Asset Description Metadata Schema (ADMS)

W3C Working Group Note 01 August 2013 (Retired August 2023)

This version:
Latest published version:
Previous version:
Phil Archer , W3C / ERCIM
Gofran Shukair , DERI, NUIG
Makx Dekkers , AMI Consult (original document)

The vocabulary defined in this document is also available in these non-normative formats: RDF/XML and Turtle.


Status Update (August 2023): The ADMS Vocabulary is now maintained by the SEMIC community and lives at https://uri.semic.eu/w3c/ns/adms. The RDF version of the legacy ADMS vocabulary (as described in this note) is available at https://www.w3.org/ns/legacy_adms.

ADMS is a profile of DCAT, used to describe semantic assets (or just 'Assets'), defined as highly reusable metadata (e.g. xml schemata, generic data models) and reference data (e.g. code lists, taxonomies, dictionaries, vocabularies) that are used for eGovernment system development.

Status of This Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

This document was published by the Government Linked Data Working Group as a Note. If you wish to make comments regarding this document, please send them to public-gld-comments@w3.org (subscribe, archives). All feedback is welcome.

The only changes made since the previous version of this document concern the acknowledgements section. No substantive changes have been made.

Publication as a Working Group Note does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Table of Contents

1. Introduction

This section is non-normative.

ADMS, the Asset Description Metadata Schema, is a profile of DCAT [ DCAT ] for describing so-called Semantic Assets (or just 'Assets'), that is, highly reusable metadata (e.g. xml schemata, generic data models) and reference data (e.g. code lists, taxonomies, dictionaries, vocabularies) that are used for eGovernment system development [ TOGD ]. Someone searching for an Asset is likely to have different needs, priorities and expectations than someone searching for a dataset in a data catalog and these differences are reflected in ADMS. In particular, users seeking an Asset are likely to be searching for a document — something they can open and read using familiar desktop software, as opposed to something that needs to be processed. Of course this is a very broad generalization. If a code list is published as a SKOS Concept scheme then it is both an Asset and a dataset and it can be argued that all Assets are datasets. Therefore the difference in user expectation is at the heart of what distinguishes ADMS as a profile of DCAT. A further distinction between DCAT and ADMS can be made in that DCAT is designed to facilitate interoperability between data catalogs , i.e. the catalog itself is at the heart of the vocabulary. ADMS is focused on the assets within a catalog.

2. Conformance

As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.

The key words must , must not , required , should , should not , recommended , may , and optional in this specification are to be interpreted as described in [ RFC2119 ].

A data interchange, however that interchange occurs, is conformant with ADMS if:

A conforming data interchange:

An ADMS profile is a specification for data interchange that adds additional constraints. Such additional constraints in a profile may include (but are not limited to):

ADMS is technology-neutral and a publisher may use any of the terms defined in this document encoded in any technology although RDF and XML are preferred.

3. Namespaces

This section is non-normative.

The namespace for ADMS is http://www.w3.org/ns/adms# . However, it should be noted that ADMS makes extensive use of terms from other vocabularies, in particular Dublin Core [ DC11 ]. It re-uses and subclasses DCAT wherever possible and therefore defines a minimal set of classes and properties of its own. A full set of namespaces and prefixes used in this document is shown in the table below.

Prefix Namespace
adms http://www.w3.org/ns/adms#
dcat http://www.w3.org/ns/dcat#
dcterms http://purl.org/dc/terms/
foaf http://xmlns.com/foaf/0.1/
schema http://schema.org/
rdfs http://www.w3.org/2000/01/rdf-schema#
skos http://www.w3.org/2004/02/skos/core#
v http://www.w3.org/2006/vcard/ns#
wdrs http://www.w3.org/2007/05/powder-s#
xhv http://www.w3.org/1999/xhtml/vocab#

4. Vocabulary Overview

This section is non-normative.

