Due to global trends, like the rise of the Internet, the cheapness of storage space and the ease of digital media acquisition, vast collections of digital media, are becoming ubiquitous. Futuristic usage scenarios, like ambient technologies, strive to open up these collections for the consumer market. However, this requires high-level semantic knowledge of the items in the collections. Experiences in the development and usage of multimedia retrieval systems have shown that within a specific, but still limited domain, semantic knowledge can be automatically extracted and exploited. However, when the domain is unspecified and unrestricted, that is, the collection becomes a warehouse, semantic knowledge quickly boils down to generics. The research on Digital Media Warehouses (dmws) focuses on improving this situation by providing additional support for annotation extraction and maintenance to build semantically rich knowledge bases. The following sections will introduce these dmw topics for closely related topics like multimedia storage, the usage/indexing of the extracted annotations for multimedia retrieval, and so forth, the reader is directed to the wide variety of literature on multimedia databases (for example, Subrahmaniam, 1997).