components, and for coordinating activities among autonomous components (via negotiation). A prototype implementation of the federated database mechanism is currently operational on an experimental basis.

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One important step in integrating heteroge-neous databases is matching equivalent at-tributes: Determining which fields in two databases refer to the same data. The mean-ing of information may be embodied within a. database model, a conceptual schema, appli-cation programs, or data contents. Integra-tion involves extracting semantics, expressing them as metadata, and matching semantically equivalent data elements. We present a proce-dure using a classifier to categorize attributes according to their field specifications and data values, then train a neural network to recog-nize similar attributes. In our technique, the knowledge of how to match equivalent data elements is “discovered ” from metadata, not “pre-programmed”. 1

The role-set approach is a new conceptual framework for data integration in multidatabase systems that maintains the materialization autonomy of local database systems and provides users with more accurate information. The role-set approach presents the answer to a query as a set of relations where the distinct intersections between the relations corresponding to the various roles played by an entity.