"The basic architectural concept in MPEG-21 is the Digital Item. Digital Items are structured digital objects, including a standard representation, identification and metadata. They are the basic unit of transaction in the MPEG-21 framework. More concretely, a Digital Item is a combination of resources (such as videos, audio tracks, images, etc), metadata (such as descriptors, identifiers, etc), and structure (describing the relationships between resources).
This second part of MPEG-21 (ISO/IEC 21000-2:2003) specifies a uniform and flexible abstraction and interoperable schema for declaring the structure and makeup of Digital Items. Digital Items are declared using the Digital Item Declaration Language (DIDL) and declaring a Digital Item involves specifying its resources, metadata and their interrelationships.
Within ISO/IEC 21000-2:2003 this Digital Item Declaration (DID) technology is described in four main sections:
- Model: The Digital Item Declaration Model describes a set of abstract terms and concepts to form a useful model for defining Digital Items.
- Representation: The Digital Item Declaration Language (DIDL) is based upon the terms and concepts defined in the above model. It contains the normative description of the syntax and semantics of each of the DIDL elements, as represented in XML. This section also contains some short non-normative examples for illustrative purposes.
- Schema: The complete normative XML schema for DIDL comprising the entire grammar of the DID representation. Detailed Examples: Illustrative (non-normative) examples of DIDL documents are provided to aid in understanding the use of the specification and its potential applications.
ISO/IEC 21000 (MPEG-21) defines an open framework for multimedia delivery and consumption, with both the content creator and content consumer as focal points. The vision for MPEG-21 is to define a multimedia framework to enable transparent and augmented use of multimedia resources across a wide range of networks and devices used by different communities..." [from the ISO Store description]
[June 05, 2001] The MPEG-21 'Digital Item Declaration' is "a uniform and flexible abstraction and interoperable schema for declaring Digital Items" and is one of several elements in the MPEG-21 Framework. The Digital Item Declaration Language (DIDL) provides a markup representation for the Digital Item Declaration abstract model. MPEG issued a 'Call for Proposals for Digital Item Declaration' in October 2000 inviting proponents to submit appropriate technologies based on the stated requirements. Following the evaluation of the resulting submissions, a Working Draft was developed (see ISO/IEC TR 18034-2: MPEG-21 Multimedia Framework Part 2: Digital Item Declaration). Other MPEG-21 parts include the "Digital Item Identification and Description" and the "Rights Data Dictionary and Rights Expression Language." The objectives in the Digital Item Declaration' are: "(1) To establish a uniform and flexible abstraction and interoperable schema for declaring Digital Items; (2) To ensure that media resources and descriptive data are fully separable; (3) To ensure that Digital items are open and extensible to any and all media resources types and description schemes; (4) To ensure that composite items can be constructed from other items, without losing the structure and properties of the sub-items; (5) To ensure that flexible configuration decision trees are declarable within the schema; (6) To ensure that hierarchies of containers and Digital Items can be efficiently searched and traversed; (7) To ensure that all Users can build and organise annotated hierarchical collections, including referential structures; (8) To ensure that Identification and revision of Digital Items and their components are supportable in an open and extensible manner."
[June 05, 2001] MPEG-21 Digital Item Declaration Working Document (Version 2.0). Draft version. Reference: ISO/IEC JTC 1/SC 29/WG 11 N3971. March 2001, Singapore. 89 pages. Multimedia Description Schemes (MDS) Group. Edited by Vaughn Iverson, Young-Won Song, Rik Van de Walle, Mark Rowe, Doim Chang, Ernesto Santos, and Todd Schwartz. International Organization For Standardization/Organisation Internationale Normalisation, ISO/IEC JTC 1/SC 29/WG 11, Coding of Moving Pictures and Audio. "This document describes the Digital Item Declaration technology under consideration in part 2 of the MPEG-21 standard. This technology is described in three normative sections: (1) Model: The Digital Item Declaration Model describes a set of abstract terms and concepts to form a useful model for defining Digital Items. Within this model, a Digital Item is the digital representation of 'a work', and as such, it is the thing that is acted upon (managed, described, exchanged, collected, etc.) within the model. (2) Representation: Normative description of the syntax and semantics of each of the Digital Item Declaration elements, as represented in XML. This section also contains some non-normative examples for illustrative purposes. (3) Schema: Normative XML schema comprising the entire grammar of the Digital Item Declaration representation in XML. In addition, illustrative (non-normative) examples are provided..." Section 6 supplies the formal "Digital Item Declaration XML Schema Definition" (W3C XML Schema).