ADMS is intended as a model that facilitates federation and co-operation. Like DCAT, ADMS has the concepts of a repository (catalog), assets within the repository that are often conceptual in nature, and accessible realizations of those assets, known as distributions. An asset may have zero or multiple distributions. As an example, a W3C namespace document can be considered to be a Semantic Asset that is typically available in multiple distributions, typically one or more machine processable versions and one in HTML for human consumption. An asset without any distributions is effectively a concept with no tangible realization, such as a planned output of a working group that has not yet been drafted.

ADMS is an RDF vocabulary with an RDF schema available at its namespace http://www.w3.org/ns/adms . The original ADMS specification published by the European Commission [ ADMS1 ] includes an XML schema that also defines all the controlled vocabularies and cardinality constraints associated with the original document.

4.1 Example

This example provides a quick overview of how ADMS might be used to represent a Semantic Asset Repository and its assets.

Examples in this document are serialized in Turtle .

First, the repository description:

:Repository a adms:AssetRepository ;
  dcterms:created "1947-02-07"^^xsd:date ;
  dcterms:description "A complete catalog of code lists and standards created by the Exemplary Standards Body"@en ;
  dcterms:publisher <http://example.com/data#org> ;
  dcterms:title "The Exemplary Standards Body Catalog"@en .

This assumes that the Exemplary Standards Body is described at http://example.com/data#org .

Next, an Asset. We'll create an imaginary code list called 'Fruit I like' for our example:

We might describe this Asset thus:

1  :Fruit_02 a adms:Asset ;
2    dcterms:created "1999-05-24" ;
3    dcterms:description "Fruits that are found to be generally liked by most people." ;
4    dcterms:publisher <http://example.com/data#org> ;
5    dcterms:title "Fruit I like"@en ;
6    adms:status <http://purl.org/adms/status/Completed> ;
7    dcterms:type <http://purl.org/adms/assettype/CodeList> ;
8    adms:previous :Fruit_01 ;
9    adms:last :Fruit ;
10   dcat:distribution :Fruit_02.csv ;
11   dcat:distribution :Fruit_02.xml .

This provides the creation date (line 2), description (line 3), publisher (line 4) and a title (line 5) for the Asset. The status of the Asset is given in line 6 using one of the values made available in the original ADMS specification [ ADMS1 ]. Likewise the type of Asset in line 7. In line 8 we can see that there was a previous version of this asset (Fruit_01) and that the latest version can be found by appending 'Fruit' to the data's root (line 9).

This Asset has two distributions linked in lines 11 and 12. One of these might be described thus:

:Fruit_02.xml a adms:AssetDistribution ;
  dcterms:description "XML encoding of Fruits that are found to be generally liked by most people." ;
  dcterms:license <http://creativecommons.org/licenses/by/3.0/> ;
  dcterms:format <http://purl.org/NET/mediatypes/application/xml> .

This is a very simple description of the Asset Distribution that just gives its description, format, and license. In this example we've used Ed Summers' media types application to provide a URI for the XML MIME type [ EDSU ]

The missing triple from this example is the one that includes the Asset in the Repository. This is done with a simple triple:

:Repository dcat:dataset :Fruit_02 .

5. The ADMS Domain Model

UML Diagram of ADMS
UML model of ADMS classes and properties

The classes and properties are described in the following sub-sections

5.1 The Primary Concepts

5.1.1 Asset Repository

A system or service that provides facilities for storage and maintenance of descriptions of Assets and Asset Distributions, and functionality that allows users to search and access these descriptions. An Asset Repository will typically contain descriptions of several Assets and related Asset Distributions.

adms:AssetRepository is a sub class of dcat:Catalog

5.1.2 Asset

An abstract entity that reflects the intellectual content of the asset and represents those characteristics of the asset that are independent of its physical embodiment. This abstract entity combines the FRBR entities work (a distinct intellectual or artistic creation) and expression (the intellectual or artistic realization of a work) [ FRBR ].

