ISO/IEC 21000-2:2005

Information technology - Multimedia framework (MPEG-21) - Part 2: Digital Item Declaration

ISO/IEC 21000-2:2005 specifies: 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. Schema: Informative XML schemas illustrating complete grammars for representation of the DID in XML conforming to the normative 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. The ISO/IEC 21000 (MPEG-21) series of International Standards 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. This second part of MPEG-21 (ISO/IEC 21000-2:2005) specifies a uniform and flexible abstraction and interoperable representation for declaring the structure and makeup of Digital Items. A Digital Item Declaration (DID) involves specifying the resources, metadata, and their interrelationships for a Digital Item. A DID is done using the Digital Item Declaration Language (DIDL).

Technologies de l'information — Cadre multimédia (MPEG-21) — Partie 2: Déclaration d'article numérique

General Information

• Status: Published
• Publication Date: 05-Oct-2005
• ICS: 35.040 - Information coding
• ICS: 35.040.40 - Coding of audio, video, multimedia and hypermedia information
• Technical Committee: ISO/IEC JTC 1/SC 29 - Coding of audio, picture, multimedia and hypermedia information
• Drafting Committee: ISO/IEC JTC 1/SC 29 - Coding of audio, picture, multimedia and hypermedia information
• Current Stage: 9060 - Close of review
• Completion Date: 04-Jun-2030

Relations

• Consolidated By: ISO 21029-2:2015 - Cryogenic vessels - Transportable vacuum insulated vessels of not more than 1 000 litres volume - Part 2: Operational requirements
• Effective Date: 06-Jun-2022
• Amended By: ISO/IEC 21000-2:2005/Amd 1:2012 - Information technology - Multimedia framework (MPEG-21) - Part 2: Digital Item Declaration - Amendment 1: Presentation of digital item
• Effective Date: 18-Dec-2021
• Revises: ISO/IEC 21000-2:2003 - Information technology - Multimedia framework (MPEG-21) - Part 2: Digital Item Declaration
• Effective Date: 15-Apr-2008

Overview

ISO/IEC 21000-2:2005 - part of the MPEG-21 multimedia framework - defines the Digital Item Declaration (DID): a uniform abstraction and interoperable XML representation for declaring the structure, resources and metadata that compose a Digital Item. The standard covers three main deliverables:

• Model: an abstract set of terms and concepts for describing Digital Items (containers, items, components, resources, descriptors, fragments, anchors, statements, assertions, conditions, choice/selection, etc.).
• Representation: the Digital Item Declaration Language (DIDL) - normative XML syntax and semantics for DID constructs.
• Schema & Examples: informative XML Schema grammars and illustrative DIDL examples to aid implementation and interoperability.

Keywords: MPEG-21, Digital Item Declaration, DIDL, Digital Items, XML schema, multimedia framework.

Key Topics and Requirements

• Abstract DID Model: defines entity descriptions (container, item, component, resource, fragment, descriptor, statement, anchor, annotation, assertion, condition, choice, selection) to express structure and relationships.
• DIDL XML Representation: normative element definitions (, , , , , , , , , , , , , , , ), with syntax and semantics specified for consistent parsing and processing.
• Validation & Canonicalization: guidance on DIDL validation and canonical forms for consistent interchange.
• XML Schemas (informative): example schemas illustrating complete grammars for DIDL XML.
• Illustrative Examples: non-normative DIDL documents showing metadata interoperability and practical uses.
• Interoperability focus: aims to enable transparent use of multimedia across networks and devices.

Applications

ISO/IEC 21000-2:2005 is practical for anyone packaging, exchanging, or processing multimedia content and metadata:

• Content providers & publishers using DIDL to declare multimedia packages (audio, video, images, timed media).
• Media asset management & digital libraries for consistent item description, metadata binding and resource referencing.
• Streaming and delivery platforms that need structured descriptions of items and associated resources.
• Application developers & system architects implementing interoperable content workflows, metadata mapping, or ingestion/export pipelines.
• Archivists & preservation systems where explicit declaration of resources and fragments aids long-term management.

