Namespace Policy

Credential Transparency Description Language (CTDL)


Stuart Sutton
Jeanne Kitchens

Date Created:


Document Description:

All terms (properties & classes) used in metadata descriptions that conform to the Credential Transparency Description Language (CTDL) must be assigned a unique URI. The term URIs that are assigned and managed by Credential Engine (CE) are grouped into collections known as CTDL namespaces. This document describes how term URIs are allocated by CE and the policies associated with CTDL namespaces.


This document uses of the following terminology:




A property (RDF), class (RDFS), concept scheme (SKOS), or concept (SKOS].


A Uniform Resource Identifier (URI) or Internationalized Resource Identifier (IRI).

CTDL term

A term that is declared and maintained by CE.

term URI

The URI that identifies a term.


The URI for a term that is declared and managed by CE.

term name

A unique lexical token assigned to a  term.  For all  CTDL terms, the  term name is appended to a  CTDL namespace URI to create the  CTDL term URI.

term label

A human-readable label assigned to a term that may or may not be lexically identical to the term name.

CTDL namespace

A collection of CTDL term URIs where each term is assigned a URI that starts with the same 'base URI'. The 'base URI' is known as the CTDL namespace URI. (Note that a CTDL namespace is not the same as an 'XML namespace').

CTDL namespace URI

The URI that identifies a CTDL namespace.

CTDL term declaration

A representation of one or more CTDL terms.

 Term URIs are grouped into  CTDL namespaces in order to ease the assignment of  URIs to  terms  and to streamline their use in particular serializations. Note that the grouping of  term URIs into  CTDL namespaces is orthogonal to the grouping of  terms into sets designed to meet other functional needs, e.g., as various types of vocabularies, particular profiles, or as specific graph shapes or record structures.

1. CTDL Namespace URIs

The CTDL namespace URI (base URI) for the collection of all CTDL properties, classes and concept schemes is:

The  CTDL namespace URI (base URI) for the concept classes in the CTDL concept schemes (controlled vocabularies) are:

2. Some example CTDL term URIs the CTDL term URI for the Industry Type property. the CTDL term URI for the Digital Badge class. the CTDL term URI for the Claim Type concept scheme (vocabulary)  class. the CTDL term URI for the Badge Claim concept class in the Claim Type concept scheme.

Each CTDL term can be so identified. All CTDL term URIs will dereference to a CTDL term declaration for the identified term. A machine-processable CTDL term declaration is available.

3. Policy concerning kinds of changes to CTDL terms

Changes to  CTDL terms or  term declarations will occur from time to time for a variety of reasons. Such changes have varying implications for CTDL term URIs and CTDL namespaces. The following kinds of changes are identified along with examples and associated implications.

In all cases, any changes to CTDL terms or term declarations will result in an update to the versioning information carried in the CTDL term declaration associated with that term.

A. Minor editorial errata

Errors of spelling, punctuation, or other clerical mistakes discovered in CTDL term declarations will be corrected without a comment period, following notification to the CTDL Technical Advisory Committee (TAC), as long as, in the judgment of the CE Technical Team, there are no implications for negative impact on users or applications that rely on those CTDL term declarations. If the CE Technical Team is uncertain as to potential negative impact of such a change, a comment period will be declared on notification of the TAC.

Correction of minor editorial errata will result in no changes to CTDL term URIs.

B. Substantive editorial errata

Errors of substance discovered in a CTDL term declarations will trigger public notification of any recommended correction to the TAC mailing list. The TAC may ask for even wider public distribution of the pending change. Errors that, in the judgment of the CE Technical Team based on input from the TAC, compromise the immediate usefulness or accuracy of systems relying on the term declaration under consideration will be corrected immediately (for example, an incorrect URI to a resource external to CTDL and CE). Others will be corrected following a 14-day public comment period to assure that changes do not adversely affect systems or applications which rely on the CTDL namespace infrastructure.

Correction of substantive editorial errata will result in no changes in CTDL term URIs.

C. Semantic changes in CTDL terms

Changes of definitions within a  CTDL term declaration will be reflected in the affected  CTDL term declaration . If, in the judgment of the CE Technical Team, such changes of meaning are likely to have substantial impact on either machine processing of CTDL terms or the functional semantics of the terms, then these changes will be reflected in a change of URI for the CTDL term or terms in question. The URIs for any new CTDL namespaces resulting from such changes will conform to the CTDL namespace URI patterns defined above.

D. Addition of CTDL term declarations to existing CTDL namespaces

New CTDL term URIs will occasionally be added to existing CTDL namespaces. Addition of CTDL term URIs to existing CTDL namespaces will not trigger changes in CTDL namespace URIs.

4. Persistence Policy

Credential Engine (CE) recognizes that people and applications depend on the persistence of formal documents and machine processable schemas that have been made publicly available. In particular, the stability of CTDL term URIs and CTDL namespace URIs is critical to interoperability over time. Thus, the wide promulgation of this set of URIs dictates that they be maintained to support legacy applications that have adopted them.

Editor’s Note

The Credential Transparency Description Language (CTDL) Namespace Policy is adapted from the Namespace Policy for the Dublin Core Metadata Initiative (DCMI).