Section 5 of the 2001-03 draft MPEG-21 Digital Item Declaration Working Document presents the 'Digital Item Declaration Representation'. The syntax of each element in the Digital Item Declaration Representation is specified using the constructs provided by XML Schema. "The goal of this schema is to be as flexible and general as possible, while providing the 'hooks' for higher level functionality that will allow it to serve as a key foundation in the building of higher level schema in other MPEG-21 domains (such as Identification and Description or Rights Management). DIDL documents are XML 1.0 documents. DIDL syntax is based on an abstract structure defined in the Digital Item Declaration Model. The following abstract elements defined in the Model are each represented in DIDL by a like-named DIDL element: Container, Item, Component, Anchor, Descriptor, Choice, Selection, Condition, Annotation, Assertion, Resource, Statement. For example, the abstract descriptor element in the Model is represented in DIDL by the DESCRIPTOR element. Therefore, the reader is likewise assumed to be familiar with the terms and concepts defined in the Model. A DIDL document consists of a DIDL root element with a single ITEM child element or CONTAINER child element. Thus, a DIDL document can represent either an item or a container. In addition, DIDL defines the following special element types that do not correspond to any of the Model elements: REFERENCE DECLARATIONS, and OVERRIDE. These special elements are used for specific purposes within DIDL..."
Context from the MPEG-21 'Overview' document: "The vision for MPEG-21 is to define a multimedia framework to enable transparent and augmented use of multimedia resources across a wide range of networks and devices used by different communities. Currently, multimedia technology provides the different players in the multimedia value and delivery chain (from content creators to end-users) with an excess of information and services. Access to information and services from almost anywhere at anytime can be provided with ubiquitous terminals and networks. However, no complete solutions exist that allow different communities, each with their own models, rules, procedures, interests and content formats, to interact efficiently using this complex infrastructure. Examples of these communities are the content, financial, communication, computer and consumer electronics sectors and their customers. Developing a common multimedia framework will facilitate co-operation between these sectors and support a more efficient implementation and integration of the different models, rules, procedures, interests and content formats. This will enable an enhanced user experience. The multimedia content delivery chain encompasses content creation, production, delivery and consumption. To support this, the content has to be identified, described, managed and protected. The transport and delivery of content will occur over a heterogeneous set of terminals and networks within which events will occur and require reporting. Such reporting will include reliable delivery, the management of personal data and preferences taking user privacy into account and the management of (financial) transactions. A multimedia framework is required to support this new type of multimedia usage. Such a framework requires that a shared vision, or roadmap, is understood by its architects, to ensure that the systems that deliver multimedia content are interoperable and that transactions are simplified and, if possible, automated. This should apply to the infrastructure requirements for content delivery, content security, rights management, secure payment, and the technologies enabling them -- and this list is not exhaustive..."
The Moving Picture Experts Group (MPEG) is "a working group of ISO/IEC in charge of the development of standards for coded representation of digital audio and video. Established in 1988, the group has produced MPEG-1, the standard on which such products as Video CD and MP3 are based, MPEG-2 the standard on which such products as Digital Television set top boxes and DVD are based and MPEG-4, the standard for multimedia for the web and mobility. The current thrust is MPEG-7 'Multimedia Content Description Interface' whose completion is scheduled for July 2001. Work on the new standard MPEG-21 'Multimedia Framework' has started in June 2000 and has already produced a Draft Technical Report. Several Calls for Proposals have already been issued and two working drafts on 'Digital Item Declaration' and 'Digital Item Identification and Description'..."
MPEG-21 (Multimedia framework (MPEG-21) Programme of Work Allocated to ISO/IEC SC 29/WG 11.
Information technology -- Multimedia framework (MPEG-21) -- Part 2: Digital Item Declaration. Published 2003-03-15. ISO Store, Online Catalog. The 62-page Standard (IS) is available for purchase (CHF 158,00, approx $128 US).
MPEG-21 Digital Item Declaration Working Document (Version 2.0). See the official .ZIP source file, cache.
Schema for DIDL XML Document Type. W3C XML Schema. Extracted from Section 6 of the March 2001 Part 2 Draft.
