Enhancing the semantic interoperability of multimedia through a core ontology

A core ontology is one of the key building blocks necessary to enable the scalable assimilation of information from diverse multimedia sources. A complete and extensible ontology that expresses the basic concepts that are common across a variety of domains and media types and that can provide the basis for specialization into domain-specific concepts and vocabularies, is essential for well-defined mappings between domain-specific knowledge representations (i.e., metadata vocabularies) and the subsequent building of a variety of services such as cross-domain searching, tracking, browsing, data mining and knowledge acquisition. As more and more communities develop metadata application profiles which combine terms from multiple vocabularies (e.g., Dublin Core, MPEG-7, MPEG-21, CIDOC/CRM, FGDC, IMS), a core ontology will provide a common understanding of the basic entities and relationships, which is essential for semantic interoperability and the development of additional services based on deductive inferencing. In this paper, we first propose such a core ontology (the ABC model) which was developed in response to a need to integrate information from multiple genres of multimedia content within digital libraries and archives. Although the MPEG-21 RDD was influenced by the ABC model and is based on a model extremely similar to ABC, we believe that it is important to define a separate and domain-independent top-level extensible ontology for scenarios in which either MPEG-21 is irrelevant or to enable the attachment of ontologies from communities external to MPEG, for example, the museum domain (CIDOC/CRM) or the biomedical domain (ON9.3). We evaluate the ABC model's ability to mediate and integrate between multimedia metadata vocabularies by illustrating how it can provide the foundation to facilitate semantic interoperability between MPEG-7, MPEG-21 and other domain-specific metadata vocabularies. By expressing the semantics of both MPEG-7 and MPEG-21 metadata terms in RDF Schema/DAML+OIL [and eventually the Web Ontology Language (OWL)] and attaching the MPEG-7 and MPEG-21 class and property hierarchies to the appropriate top-level classes and properties of the ABC model, we have defined a single distributed machine-understandable ontology. The resulting ontology provides semantic knowledge which is nonexistent within declarative XML schemas or XML-encoded metadata descriptions. Finally, in order to illustrate how such an ontology will contribute to the interoperability of data and services across the entire multimedia content delivery chain, we describe a number of valuable services which have been developed or could potentially be developed using the resulting merged ontologies.