D24 - Metadata Watch Report #3

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Metadata Watch Report #3

Section 2 - The concept of application profiles

The concept of application profiles has emerged in discussions on metadata schemas in the last year, in relation to work that is being done on metadata registries, specifically in the Dublin Core Metadata Initiative. The partners in the SCHEMAS project, and specifically Thomas Baker of GMD and Rachel Heery and Manjula Patel of UKOLN, have made major contributions to this discussion.

Baker, in a "strawman proposal" to the Dublin Core Registry working group [1] defines application profiles as entities that declare which elements from which namespaces underlie the local schema used in a particular application or project. In his view, application profiles "re-use" semantics from namespaces and repackage them for a particular purpose. This is in line with Heery and Patel [2] who define application profiles as schemas consisting of elements drawn from one or more namespaces, combined together and optimised for a particular application. They suggest that a distinction can be made between a namespace schema (containing all those elements defined for a particular namespace) and an application profile schema (containing combinations of sub-sets of one or more namespace schemas).

It needs to be pointed out that the term namespace in these definitions should be read as the metadata element definitions and semantics defined within those namespaces. As an example, the namespace for the Dublin Core Metadata Element Set, version 1.1 can be referred to (in XML) as:

xmlns:dc= "http://purl.org/dc/elements/1.1/

At the location specified by the URL, the 15 Dublin Core elements and their semantics are defined.

In his "strawman proposal" and in subsequent discussions, Baker laid out a number of functional requirements for application profiles:

to declare which elements from which namespaces an application or application community is using in its project- or domain-specific schema.
to override the default (i.e., standard) definition or label of a particular element (from the namespace) with a definition or label that makes sense in the local context. For example, a profile for an application for describing collections might redefine the Dublin Core element Title -- officially, "A name given to the resource" -- with a more restricted local definition: "A name given to the collection".
to describe the project or application to which it refers. At a minimum, this description should give the name and mission of a project or application. Ideally, it would provide further technical detail about the application environment in which the schema is used.
to specify dependencies among vocabulary terms -- for example (in profiles that use Dublin Core), that particular encoding schemes may be used with particular elements.
to define multiple entity classes in a particular data model. For example, a given application may need to describe both "people" (with attributes like name, occupation, and weight) and "resources" (with attributes like title, subject, and format).
to provide guidelines, in free text, about the local use of particular terms.
to express controlled vocabularies in a machine-understandable way. For example, if the values of the term "Economic Sector" are restricted to just "Agriculture", "Industry", or "Services", the profile should be able to declare this.

to specify the language and the character encoding (e.g. Big-5 encoding for Chinese) of the human-readable parts well enough to aloow these to be rendered in the correct font.

It needs to be noted that this is very much ‘work in progress’ and that these requirements may evolve over time, before there is a general agreement.

The SCHEMAS project adopted the following definition at the occasion of the second workshop [3]:

Implementation projects generally find that no one metadata standard will completely meet their descriptive needs. General standards such as Dublin Core must often be used alongside domain- or sector-specific standards such as MPEG-7 for multimedia and IEEE/LOM for educational resources; and new elements may be needed for local needs not covered by any of the existing standards. Recent practice distinguishes between the definition of semantics in "namespaces" (i.e. official standards) and the reuse and interpretation of those semantics in "application profiles". Application profiles are schemas that combine elements from multiple standards, perhaps with application-specific constraints such as the use of specific controlled vocabulary.

Maintained by: UK Office for Library and Information Networking (UKOLN)
Last updated: 13 June 2001