Assets can be versioned. Every time the intellectual content of an asset changes, the result is considered to be a new asset that can be linked to previous and next versions of the Asset.

The physical embodiment of an Asset is called an Asset Distribution. A particular Asset may have zero or more Distributions.

adms:Asset is a sub class of dcat:Dataset

Assets are included in Repositories using DCAT's dcat:dataset property.

5.1.3 Asset Distribution

A particular physical embodiment of an Asset, which is an example of the FRBR entity manifestation (the physical embodiment of an expression of a work).

A Distribution is typically a downloadable computer file (but in principle it could also be a paper document or API response) that implements the intellectual content of an Asset.

A particular Distribution is associated with one and only one Asset, while all Distributions of an Asset share the same intellectual content in different physical formats.

Distributions themselves are not versioned. If Distribution 1A is the manifestation of Asset 1 and Distribution 2A is the manifestation of Asset 2, a version relationship will be expressed between Asset 1 and Asset 2, not between Distribution 1A and Distribution 2A. For an illustration of two Assets that each have two Distributions (representations in different formats) see the diagram below.

Diagram showing that Assets are versioned, Distributions are not
The relationship between versioned Assets and their Distributions

adms:AssetDistribution is a sub class of dcat:Distribution

Assets are linked to Asset Distributions using DCAT's dcat:distribution property.

Examples of the relationship between Assets and Asset Distributions are:

An Asset without an Asset Distribution
Even before an Asset is finalized, a description of what it will be can often be made; for example, a description of it can be written, the publisher is already known as is the language. A link to the distribution, the physical document, can only be made when the work is done; until that time, the Asset will have no Distribution associated with it.
An Asset and Asset Distribution embedded in a single file
Some Assets, such as technical specifications, have some characteristics that are related to the intellectual content such as its description, its language and its version, and some characteristics that are related to the file itself such as its location (if its identifier is not a URL), its format and the usage conditions. In such cases, a single entity is both an Asset and an Asset Distribution. Even so, best practice is to assert the Asset → Asset Distribution relationship (i.e. to point to itself) so that queries looking for that relationship will still return a result.
An Asset with multiple Asset Distributions
It is common for a single work to be expressed in multiple formats. For example, RDF documents are often serialized in RDF/XML, Turtle and triples, each of which would be a discrete Distribution.

5.2 The Secondary Concepts

In addition to the primary concepts, ADMS includes a number of secondary or supporting concepts:

5.2.1 Asset Type

The classification of an Asset according to a controlled vocabulary, e.g. code list, metadata schema. Use dcterms:type to link an Asset to an Asset Type.

5.2.2 Contact Information

A contact point for further information about an Asset. Use dcat:contactPoint to link an Asset to a VCard.

5.2.3 Documentation

Any document that further describes an Asset or gives guidelines for its use. See dcat:landingPage, wdrs:describedby and foaf:page.

5.2.4 File Format

The technical format in which a Distribution is available, e.g. PDF , XSD etc. See also representation technique , dcterms:format and dcat:mediaType .

5.2.5 Geographical Coverage

The country or region to which an Asset or Repository applies, linked using dcterms:spatial .

5.2.6 Identifier

This is based on the UN/CEFACT Identifier class. [ UNCEFACT ]) which consists of:

  • a content string which is the identifier;
  • an optional identifier for the identifier scheme;
  • an optional identifier for the version of the identifier scheme;
  • an optional identifier for the agency that manages the identifier scheme.

In ADMS this is expressed using the adms:Identifier class with the following properties:

  • the content string should be provided using skos:notation , datatyped with the identifier scheme (including the version number if appropriate);
  • use dcterms:creator to link to a class that represents the agency that manages the identifier scheme and/or adms:schemaAgency to provide the name of the agency as a literal;
  • it may also be useful to provide further properties such as dcterms:issued to provide the date on which the identifier was issued.

An important point to note is that properties of adms:Identifier are properties of the Identifier, not the resource that it identifies or the agency that issued it.