Keywords: media packaging, metadata interoperability, content delivery, digital asset management.

Related Standards

Part of the ISO/IEC 21000 (MPEG-21) series. Relevant companion parts include:

• Part 1 (Vision), Part 3 (Digital Item Identification), Part 5 (Rights Expression Language), Part 7 (Adaptation), Part 9 (File Format), Part 16 (Binary Format), plus others (Part 6, 8, 10, 11, 12, 15). Parts 4 and 14 noted as under preparation.

This standard is essential for implementing interoperable, XML-based multimedia item declarations within the MPEG-21 framework.

Standards Content (Sample)

INTERNATIONAL ISO/IEC
STANDARD 21000-2
Second edition
2005-10-01
Information technology — Multimedia
framework (MPEG-21) —
Part 2:
Digital Item Declaration
Technologies de l'information — Cadre multimédia (MPEG-21) —
Partie 2: Déclaration d'article numérique

Reference number
©
ISO/IEC 2005
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ii © ISO/IEC 2005 – All rights reserved

Contents Page
Foreword. v
Introduction . vi
1 Scope. 1
2 Normative references. 1
3 Terms and definitions. 2
4 Symbols and abbreviated terms . 2
5 Conventions . 3
5.1 Naming convention. 3
5.2 Documentation convention . 3
5.3 Namespace prefix conventions. 5
6 Digital Item Declaration Model . 6
6.1 Purpose and Overview . 6
6.2 Abstract Model. 6
6.2.1 Entity Descriptions . 6
6.2.2 container. 6
6.2.3 item. 6
6.2.4 component. 7
6.2.5 anchor . 7
6.2.6 descriptor . 7
6.2.7 condition. 7
6.2.8 choice. 8
6.2.9 selection . 8
6.2.10 annotation. 8
6.2.11 assertion . 8
6.2.12 resource. 8
6.2.13 fragment. 8
6.2.14 statement . 8
6.2.15 predicate . 8
7 Digital Item Declaration Representation. 10
7.1 Purpose and Overview . 10
7.1.1 Purpose. 10
7.1.2 DIDL Overview. 10
7.2 DIDL Definition . 11
7.2.1 Validation. 11
7.2.2 Canonicalization . 11
7.2.3 Document modularity. 11
7.2.4 Element Descriptions . 12
7.2.5 . 12
7.2.6 . 14
7.2.7 . 15
7.2.8 . 15
7.2.9 . 17
7.2.10 . 20
7.2.11 . 22
7.2.12 . 25
7.2.13 . 27
7.2.14 . 31
7.2.15 . 34
© ISO/IEC 2005 – All rights reserved iii

7.2.16 . 37
7.2.17 . 38
7.2.18 . 41
7.2.19 . 42
7.2.20 . 45
8 The Digital Item Declaration XML Schema Definitions (informative). 46
8.1 Purpose and Overview . 46
8.2 DID Model Abstract Schema . 47
8.3 DIDL Schema. 49
9 Example Digital Items expressed in DIDL . 57
9.1 Example 1: Using MPEG-7 descriptors in conjunction with a Choice. 57
9.2 Example 2: Expressing the same set of metadata in different descriptor formats. 59
9.3 Example 3: A digital music album. 60
9.4 Example 4: Implementing numeric comparisons in Item configuration . 78
Annex A (informative) Patent statements . 81
Annex B (informative) Differences with ISO/IEC 21000-2:2003. 82
B.1 Introduction . 82
B.2 Attribute-based descriptors. 82
B.3 . 82
B.4 . 82
B.5 and . 83
B.6 . 83
B.7 and XInclude. 83
B.8 Schema definitions . 85
B.9 Converting a first edition DIDL document to a second edition DIDL document . 86
Bibliography . 88

