The comprehensiveness results from the fact that the standard has been designed for a broad range of applications and thus employs very general and widely applicable concepts. The standard contains a large set of tools for diverse types of annotations on different semantic levels (the set of MPEG-7 XML Schemas define 1182 elements, 417 attributes and 377 complex types). The flexibility is very much based on the structuring tools and allows the description to be modular and on different levels of abstraction. MPEG-7 supports fine grained description, and it provides the possibility to attach descriptors to arbitrary segments on any level of detail of the description. The possibility to extend MPEG-7 according to the conformance guidelines defined in part 7 provides further flexibility.
Two main problems arise in the practical use of MPEG 7 from its flexibility and comprehensiveness: complexity and limited interoperability. The complexity is a result of the use of generic concepts, which allow deep hierarchical structures, the high number of different descriptors and description schemes and their flexible inner structure, i.e. the variability concerning types of descriptors and their cardinalities. This causes sometimes hesitance in using the standard. The interoperability problem is a result of the ambiguities that exist because of the flexible definition of many elements in the standard (e.g. the generic structuring tools). There can be several options to structure and organize descriptions which are similar or even identical in terms of content, and they result in conformant, yet incompatible descriptions. The description tools are defined using DDL. Their semantics is descibed textually in the standard documents. Due to the wide application are, the semantics of the description tools are often very general. Several works have already pointed out the lack of formal semantics of the standard that could extend the traditional text descriptions into machine understandable ones. These attempts that aim to bridge the gap between the multimedia community and the Semantic Web, either for the whole standard, or just one of its part, are detailed below.