Querying multimedia presentations based on content

In this paper, we consider the problem of querying multimedia presentations based on content information. We believe that presentations should become an integral part of multimedia database systems and users should be able to store, query, and, possibly, manipulate multimedia presentations using a s ingle database management system software. Multimedia presentations are mod eled as presentation graphs, which are directed acyclic graphs that visuall y specify multimedia presentations. Each node of a presentation graph repre sents a media stream. Edges depict sequential or concurrent playout of stre ams during the presentation. Information captured in each individual stream and the presentation order of streams constitute the content information o f the presentation. Querying multimedia presentation graphs based on conten t is important for the retrieval of information from a database. We present a graph data model for the specification of multimedia presentations and d iscuss query languages as effective tools to query and manipulate multimedi a presentation graphs with respect to content information. To query the inf ormation flow throughout a multimedia presentation, as well as in each indi vidual multimedia stream, we use revised versions of temporal operators Nex t, Connected, and Until, together with path formulas. These constructs allo w us to specify and query paths along a presentation graph. We present an i con-based, graphical query language, GVISUAL, that provides iconic represen tations for these constructs and a user-friendly graphical interface for qu ery specification. We also present an OQL-like language, GOQL (Graph OQL), with similar constructs, that allows textual and more traditional specifica tions of graph queries. Finally, we introduce GCalculus (Graph Calculus), a calculus-based language that establishes the formal grounds for the use of temporal operators in path formulas and for querying presentation graphs w ith respect to content information. We also discuss GCalculus/S (GCalculus with sets) which avoids highly complex query expressions by eliminating uni versal path quantifier, the negation operator, and the universal quantifier . GCalculus/S represents the formal basis for GVISUAL, i.e., GVISUAL uses t he constructs of GCalculus/S directly.