iv © ISO/IEC 2005 – All rights reserved

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are members of
ISO or IEC participate in the development of International Standards through technical committees
established by the respective organization to deal with particular fields of technical activity. ISO and IEC
technical committees collaborate in fields of mutual interest. Other international organizations, governmental
and non-governmental, in liaison with ISO and IEC, also take part in the work. In the field of information
technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of the joint technical committee is to prepare International Standards. Draft International
Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as
an International Standard requires approval by at least 75 % of the national bodies casting a vote.
ISO/IEC 21000-2 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 29, Coding of audio, picture, multimedia and hypermedia information.
This second edition cancels and replaces the first edition (ISO/IEC 21000-2:2003), which has been technically
revised.
ISO/IEC 21000 consists of the following parts, under the general title Information technology — Multimedia
framework (MPEG-21):
⎯ Part 1: Vision, Technologies and Strategy [Technical Report]
⎯ Part 2: Digital Item Declaration
⎯ Part 3: Digital Item Identification
⎯ Part 5: Rights Expression Language
⎯ Part 6: Rights Data Dictionary
⎯ Part 7: Digital Item Adaptation
⎯ Part 8: Reference Software
⎯ Part 9: File Format
⎯ Part 10: Digital Item Processing
⎯ Part 11: Evaluation Tools for Persistent Association Technologies [Technical Report]
⎯ Part 12: Test Bed for MPEG-21 Resource Delivery [Technical Report]
⎯ Part 15: Event Reporting
⎯ Part 16: Binary Format
The following parts are under preparation:
⎯ Part 4: Intellectual Property Management and Protection Components
⎯ Part 14: Conformance Testing
© ISO/IEC 2005 – All rights reserved v

Introduction
Today, many elements exist to build an infrastructure for the delivery and consumption of multimedia content.
There is, however, no “big picture” to describe how these elements, either in existence or under development,
relate to each other. The aim for MPEG-21 is to describe how these various elements fit together. Where gaps
exist, MPEG-21 will recommend which new standards are required. ISO/IEC JTC 1/SC 29/WG 11 (MPEG) will
then develop new standards as appropriate while other relevant standards may be developed by other bodies.
These specifications will be integrated into the multimedia framework through collaboration between MPEG
and these bodies.
The result is an open framework for multimedia delivery and consumption, with both the content creator and
content consumer as focal points. This open framework provides content creators and service providers with
equal opportunities in the MPEG-21 enabled open market. This will also be to the benefit of the content
consumer providing them access to a large variety of content in an interoperable manner.
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.
This second part of MPEG-21 (ISO/IEC 21000-2) specifies the mechanism for declaring the structure and
makeup of Digital Items.
The International Organization for Standardization (ISO) and International Electrotechnical Commission (IEC)
draw attention to the fact that it is claimed that compliance with this document may involve the use of a patent.
The ISO and IEC take no position concerning the evidence, validity and scope of this patent right.
The holder of this patent right has assured the ISO and IEC that he is willing to negotiate licences under
reasonable and non-discriminatory terms and conditions with applicants throughout the world. In this respect,
the statement of the holder of this patent right is registered with the ISO and IEC. Information may be obtained
from the companies listed in Annex A.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights other than those identified in Annex A. ISO and IEC shall not be held responsible for identifying any or
all such patent rights.
vi © ISO/IEC 2005 – All rights reserved

INTERNATIONAL STANDARD ISO/IEC 21000-2:2005(E)

