Materialized Object-Oriented Views in MultiView

Object-oriented view mechanisms have received much attention in the literature in recent years, since they provide powerful mechanisms for addressing tasks such as customized tool interfacing to object-oriented databases (OODBs) and interoperability of heterogeneous databases. However, little progress has been made thus far on addressing the topic of view materi-alization in object-oriented databases. In the context of the MultiView project, we have developed an object model and an accompanying set of algorithms for the support of updatable materialized views in OODBs. We take advantage of unique features of the Multi-View model, including its support for object-preserving queries, the integration of base and virtual classes into a uniied and consistent global class hierarchy, and an object-slicing approach. In this paper, we present the MultiView model of materialized views, supporting updates on both base and virtual classes. We also describe a set of eecient algorithms for incremental view maintenance. View technology has been recognized as an important technique for integrating heterogeneous and distributed systems, and for achieving interoperability by hiding idiosyncrasies of component systems to be integrated into one uniied, yet federated system. View materialization, i.e., the maintenance of derived data instead of recomputing it on demand, has been demonstrated in the relational model to improve query access times 7]. Possible applications of materialized view technology include providing selective replication for partitioned or centralized distributed systems, and aiding with the integration of federated DBMSs by providing replication transparency. A number of researchers have proposed view systems for object-oriented databases (OODBs) 1, 9, 14, 21, 18, 19], but little work has been done thus far on the support of materialized object-oriented views. Here at the University of Michigan, we have an ongoing NSF-funded project called MultiView, which has the goal of developing techniques as well as tools for the support of updatable object-oriented views 18, 14, 19, 20]. In the course of our research we have identiied certain fundamental DBMS features as necessary for the support of views. These features include multiple classiication (to allow an object to be an instance of multiple classes) and dynamic reclassiication (to let an object gain and lose class membership of virtual classes dynamically). The object representation assumptions underlying most OODB systems|namely one most-speciic type per object, object layout determined at object-creation time, xed typing and upwards inheritance|connict with these identiied requirements. In order to support the required features, we have developed a novel modeling approach based …