5.2.7 Interoperability Level

The interoperability level (e.g. legal, organizational, political etc.) of the Asset, linked using adms:interoperabilityLevel . The interoperability level may be taken from a list of levels such as that of the European Interoperability Framework [ EIF2 ].

5.2.8 Language

The language of an Asset if it contains textual information, e.g. the language of the terms in a controlled vocabulary or the language in which a specification is written, linked using dcterms:language

5.2.9 License

The conditions or restrictions that apply to the use of a Distribution, e.g. whether it is in the public domain, or that some restrictions apply such as attribution being required, or that it can only be used for non-commercial purposes etc. Linked using dcterms:license

5.2.10 Period of time

The time period relevant for an Asset, e.g. for its validity. Linked from a Semanmtic Asset using dcterms:temporal . The time period can be specified using schema:startDate and schema:endDate .

5.2.11 Publisher

The organization making a Repository, Asset or Distribution available, linked using dcterms:publisher .

5.2.12 Representation Technique

The machine-readable language in which a Distribution is expressed. This is more fine-grained than file format , for example "Word 2003", linked using representationTechnique . See also dcterms:format and dcat:mediaType .

This concept indicates that one of the files in an Asset Distribution is expressed in the Representation Technique. There may also be other files in the Distribution that are expressed in other Representation Techniques or even files that are not representations at all.

5.2.13 Status

An indication of the maturity of an Asset or Distribution, linked using adms:status .

5.2.14 Theme

The sector that an Asset applies to, e.g. "law" or "environment". Best practice is to use terms from a controlled vocabulary expressed as a SKOS Concept Scheme and linked from the Asset using dcat:theme .

5.2.15 Theme Taxonomy

A controlled vocabulary that contains terms that are used as Themes for the Assets in a Repository, linked from the Repository using dcat:themeTaxonomy .

NB The original ADMS specification supports the provision of a description of the metadata about an Asset, including its publisher and language (i.e. the human language in which the metadata is expressed, irrespective of the language used in the Asset itself). The DCAT concept of a Catalog Record can be used for this purpose and so is not detailed in this document.

5.3 Properties and Relationships

In the following sub-sections, we set out the properties and relationships (object type properties) used in ADMS. These are listed in alphabetical order, irrespective of namespace.

5.3.1 dcat:accessURL

Any kind of URL that gives access to an Asset Repository or Asset Distribution, e.g. a landing page, download, feed URL, SPARQL endpoint etc. Use dcat:accessURL when you do not have information on which it is or when it is definitely not a download.

Object Type Property dcat:accessURL
Range rdfs:Resource
Usage note
  • the value is a URL.
  • If the distribution(s) are accessible only through a landing page (i.e. direct download URLs are not known), then the landing page link should be duplicated as accessURL on a distribution (see also dcat:landingPage ).

5.3.2 skos:altLabel

An alternative name for the Asset.

Datatype Property skos:altLabel
Range rdfs:Literal

5.3.3 dcat:contactPoint

Links an asset to a contact point from where further information about an Asset can be obtained.

Object Type Property dcat:contactPoint
Range v:VCard

5.3.4 dcterms:creator

Used in ADMS to link an adms:Identifier to a dcterms:Agent (equivalent class foaf:Agent )

Object Type Property dcterms:creator
Range dcterms:Agent

5.3.5 dcat:dataset

Used to link an Asset Repository to an Asset.

Object Type Property dcat:dataset
Domain dcat:Catalog
Range dcat:Dataset

5.3.6 wdrs:describedby

The main documentation or specification of the Asset

Object Type Property wdrs:describedby
Range rdfs:Resource
Usage note See also dcat:landingPage , foaf:page

5.3.7 dcterms:description

A description of the Asset, Asset Repository or Asset Distribution.

Datatype Property dcterms:description
Range rdfs:Literal

5.3.8 dcat:distribution

Links an Asset to an implementation in a particular format.

