DefiningImageAccess/Standard/MPEG-21
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| DefiningImageAccess/Standard/MPEG-21 | |
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| Link:=http://www.chiariglione.org/mpeg/technologies/mp21-did/index.htm}} | |
| Status:=ISO Standard}} | |
| JISCProject:=False}} | |
| Focus:=Describing Digital Objects}} | |
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MPEG-21 DID
MPEG-21 is a modular, multi-faceted specification for representing digital objects. It also defines a specific XML-based representation. There are many parts to MPEG-21, including metadata specifications for:
- digital item identification (DII),
- intellectual property management and protection (IPMP),
- rights management, i.e., Rights Expression Language(REL) and Rights Data Dictionary (RDD)
- content adaptation, i.e., the Digital Item Adaptation and many others.
But of particular interest is the Digital Item Description (DID), which is an abstract model and XML representation (DIDL) for describing digital objects consisting of multiple data streams and associated descriptive information. DIDs can also be constructed for physical (non-digital) objects, or combinations of physical and digital objects.
The DID framework is very flexible, and, considered alone, is reasonably simple to use.
Key concepts of DID are:
- Resources - datastreams encoding some digital content. A resource may also be some identifiable non-digital thing - this is very similar to the web notion of a resource.
- Components - wrappers for one or more resources, where multiple resources in a component are considered to be equivalent or interchangeable.
- Items - groupings of items and/or components. Thus, an item can have a complex multipart nested structure.
- Descriptors - convey secondary information about items, components or containers. The use of descriptors is optional (but highly desirable).
- Containers - a secondary grouping mechanism: a container may contain other containers and/or items (but note that an item may not contain containers). The use of containers is optional (but may be very usefulk when dealing with complex digital objects).
In the XML representation (DIDL) of a DID:
- a resource is represented by a
<didl:Resource>element, and may contain the resource inline or use a URI to refer to an externally held datastream. A MIME content-type expression is associated with the datastream. Simple text or XML content may be nested directly, otherwise Base64 encoding may be required. - a component is represented by a
<didl:Component>element, which contains one or more resources and may also contain any number of descriptors. - an item is represented by a
<didl:Item>element, and may contain components and/or nested items. It may also contain any number of descriptors. - a descriptor is represented by a
<didl:Descriptor>element, and contains additional information about the enclosing entity. The information may be a simple human-readable description, native identification or addressing, or any other kind of metadata. As well as standard MPEG-21 elements, arbitrary third party XML may be used in a descriptor, using third party namespaces as necessary. - a container is represented by a
<didl:Container>element, and may contain other containers, items and descriptors.
Many (all?) remaining parts of the MPEG-21 DID specification are concerned with metadata elements that may be used in descriptors in a DID.
It's hard to say at this time what makes MPEG-21 special. There are various packaging frameworks with comparable features, coming from both libgrary and computing communities: MIME, Mets, ASN.1, DOM, to name a few, and more are mentioned in the papers listed below. Being a reasonably web-friendly ISO standard for digital objects is in its favour, as this is likely to find favour for use with government and international projects. MPEG-21 can be found "under the hood" of several other projects with apparently similar aims; for example, some of the people involved in using MPEG-21 are also involved in the Pathways project.
Links
As an ISO standard, substantial parts of MPEG-21 specification are available only on payment of a fee. Some parts are freely available:
- http://standards.iso.org/ittf/PubliclyAvailableStandards/c040611_ISO_IEC_TR_21000-1_2004(E).zip - Part 1: Vision, Technologies and Strategy
- http://standards.iso.org/ittf/PubliclyAvailableStandards/c041112_ISO_IEC_21000-2_2005(E).zip - Part 2: Digital Item Declaration
- http://standards.iso.org/ittf/PubliclyAvailableStandards/MPEG-21_schema_files/ - XML schema files
Also, I learn that MPEG-21 Part 9 is based on the ISO base media file format which is a joint standard between MPEG and JPEG. The ISO base media file format is publicly available:
- http://standards.iso.org/ittf/PubliclyAvailableStandards/c041828_ISO_IEC_14496-12_2005(E).zip
- http://standards.iso.org/ittf/PubliclyAvailableStandards/c042292_ISO_IEC_14496-12_2005_Cor_1_2005(E).zip
- http://standards.iso.org/ittf/PubliclyAvailableStandards/c043226_ISO_IEC_14496-12_2005_Cor_2_2006(E).zip
- http://standards.iso.org/ittf/PubliclyAvailableStandards/c043689_ISO_IEC_14496-12_2005_Amd_1_2007(E).zip
And David Singer has said in an email: We can probably sum up what part 9 says well enough for you. It's short enough!
An MPEG-21 file has the following boxes from the public part 12 spec:
ftyp meta, whose primary item is an MPEG-21 DIDL handler, saying it's mpeg-21 item location item information and probably an mdat
See also:
- http://library.lanl.gov/cgi-bin/getfile?LA-UR-05-6633.pdf, http://arxiv.org/ftp/cs/papers/0508/0508065.pdf, Representing Digital Assets using MPEG-21 Digital Item
Declaration - seems to be a relatively recent paper fromn LANL about using MPEG-21 DID to represent digital assets, with some history of related MPEG standards.
- aDORe repository software
- Pathways project
- ACEmedia project: Autonomous Content Entity (ACE)
