Issues in processing similarity queries for multimedia databases

The extension of data types in multimedia databases has resulted in an important change of the content query paradigm which significantly differs from that of traditional database systems and thus requires new approaches to the query evaluation. The most important difference is that a response to a query typically provides not only a set of objects, but also the grades with which these objects qualify. In this article, recent developments in this area are summarized and pointers to relevant original articles are provided. Open problems are also discussed and future research directions proposed.