The Moving Picture Experts Group

Query Format

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The increased availability and usage of digital images has highlighted the need for efficient multimedia data storage and retrieval solutions. Currently, there are numerous storage and retrieval approaches ranging from commercial products to the purely academic. The diversity of these individual projects prevents users from experiencing broad and unified access to different multimedia collections. In fact, almost every solution provides a different retrieval interface and is based on different multimedia metadata description formats. The varied query approaches along with the alternate metadata description formats and retrieval interfaces prevents effective interoperability among current multimedia retrieval systems. In this context, ISO/IEC JTC1/SC29 WG11 (more commonly known as MPEG) established the MPEG Query Format (MPQF) [1, 2, 3, 4, 5, and 6] standardization to create a standard interface for media repositories. The MPEG Query Format, also known as MPQF, facilitates a standard multimedia query language so that service providers can offer users and applications a unified interface for querying media repositories.

The general goal of MPQF is to provide a standard multimedia query language to unify access to distributed multimedia retrieval systems. To achieve this goal, the MPQF standard specifies precise input and output parameters to express multimedia requests and to allow clients easy interpretation and processing of result sets. Moreover, the management component of the MPQF covers searching and the choice of the desired multimedia services for retrieval. For this purpose, the standard provides a means to describe service capabilities and to undertake service discovery. It is also important to note that while the MPQF is part 12 of the MPEG-7 standard, the specification explicitly allows for deployments using any XML-based multimedia metadata description format.

One of the key features of MPQF is that it allows the expression of multimedia queries combining both the expressive style of information and XML Data Retrieval systems. Thus, MPQF combines e.g. keywords and query-by-example with e.g. XQuery allowing the fulfillment of a broad range of users' multimedia information requirements. Both approaches to data retrieval aim to facilitate clients' access to information, but from different points-of-view. On one hand, given a query expressed in a user-oriented manner (e.g. an image of a bird with blue wing tips), an Information Retrieval system aims to retrieve information that might be relevant even though the query is not formalized. In contrast, a Data Retrieval system (e.g. an XQuery-based database) deals with a well-defined data model and aims to determine which objects of the collection satisfy clearly defined conditions in a relational algebra expression (e.g. the title of a movie, the size of a video file or the fundamental frequency of an audio signal). For a data retrieval system, like a relational database or an XML repository, a single erroneous object among thousands retrieved means a total failure. In contrast, an information retrieval system can supply results that appear relevant and expect a user to 'filter' those results further.

With regard to the task of Information Retrieval, MPQF offers a broad range of possibilities that include but are not limited to query-by-example-media, query-by-example-description, query-by-keywords, query-by-feature-range, query-by-spatial-relationships, query-by-temporal-relationships and query-by-relevance-feedback. For Data Retrieval, MPQF offers its own XML query algebra for expressing conditions over the multimedia related XML metadata (e.g. MPEG-7, Dublin Core or any other XML-based metadata format) but also offers the possibility to embed XQuery expressions.

In 2012, MPEG released a second edition of MPQF (ISO/IEC 15938-12:2012) that cancels and replaces the first one (ISO/IEC 15938-12:2008), which has been technically revised. The second edition also incorporates all the previous amendments and corrigenda, i.e. ISO/IEC 15938-12:2008/Cor.1:2009, ISO/IEC 15938-12:2008/Cor.2:2010, ISO/IEC 15938-12:2008:Amd.1:2011 and ISO/IEC 15938-12:2008:Amd.2:2011.