See also: MPEG Rights Expression Language
[February 12, 2004] "Using MPEG-21 DIP and NISO OpenURL for the Dynamic Dissemination of Complex Digital Objects in the Los Alamos National Laboratory Digital Library." By Jeroen Bekaert, Lyudmila Balakireva, Patrick Hochstenbach, and Herbert Van de Sompel. In D-Lib Magazine Volume 10 Number 2 (February 2004). ISSN 1082-9873. "This paper focuses on the use of NISO OpenURL and MPEG-21 Digital Item Processing (DIP) to disseminate complex objects and their contained assets, in a repository architecture designed for the Research Library of the Los Alamos National Laboratory. In the architecture, the MPEG-21 Digital Item Declaration Language (DIDL) is used as the XML-based format to represent complex digital objects. Through an ingestion process, these objects are stored in a multitude of autonomous OAI-PMH repositories. An OAI-PMH compliant Repository Index keeps track of the creation and location of all those repositories, whereas an Identifier Resolver keeps track of the location of individual complex objects and contained assets. An MPEG-21 DIP Engine and an OpenURL Resolver facilitate the delivery of various disseminations of the stored objects. While these aspects of the architecture are described in the context of the LANL library, the paper will also briefly touch on their more general applicability. In many cases the delivered assets to be hosted in the LANL Repository are 'complex' in the sense that they consist of multiple individual datastreams that form a single logical unit. For example, a scholarly article may be delivered as a bundle that consists of metadata describing the article, the article itself in PDF and ASCII format, and the references made in the article expressed in XML. The complex nature of the assets led to an investigation regarding existing approaches to represent complex digital objects using XML wrappers, which resulted in the selection of the MPEG-21 Digital Item Declaration Language (DIDL)  as the sole way to store digital assets in the LANL Repository. DIDL introduces a set of abstract concepts that, together, form a well-defined data model for complex digital objects [note 1]. Based on those abstract concepts, DIDL defines a W3C XML Schema that provides broad flexibility and extensibility for the actual representation of compliant complex digital objects... Digital assets to be hosted by the LANL Repository can, in principle, be obtained in a variety of ways including FTP, OAI-PMH harvesting, Web crawling and delivery on physical media. A prototype ingestion process has been developed that turns each obtained asset into an autonomous XML document that wraps the datastream(s) of which the asset consists. Such an XML document is named a Digital Item Declaration (DID); all LANL DIDs are compliant with the MPEG-21 DIDL specification. As such, for example, the different datastreams of the previously mentioned scholarly article will be contained in a single DID, which will physically contain and/or reference the various datastreams that make up the complex object. The DID also contains information added by the ingestion process, for example, aimed at expressing relationships between contained datastreams, the media type of datastreams, etc..."
[November 15, 2003] "Using MPEG-21 DIDL to Represent Complex Digital Objects in the Los Alamos National Laboratory Digital Library," By Jeroen Bekaert, Patrick Hochstenbach, and Herbert Van de Sompel. In D-Lib Magazine Volume 9 Number 11, November 2003). "Various XML-based approaches aimed at representing complex digital objects have emerged over the last several years. Approaches that are of specific relevance to the Digital Library community include the Metadata Encoding and Transmission Standard (METS), the IMS Content Packaging XML Binding, the Sharable Content Object Reference Model (SCORM), and the XML packaging approach developed by CCSDS Panel 2. The MPEG-21 Digital Item Declaration Language (DIDL) is another XML-packaging specification that, so far, has received little attention in the Digital Library community. This article gives a brief insight into the MPEG-21 standardization effort, and indicates its potential relevance to the Digital Library community. It also highlights major characteristics of DIDL, and details research conducted at the Research Library of the Los Alamos National Laboratory (LANL) into the applicability of DIDL for the representation of complex objects in the LANL repository. The positive outcome of this research has led to a decision to make DIDL-conformant documents the unit of storage in the LANL repository, and suggests that DIDL could also be a valuable building block for other Digital Library projects."
- [June 05, 2001] "DIDL: Packaging Digital Content." By Vaughn Iverson, Todd Schwartz, and Mark Walker. From XML.com. May 30, 2001. ['Internet applications generally fall short in their ability to transfer multimedia content. This article describes an XML vocabulary for packaging digital content, breaking the one-to-one mapping between the notion of a content item and an individual file.'] "In this article we detail the reasons for undertaking the development of a digital packaging standard and describe in depth a package manifest scheme that potentially addresses the enumerated needs. In doing so, we show how such a scheme effectively disassociates the notion of content item from individual files. We conclude by describing an XML vocabulary, the Digital Item Declaration Language (DIDL), a recently released first working draft from ISO/MPEG that will, when completed, provide standard means for packaging digital content... Today's popular Internet applications generally fall short in their ability to transfer raw resource content. The content of a web page for example may be defined as the collection of discrete resources -- bitmaps, JPEG images, text blocks, and so on -- that are aggregated within some predetermined format. The components of the web page may possess attributes and relationships that, while not explicitly part of the final, viewable form, may be critical in generating the displayed result. Information accompanying a JPEG image, for example, could be utilized in creating a photo caption. Information about the relationships among a group of images could be utilized in locating the images on the page..."