Replication and fragmentation of composite objects in distributed database system

New mechanisms are needed to manage the access and manipulation of related data that are distributed over multiple sites in a distributed system. Such distributed related data is modeled by a distributed composite object, where the member objects may reside on different sites. This thesis explores replication and fragmentation techniques to provide efficient access to distributed composite objects stored in database systems. The mechanisms presented here deal with issues of performance, availability, consistency, and autonomy.;In the context of tightly integrated distributed databases systems, distributed composite objects are suitable for modeling multimedia objects, information units of distributed information systems, etc. We present a scheme for supporting such distributed composite objects and address the issues involved in replicating them. A new replication scheme, which allows replication of selected parts (subobjects) of the composite object is proposed. The proposed selective replication scheme can tune the replication granularity to meet both the availability and performance requirements of distributed applications, and at the same time minimize storage costs. An implementation framework for supporting composite object replication that can be adapted to any distributed database system is presented in the context of the O-Raid distributed object-oriented database system. We show the usefulness of composite object replication schemes through an experimental study conducted on O-Raid.;In the context of a collection of autonomous database systems, we propose the use of a distributed composite object with no replication as a means for data distribution. A transaction processing scheme based on object fragmentation is proposed, where the data is fragmented to the local databases. Our approach is based on a dynamic reconfiguration of object fragments at run time so that the locality of access can be re-established. The scheme preserves site autonomy as all data access is handled by local database level. The only global activities required are infrequent negotiation transactions (needed for reconfiguration) and propagation of fragmentation information. We illustrate the key idea through several examples, present a theoretical framework for modeling object fragmentation, discuss dynamic object reconfiguration schemes, and outline the language constructs for specifying fragment distribution.