View Management Issues in Object - Oriented Databases

In database terminology, a view is a query that is stored and given a name by which it can be used in other queries. Views are an established technique for virtually restructuring data, classes, and schemata so as to meet the needs of specific applications or users, for integrating heterogeneous and distributed systems (for example, data warehouse systems), and for achieving interoperability by hiding the idiosyncrasies of component systems to be integrated into one unified, yet federated system. Because the restructuring is virtual, applications can use views to customize shared data objects, even adding new extrinsic properties and behavior without affecting other applications’ perceptions of the data. Through view technology, any database object can behave differently depending on in which view’s context it appears. Typically, the contents of a view are derived using the view’s stored query, in which case each query upon the extent of a view must be translated into a query upon the view’s source classes. View materialization, i.e., the maintenance of derived extents of views (as opposed to recomputing them upon demand), has been demonstrated to improve the performance of queries for relational databases. If a view is materialized, then its contents must be maintained in the face of updates to the view’s sources. Current researchers are examining new areas that can specifically benefit from the flexibility provided by objectoriented views. Barsalou et al. use object-based views to integrate object-oriented and relational databases while preserving update capabilities [2]. Ra and Rundensteiner utilize views to provide transparent schema evolution, preserving existing views through schema change [13]. Because the object-oriented paradigm offers a more powerful model for integration than the relational one, several papers discuss the integration of heterogeneous data repositories via objectoriented views [3, 2, 6]. While researchers have begun to study view mechanisms in the context of object-oriented databases (OODBs) [1, 15, 14], little work has been done regarding the implementation of object-oriented views or object-oriented view materialization. Furthermore, of the few research papers that discuss implementations of OODB view systems, most support only limited functionality at this time [11, 12, 15]. The goal of my research is to address issues related to the implementation of object-oriented views, including the object model requirements of an OODB view system, algorithms and strategies that facilitate the maintenance of materialized views, and support for views defined by “complex” queries (e.g., path queries).