Digital Libraries (DLs) are repositories for large collection of digitized data. Traditionally, these libraries have been used to manage structured text documents with embedded images. In future, these libraries will have to handle multimedia data types as well, such as video, audio, images, graphics, and animations etc. Multimedia digital libraries (MMDLs) will emerge as a standard for information management. They will store structured media information in the form of multimedia documents (MMDs). One major problem in implementing these libraries is data integration, since different multimedia data types use different data models and structures to represent and store the information. We use (a) XML Schema and MPEG-7 content description standards for structural and content-basedmodeling of MMDs and (b) the object-relational (OR) data model as a unified approach for representation, storage, and retrieval of structured MMDs. The OR model makes it possible to pose semantic as well as content-based queries to the MMDLs thus enabling access and retrieval of any type of information contained in the constituent MMDs.