Using Fagin's algorithm for merging ranked results in multimedia middleware

A distributed multimedia information system allows users to access data of different modalities, from different data sources, ranked by various combinations of criteria. Fagin (1996) gives an algorithm for efficiently merging multiple ordered streams of ranked results, to form a new stream ordered by a combination of those ranks. In this paper we describe the implementation of Fagin's algorithm in an actual multimedia middleware system, including a novel, incremental version of the algorithm that supports dynamic exploration of data. We show that the algorithm would perform well as part of a single multimedia server and can even be effective in the distributed environment (for a limited set of queries), but that the assumptions it makes about random access limit its applicability dramatically. Our experience provides a better understanding of an important algorithm, and exposes an open problem for distributed multimedia information systems.