Information technology — Multimedia framework (MPEG-21) —
Part 2:
Digital Item Declaration
1 Scope
This document describes the ISO/IEC 21000 Digital Item Declaration technology, which is Part 2 of the
ISO/IEC 21000 series of International Standards. It specifies:
⎯ the Digital Item Declaration Model (see 6),
⎯ the Digital Item Declaration Representation in XML (see 7), and
⎯ XML schemas comprising grammars for the Digital Item Declaration representation in XML (see 8).
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO/IEC 21000 (all parts), Information Technology — Multimedia Framework (MPEG-21)
IETF RFC 2045, Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies,
IETF Request for Comments: 2045, November 1996
IETF RFC 2616, Hypertext Transfer Protocol – HTTP/1.1, IETF Request for Comments: 2616, June 1999
IETF RFC 3548, The Base16, Base32, and Base64 Data Encodings, IETF Request for Comments: 3548,
July 2003
IETF RFC 3986, Uniform Resource Identifier (URI): Generic Syntax, IETF Request For Comments: 3986,
January 2005
W3C XINCLUDE, XML Inclusions (XInclude) Version 1.0, W3C Recommendation, 20 December 2004
W3C XML, Extensible Markup Language 1.0 (Second Edition), W3C Recommendation, 6 October 2000
W3C XMLC14N, Canonical XML Version 1.0, W3C Recommendation, 15 March 2001
W3C XMLNAMES, Namespaces in XML, W3C Recommendation, 14 January 1999
W3C XMLSCHEMA, XML Schema Part 1: Structures Second Edition and XML Schema Part 2: Datatypes
Second Edition, W3C Recommendations, 28 October 2004
© ISO/IEC 2005 – All rights reserved 1

3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
Abstraction
distinct intellectual or artistic creation or concept
[ISO/IEC TR 21000-1:2004]
3.2
Asset
Manifestation, i.e. physical or digital embodiment of an Expression
[ISO/IEC TR 21000-1:2004]
3.3
Digital Item
a structured digital object with a standard representation, identification and metadata within the MPEG-21
framework
NOTE This entity is the fundamental unit of distribution and transaction within the MPEG-21 framework as a whole; it
has, however, no further technical meaning. Within this document (part 2 of MPEG-21: Digital Item Declaration), an item is
a grouping of sub-items and/or components that are bound to relevant descriptors, as defined within the Digital Item
Declaration Model (see 6). The term item is a technical term, and is, as such, a narrower term than Digital Item. In
conclusion, the use of the two different terms Digital Item and item within MPEG-21 is consistent and intended.
3.4
Expression
intellectual or artistic realisation of an Abstraction
[ISO/IEC TR 21000-1:2004]
3.5
Manifestation
the physical or digital embodiment of an Expression
[ISO/IEC TR 21000-1:2004]
4 Symbols and abbreviated terms
For the purposes of this document, the following abbreviations apply.
DID: Digital Item Declaration
DIDL: Digital Item Declaration Language
EBNF: Extended Backus-Naur Form
IANA:  Internet Assigned Numbers Authority
IETF:  Internet Engineering Task Force
IPMP: Intellectual Property Management and Protection
JPEG:  Joint Photographic Experts Group
MIME:  Multipurpose Internet Mail Extensions (IETF RFC 2045)
2 © ISO/IEC 2005 – All rights reserved

MPEG:  Moving Picture Experts Group
MPEG-21: ISO/IEC 21000 (all parts)
MPEG-7: ISO/IEC 15938
MP3:  MPEG-1/2 layer III (audio coding)
RFC:  Request for Comments
SVG:  Scalable Vector Graphics
URI:  Uniform Resource Identifier (IETF RFC 3986)
URL:  Uniform Resource Locator (IETF RFC 3986)
URN:  Uniform Resource Name (IETF RFC 3986)
W3C:  World Wide Web Consortium
XML:  Extensible Markup Language (W3C XML)
5 Conventions
5.1 Naming convention
It should be noted that the Digital Item Declaration Model (clause 6) contains the concept names that are used
throughout the MPEG-21 standard. As such, this model should be considered to be the “ultimate arbiter” of
these MPEG-21 concept names.
5.2 Documentation convention
The semantics of each entity in the Digital Item Declaration Model is specified using the constructs provided
by EBNF [4], and is shown in this document using a specific font and background:
entity ::= (part1 | part2)+ part3*
The syntax of each element in the Digital Item Declaration Representation is specified using the constructs
provided by XML Schema [2].
Element names and attribute names in the representation are in SMALL CAPS. Throughout the document, italics
are used when referring to entities defined in the Digital Item Declaration Model (see clause 4), hereafter
known as the Model.
The syntax of each element in the Digital Item Declaration representation is specified using the following
format.
© ISO/IEC 2005 – All rights reserved 3

Table 1 — Example element specification

Diagram
Children
Used by
Name Type Description
Attributes
ID ID A unique ID value, which can be referenced by another element.






