MREA: A relation-extension algebra for processing UMQL-based multimedia queries

UMQL is powerful general-purpose multimedia query language, which allows users to query multimedia data based on their content information. For its internal processing, a relation-extension algebra called MREA is proposed in this paper. Based on the original relation operators, MREA introduces several new operators, mainly including content selection and spatio-temporal selection that are designed for the structure-feature queries and spatio-temporal queries, respectively. The processing methods for these new operators are then given. The well application results in prototype shows that MREA is an effective query algebra and very suitable for processing UMQL-based multimedia queries.