Quorum-Based Replication of Multimedia Objects in Distributed Systems

In information systems, resource objects like databases are distributed and replicated in order to increase the performance, reliability, and availability. Especially, multimedia objects like movies are distributed. In this paper, we consider multimedia objects which are characterized in terms of not only data structure but also quality of service (QoS). Here, a pair of replicas of a movie object may have the same content but different levels of QoS, e.g. fully coloured and monochromatic ones. Thus, kinds of replicas of a multimedia object are distributed to peers in various ways. Replicas of an object are thus partially ordered in terms of newness of contents and QoS. In traditional quorum theories, it is critical to find which replica is the newest in each quorum. In this sense, replicas are totally ordered in terms of newness. On the other hand, the content may be the newest but the QoS may not be the newest in a replica of a multimedia object. Replicas of an object are thus partially ordered in terms of newness of contents and QoS. We newly define a partially ordering relation, newness-precedency of replicas to show which replica is newer than another in terms of content and QoS. We classify operations on an object to types with respect to whether or not a transaction inputs and outputs data in an object. We define a quorum for each operation type of an operation on the basis of the newness-precedent relation. We discuss how to synchronize multiple replicas to make consistent on the basis of the quorum concept.