Adding Multimedia to the Semantic Web: Building an MPEG-7 ontology

For the past two years the Moving Pictures Expert Group (MPEG), a working group of ISO/IEC, have been developing MPEG-7 [1], the "Multimedia Content Description Interface", a standard for describing multimedia content. The goal of this standard is to develop a rich set of standardized tools to enable both humans and machines to generate and understand audiovisual descriptions which can be used to enable fast efficient retrieval from digital archives (pull applications) as well as filtering of streamed audiovisual broadcasts on the Internet (push applications). MPEG-7 is intended to describe audiovisual information regardless of storage, coding, display, transmission, medium, or technology. It will address a wide variety of media types including: still pictures, graphics, 3D models, audio, speech, video, and combinations of these (e.g., multimedia presentations). MPEG-7 is due for completion in October 2001. At this stage MPEG-7 definitions (description schemes and descriptors) are expressed solely in XML Schema [2-4]. XML Schema has been ideal for expressing the syntax, structural, cardinality and datatyping constraints required by MPEG-7. However it has become increasingly clear that in order to make MPEG-7 accessible, re-usable and interoperable with other domains then the semantics of the MPEG-7 metadata terms also need to be expressed in an ontology using a machine-understandable language. This paper describes the trials and tribulations of building such an ontology represented in RDF Schema [5] and demonstrates how this ontology can be exploited and reused by other communities on the semantic web (such as TV-Anytime [6], MPEG-21 [7], NewsML [8], museum, educational and geospatial domains) to enable the inclusion and exchange of multimedia content through a common understanding of the associated MPEG-7 multimedia content descriptions.