The Moving Picture Experts Group

Digital Item Identification

Part number: 
Activity status: 

MPEG-21 Digital Item Identification (DII)


MPEG doc#: N7423
Date: July 2005
Author: Niels Rump


1         Overview

Identification systems are fundamental components of any commerce system. This applies to the physical world and – maybe even more so – to the digital content ecommerce environment. Various content identifiers either exist today or are under development.

If MPEG-21 is to be used in an ecommerce environment, it is essential that such identifiers can be associated with Digital Items. Moreover, as Digital Items can be structured entities (see ISO/IEC 21000-2) that may contain other entities, it will be necessary to also enable the association of identifiers with parts of Digital Items.

This function is performed by ISO/IEC 21000-3, Digital Item Identification (DII) by providing a method to use existing identification schemes to identify Digital Items. It is not a new identification scheme by itself. For example it does not attempt to replace the ISRC (as defined in ISO 3901) for sound recordings. Instead it relies on existing schemes (such as ISRC) and provides a uniform mechanism to transport industry identifiers within context of MPEG-21. Therefore the specification was developed with two issues in mind: 

  • The specification needs to be compatible with existing and future identification schemes; and
  • The specification needs to enable use of such identifiers in the context of MPEG-21 applications.

The rationale behind this approach is that (most) identification schemes are content domain specific. It is the stakeholders in these domains that define important issues with respect with “their” identifiers, including: 

  • Level of Granularity;
  • Scope of uniqueness;
  • Persistence;
  • Reference metadata;
  • Resolution; and
  • Governance.

 A generic technical standards organisation that develops standards for a wide range for content and content delivery industries must not interfere with such decisions but limit itself to provide support technologies.

2         Identifying Identifiers

If different identifiers are included within one Digital Item it is important to be able to recognise the identification schemes governing each identifier. For instance, to know that a Digital Item has an identifier “5-010356-663694” is meaningless unless it is known that this is an EAN bar code. While this is often clear from the context it cannot be guaranteed. Thus identification systems themselves have to be identified. ISO/IEC 21000-3 uses namespaces for this and two methods of providing such identifier namespaces; 

  • Some identifications have their own “native: namespace (e.g. the Digital Object Identifier DOI);
  • For other identifier systems a Registration Authority has been established to provide a namespace for identification systems.