Source  







The Language Definition clause contains syntax diagrams for each element. Here is an example syntax
diagram with annotations:
4 © ISO/IEC 2005 – All rights reserved

Optional child
Sequence group
Required child
Parent element
Optional
unbounded
child
Required
unbounded
Choice group
child
Required child
with children
Figure 1 — Example element syntax diagram
Non-normative examples are included in separate clauses, and are shown in this document using a separate
font and background:

example element content

5.3 Namespace prefix conventions
This document makes use of vocabularies from several XML namespaces (where the definition of an XML
namespace is as specified in W3C XMLNAMES [7]). Qualified Names are written with a namespace prefix
followed by a colon followed by the local part of the Qualified Name as shown in the following example.
EXAMPLE didl:DIDL
For the purposes of this document the Table below gives the namespace prefixes associated with the
identified namespaces.
Table 2 — Namespace prefixes
Namespace prefix Namespace
didmodel urn:mpeg:mpeg21:2002:02-DIDMODEL-NS
didl urn:mpeg:mpeg21:2002:02-DIDL-NS
dii urn:mpeg:mpeg21:2002:01-DII-NS
mx urn:mpeg:mpeg21:2003:01-REL-MX-NS
sx urn:mpeg:mpeg21:2003:01-REL-SX-NS
dia urn:mpeg:mpeg21:2003:01-DIA-NS
diac urn:mpeg:mpeg21:2003:01-DIA-DIAC-NS
© ISO/IEC 2005 – All rights reserved 5

mpeg7 urn:mpeg:mpeg7:schema:2001
dsig http://www.w3.org/2000/09/xmldsig#
rdf http://www.w3.org/1999/02/22-rdf-syntax-ns#
xml
http://www.w3.org/XML/1998/namespace
xi http://www.w3.org/2001/XInclude
xsd http://www.w3.org/2001/XMLSchema
xsi http://www.w3.org/2001/XMLSchema-instance
dc http://purl.org/dc/elements/1.1/
uaprof http://www.wapforum.org/profiles/UAPROF/ccppschema-20000405
foo
This namespace prefix is used for demonstration only.

6 Digital Item Declaration Model
6.1 Purpose and Overview
The purpose of this clause is to describe 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 an Asset, and as such, it
is the unit that is acted upon (managed, described, exchanged, collected, etc.) within the model. The goal of
this model is to be as flexible and general as possible, while providing for the “hooks” that enable higher level
functionality. This, in turn, allows the model to serve as a key foundation in the building of higher level models
in other MPEG-21 elements (such as Identification or IPMP). This model specifically does not define a
language in and of itself. Instead, the model helps to provide a common set of abstract concepts and terms
that can be used to define such a scheme, or to perform mappings between existing schemes capable of
Digital Item Declaration, for comparison purposes.
6.2 Abstract Model
6.2.1 Entity Descriptions
In the following descriptions, the defined entities in italics are intended to be unambiguous terms within this
model. The prose descriptions define the semantic “meaning” of the terms, and the EBNF representations
define the precise intended relationship or structure between terms within the model.
6.2.2 container
A container is a structure that allows items and/or containers to be grouped. These groupings of items and/or
containers can be used to form logical packages (for transport or exchange) or logical shelves (for
organization). Descriptors allow for the “labelling” of containers with information that is appropriate for the
purpose of the grouping (e.g. delivery instructions for a package, or category information for a shelf).
It should be noted that a container itself is not an item; containers are groupings of items and/or containers.
container ::= descriptor* container* item*
6.2.3 item
An item is a grouping of sub-items and/or components that are bound to relevant descriptors. Descriptors
contain information about the item, as a representation of an Asset. Items may contain choices, which allow
them to be customized or configured. Items may be conditional (on predicates asserted by selections defined
6 © ISO/IEC 2005 – All rights reserved

