Profiles and levels have been proposed as a means to reduce the complexity of MPEG-7 descriptions (ISO, 2005). Like in other MPEG standards, profiles are subsets of the standard that cover certain functionalities, while levels are flavours of profiles with different complexity. In MPEG-7, profiles are subsets of description tools for certain application areas, levels have not yet been used. The proposed process of the definition of a profile consists of three steps:
- Selection of tools supported in the profile, i.e. the subset of descriptors and description schemes that are used in description that conform to the profile.
- Definition of constraints on these tools, such as restrictions on the cardinality of elements and on the use of attributes.
- Definition of constraints on the semantics of the tools, which describe their use in the profile more precisely.
The result of tool selection and the definition of tool constraints are formalized using the MPEG-7 DDL and result in an XML schema like the full standard.
Several profiles have been under consideration for standardization and three profiles have been standardized (they constitute part 9 of the standard, with their XML schemas being defined in part 11):
Simple Metadata Profile (SMP)
Allows describing single instances of multimedia content or simple collections. The profile contains tools for global metadata in textual form only. The proposed Simple Bibliographic Profile is a subset of SMP. Mappings from ID3, 3GPP and EXIF to SMP have been defined.
User Description Profile (UDP)
Its functionality consists of tools for describing user preferences and usage history for the personalization of multimedia content delivery.
Core Description Profile (CDP)
Allows describing image, audio, video and audiovisual content as well as collections of multimedia content. Tools for the description of relationships between content, media information, creation information, usage information and semantic information are included. The profile does not include the visual and audio description tools defined in parts 3 and 4.
The adopted profiles will not be sufficient for a number of applications. If an application requires additional description tools, a new profile must be specified. It will thus be necessary to define further profiles for specific application areas. For interoperability it is crucial, that the definitions of these profiles are published, to check conformance to a certain profile and define mappings between the profiles. It has to be noted, that all of the adopted profiles just define the subset of description tools to be included and some tool constraints; none of the profile definitions includes constraints on the semantics of the tools that clarify how they are to be used in the profile.
Apart from the standardized ones, a profile for the detailed description of single audiovisual content entities called Detailed Audiovisual Profile (DAVP) has been proposed. The profile includes many of the MDS tools, such as a wide range of structuring tools, as well as tools for the description of media, creation and production information and textual and semantic annotation, and for summarization. In contrast to the adopted profiles, DAVP includes the tools for audio and visual feature description, which was one motivation for the definition of the profile. The other motivation was to define a profile the supports interoperability between systems using MPEG-7 by avoiding possible ambiguities and clarifying the use of the description tools in the profile. The DAVP definition thus includes a set of semantic constraints, which play a crucial role in the profile definition. Due to the lack of formal semantics in DDL, these constraints are only described in textual form in the profile definition (Bailer et.al., 2006: The Detailed Audiovisual Profile: Enabling Interoperability between MPEG-7 Based Systems W. Bailer and P. Schallauer. In Proc. of 12th International Multi-Media Modeling Conference, Beijing, CN, 2006)