Integrating View Schemata Using an Extended Object Definition Language

Abstract

View mechanisms play an important role in restructuring data for users, while maintaining the integrity and autonomy for the underlying database schema. Although far more complex than their relational counterparts, numerous object-oriented view mechanisms have been specified and implemented over the last decade. These view mechanisms have served different functions: view schemata for object-oriented databases; object views of relational (and other) database systems, and the formation of federated schemata for distributed information systems. In the latter category there is still a significant amount of research required to construct a view language powerful enough to support federated views. Such a language (or set of languages) should support not only object views, but also a wrapper specification language for external information sources, and a set of restructuring and integration operators. Furthermore, with the advent of standard models and technologies such as CORBA for distribution, ODMG for storage, and XML for web publishing, these languages should be based upon, or cooperate with, these standards. In this research, we present a view mechanism which retains the semantic information incorporated in ODMG schemata, provide a set of operators which facilitate the restructuring and integration necessary to merge schemata, and provide wrappers to heterogenous systems such as legacy systems, ODBC databases, and XML data sources.

A metadata approach to multimedia database federations

“…View support in this metamodel is designed to represent the view mechanism specified in Ref. [20]. Each object view, represented as an instance of sys_SubSchema metaclass, contains one or more virtual classes.…”

“…Virtual class is recursively constructed from base classes or other virtual classes using restructuring operators specified in Ref. [20].…”

“…For further information on the object view model used in the EGTV multimedia federation please refer to Ref. [20]. † Federated Layer.…”

“…The EGTV sys_Class defines additional attributes virtualLevel, operatorType and relationship virtualConnector for representing virtual classes. These attributes are mapped only to the ODMG extensions for object views [20].…”

Flattening the Metamodel for Object Databases

“…If views are to be defined for complex ODMG schemas, and these views (and their virtual classes) are to be reused by other views, the storage of a string representation (of a view definition) is not sufficient. An extension to the ODMG metamodel which facilitated the representation of virtual subschemas was presented in [15]. The extension of our metamodel to incorporate views will be treated in a separate paper.…”