in the choices). An item that contains no sub-items can be considered a whole -- a logically indivisible Asset.
An item that does contain sub-items can be considered a compilation -- an Asset composed of potentially
independent sub-parts. tems may also contain annotations to their sub-parts.
The relationship between items and Digital Items (as defined in ISO/IEC 21000-1:2001, MPEG-21 Vision,
Technologies and Strategy) could be stated as follows: items are declarative representations of Digital Items.
item ::= condition* descriptor* choice* (item | component)* annotation*
6.2.4 component
A component is the binding of a resource to a set of descriptors. These descriptors are information concerning
all or part of the specific resource instance. Such descriptors will typically contain control or structural
information about the resource (such as bit rate, character set, start points or encryption information) but not
information describing the “content” within.
It should be noted that a component itself is not an item; components are building blocks of items.
component ::= condition* descriptor* resource anchor*
6.2.5 anchor
An anchor binds descriptors to a fragment, which corresponds to a specific location or part of a resource.
These descriptors are information concerning all or part of the fragment.
anchor ::= condition* descriptor* fragment
6.2.6 descriptor
A descriptor associates information with the enclosing entity. This information may be a component (such as a
thumbnail of an image, or a text component), or a textual statement.
NOTE Though a descriptor associates information with the enclosing entity, that information does not always
directly concern the enclosing entity. The enclosing entity specifies what the associated information concerns.
(For example, a descriptor in a component, associates information with a component that concerns the
resource in that component.)
descriptor ::= condition* descriptor* (component | statement)
6.2.7 condition
A condition describes the enclosing entity as being optional, and links it to the selection(s) that affect its
inclusion. Multiple predicates within a condition are combined as a conjunction (an AND relationship). Any
predicate may be negated within a condition. Multiple conditions associated with a given entity are combined
as a disjunction (an OR relationship) when determining whether to include the entity.
condition ::= predicate+
© ISO/IEC 2005 – All rights reserved 7

6.2.8 choice
A choice describes a set of related selections that can affect the configuration of an item. The selections within
a choice are either exclusive (choose exactly one) or inclusive (choose any number, including all or none).
choice ::= condition* descriptor* selection+
6.2.9 selection
A selection describes a specific decision that will affect one or more conditions somewhere within an item. If
the selection is chosen, its predicate becomes true; if it is not chosen, its predicate becomes false; if it is left
unresolved, its predicate is undecided.
selection ::= condition* descriptor* predicate
6.2.10 annotation
An annotation describes a set of information about another identified entity of the model without altering or
adding to that entity. The information can take the form of assertions, descriptors, and anchors.
annotation ::= assertion* descriptor* anchor*
6.2.11 assertion
An assertion defines a full or partially configured state of a choice by asserting true, false or undecided values
for some number of predicates associated with the selections for that choice.
assertion ::= predicate*
6.2.12 resource
A resource is an individually identifiable Asset such as a video or audio clip, an image, or a textual Asset. A
resource may also potentially be a physical object. All resources shall be locatable via an unambiguous
address.
6.2.13 fragment
A fragment unambiguously designates a specific point or range within a resource. Fragment may be resource
type specific.
6.2.14 statement
A statement is a literal textual value that contains information, but not an Asset. Examples of likely statements
include descriptive, control, revision tracking or identifying information (such as an identifier as described in
ISO/IEC 21000-3).
6.2.15 predicate
A predicate is an unambiguously identifiable declaration that can be true, false or undecided.
8 © ISO/IEC 2005 – All rights reserved