Object Type Property dcat:distribution
Domain dcat:Dataset
Range dcat:Distribution

5.3.9 dcat:downloadURL

This is a direct link from an Asset Distribution to a downloadable file in a given format, e.g. CSV file or RDF file. The format is described by the distribution's dcterms:format and/or dcat:mediaType.

Object Type Property dcat:downloadURL
Range rdfs:Resource .

5.3.10 schema:endDate

Used in ADMS to define the end of a period of time during which an Asset is valid or applicable.

Datat Type Property schema:endDate
Range rdfs:Literal which should be typed, typically with xsd:date .

5.3.11 dcterms:format

The file format of the distribution.

Object Type Property dcterms:format
Range dcterms:MediaTypeOrExtent
Usage note dcat:mediaType should be used if the type of the distribution is defined by IANA . Suitable values for dcterms:format include URIs as used in the example . See also adms:representationTechnique .

5.3.12 adms:identifier

Links a resource to an adms:Identifier class.

Object Type Property adms:identifier
Range adms:Identifier

5.3.13 adms:includedAsset

An Asset that is contained in the Asset being described, e.g. when there are several vocabularies defined in a single document.

Object Type Property adms:includedAsset
Domain adms:Asset
Range adms:Asset

5.3.14 adms:interoperabilityLevel

The interoperability level for which the Asset is relevant.

Object Type Property adms:interoperabilityLevel
Domain adms:Asset
Range skos:Concept

5.3.15 dcterms:issued

Date of formal issuance (e.g., publication) of the Asset, Asset Repository or Asset Distribution.

Datatype Property dcterms:issued
Range rdfs:Literal using the relevant ISO 8601 Date and Time compliant string and typed using the appropriate XML Schema datatype [ XMLSCHEMA-2 ]

5.3.16 dcat:keyword

A word, phrase or tag to describe the Asset.

Datatype Property dcat:keyword
Range rdfs:Literal

5.3.17 dcat:landingPage

A Web page that can be navigated to in a Web browser to gain access to the Asset, its distributions and/or additional information.

Object Type Property dcat:landingPage
Range foaf:Document
Usage note If the Asset Distribution(s) are accessible only through a landing page (i.e. direct download URLs are not known), then the landing page link should be duplicated as accessURL on a distribution.

5.3.18 dcterms:language

The language of the Asset

Object Type Property dcterms:LinguisticSystem
Range rdfs:Resource
Resources defined by the Library of Congress ( 1 , 2 ) should be used.
If an ISO 639-1 (two-letter) code is defined for language, then its corresponding IRI should be used; if no ISO 639-1 code is defined, then IRI corresponding to the ISO 639-2 (three-letter) code should be used.

5.3.19 adms:last

A link to the current or latest version of the Asset.

Object Type Property adms:last
Sub property of xhv:last
Range rdfs:Resource

5.3.20 dcterms:license

Links to the conditions or restrictions for (re-)use of the Asset Distribution.

Object Type Property dcterms:license
Range dcterms:LicenseDocument .
Usage note If multiple licenses are given, these licenses apply to all files in the Asset Distribution.

5.3.21 dcat:mediaType

The media type of the distribution as defined by IANA .

Object Type Property dcat:mediaType
Range dcterms:MediaTypeOrExtent .
Usage note This property should be used when the media type of the distribution is defined in IANA , e.g. text/csv otherwise dcterms:format may be used with different values. See also adms:representationTechnique .

5.3.22 dcterms:modified

Date of the latest update of the Asset, Asset Repository or Asset Distribution.

Datatype Property dcterms:modified
Range rdfs:Literal using the relevant ISO 8601 Date and Time compliant string and typed using the appropriate XML Schema datatype [ XMLSCHEMA-2 ]

5.3.23 adms:next

A link to the next version of the Asset.

Object Type Property adms:next
Sub property of xhv:next
Range rdfs:Resource

5.3.24 skos:notation

Used in ADMS to provide the actual identifier string as a property of an adms:