The following diagram is an example showing the most important entities within this model, how they are
related, and as such, the hierarchical structure of the Digital Item Declaration Model.
Container
Item Item
Descriptor Descriptor
Component Component
Descriptor
Descriptor
Resource Resource
Component
Item
Descriptor
Descriptor
Resource
Component
Descriptor
Resource
Item
Component
Descriptor
Resource
Figure 2 — Example Digital Item Declaration model
© ISO/IEC 2005 – All rights reserved 9

7 Digital Item Declaration Representation
7.1 Purpose and Overview
7.1.1 Purpose
The purpose of this clause is to describe the syntax and semantics of the W3C XML representation for
declaring Digital Items. The syntax is defined using XML schema (as specified in W3C XMLSCHEMA). The
goal 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 or Rights Management). For the purposes of this document, the XML schema syntax
descriptions are collectively referred to as DIDL schema.
7.1.2 DIDL Overview
DIDL documents are W3C XML 1.0 [1] documents. The reader is assumed to be familiar with the terms and
concepts of XML 1.0.
In addition, DIDL syntax is based on an abstract structure defined in the Digital Item Declaration Model (see
clause 6 above). The following abstract entities defined in the Model are each represented in DIDL by a like-
named DIDL element:
⎯ container
⎯ item
⎯ component
⎯ anchor
⎯ fragment
⎯ descriptor
⎯ choice
⎯ selection
⎯ condition
⎯ annotation
⎯ assertion
⎯ resource
⎯ statement
For example, the abstract descriptor entity 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 type that does not correspond to any of the Model
entities: DECLARATIONS. This special element is used for specific purposes within DIDL.
10 © ISO/IEC 2005 – All rights reserved

The DECLARATIONS element is used to define a set of DIDL elements in a document without actually
instantiating them. A declared element (i.e. a child element of a DECLARATIONS element) is not considered to
be instantiated unless it is referenced (by an XInclude include element).
DIDL makes broad use of XML’s ID attribute type. Generally, attributes of this type are used to make an
internal association between one DIDL element and another. For example, many DIDL elements have an ID
attribute, which makes them available as targets of internal references (see 7.2.3) by XInclude include
elements, and, in limited cases, available for annotation by ANNOTATION elements. In addition, other attributes
of type ID that are not named ‘id’ are used to make specific kinds of associations between specific elements.
For example, the SELECT_ID attribute of the SELECTION element allows CONDITION elements to be associated
with specific SELECTIONS. It is strongly recommended that attributes of type ID be assigned globally unique
values, in order to avoid collisions when DIDL documents are merged. This is especially important when there
are external dependencies on the ID values, such as a signature on the DIDL document, or an external
reference from some other document or resource. Finally, it is noted that the use of the ID attribute should not
be confused with normative identification mechanisms defined in any other part of ISO/IEC 21000.
7.2 DIDL Definition
7.2.1 Validation
Validating a document against the DIDL schema (as specified in W3C XMLSCHEMA) is necessary, but not
sufficient, to determine its validity with respect to DIDL. After a document is validated against the DIDL
schema, it shall also be subjected to additional validation rules. These additional rules are given below in the
descriptions of the elements to which they pertain.
7.2.2 Canonicalization
Like any XML document, a single logical DIDL document can be manifested in a wide variety of syntactic
representations. Although the various syntactic representations each contain a different sequence of
characters, they are all logically equivalent. In certain applications, such as generating a digest value for a
digital signature on all or part of a DIDL document, it is necessary to define a method for generating a single
predictable (deterministic) syntactic representation. Achieving this result for DIDL documents containing
internal references requires special consideration. The following canonicalization method takes this
consideration into account:
Canonical XML 1.0 [3] (as specified in W3C XMLC14N) with the following additional constraint:
All internal references are syntactically resolved; that is, the logical replacement is reflected in the
Canonical syntactic representation. The XInclude include tags corresponding to internal references are
removed in this process.
This canonicalization method is identified by the following URN: “urn:mpeg:mpeg21:2002:02:did-
canonicalization". This URN identifier is for use by any part of ISO/IEC 21000 that requires canonicalization,
or by any other application with similar requirements.
7.2.3 Document modularity
NOTE 1 Modularity of DIDL documents can be achieved by utilising XML Inclusions (XInclude) as specified in
W3C XINCLUDE [7]. XInclude can be used to reference elements within a document, or to elements in a
different document. The former type of reference is known as an internal reference; the latter is known as an
external reference. An internal reference allows a single source to be maintained for an element that occurs in
more than one place in a DIDL document. An external reference allows a DIDL document to be split up into
multiple linked discrete documents.
NOTE 2 XInclude addresses the same requirements previously addressed by the REFERENCE element in the first
edition of this part of ISO/IEC 21000. For this reason no effort is made to enable use of xml:base and xml:lang on DIDL
elements other than those for which use of REFERENCE was allowed in the first edition of this part of ISO/IEC 21000.
© ISO/IEC 2005 – All rights reserved 11

NOTE 3 There are some differences in the provision of this functionality through the use of XInclude instead of the
REFERENCE element. See Annex B for a list of the key differences.
7.2.4 Element Descriptions
The following basic principles apply to all element types:
⎯ Wherever DESCRIPTOR children are allowed, they are always the first children (except where preceded by
CONDITION).
7.2.5
The DIDL element is the root element of a DIDL instance document. The DIDL root element may contain an
optional DECLARATIONS element, followed by exactly one CONTAINER or ITEM.
The DIDL element shall include a namespace declaration that declares the DIDL namespace for the root DIDL
element and its contents. This is required so that applications will recognize the document as a DIDL
document, that is covered by this specification. The DIDL namespace URI is "urn:mpeg:mpeg21:2002:02-
DIDL-NS". The "02" represents a serial number that is expected to change as the DIDL schema evolves along
with this part of ISO/IEC 21000.
The namespace declaration may take the form of a default namespace declaration, or a prefix-specific
namespace declaration, as shown respectively in the following two examples:
EXAMPLE 1 Default namespace declaration

...

EXAMPLE 2 Prefix-specific namespace declaration

...

NOTE In this part of ISO/IEC 21000 the namespace prefix didl will be used to map to the namespace
urn:mpeg:mpeg21:2002:02-DIDL-NS, however this mapping is not normative.
The DIDL element may have an optional DIDLDOCUMENTID attribute. This attribute can be used to convey the
URI of the DIDL document. Identifiers of the Digital Items declared within the DIDL document shall not be
conveyed in this attribute.
The DIDL element may have any attributes from other namespaces. Applications that do not understand any
such attributes may ignore those attributes. Since the DIDL element is not part of the DID abstract model, it is
only valid for information regarding the DIDL document to be contained in any such attributes. Information
about the Digital Item represented by the DID shall not be conveyed in such attributes.
12 © ISO/IEC 2005 – All rights reserved

Table 3 — DIDL element syntax
Diagram
Children
Name Type Description
Attributes
DIDLDocumentId anyURI A URI of the DIDL document.







Source







© ISO/IEC 2005 – All rights reserved 13

7.2.6
The DIDLINFO element allows information applicable only to the DIDL document to be included in the DIDL
document. Since it is not part of the DID abstract model, it shall not contain information about the Digital Item
represented by the DID. An example of such information might be the digital signature for the DIDL document.
Applications that do not understand any information included in a DIDLINFO element may ignore such
information.
Table 4 — DIDLINFO element syntax
Diagram
Used by



Source




14 © ISO/IEC 2005 – All rights reserved

7.2.7
The DECLARATIONS element is used to define a set of DIDL elements - without instantiating them - for later use
in a document via an internal reference (see 7.2.3).
Table 5 — DECLARATIONS element syntax
Diagram
Children
Used by




Source  
...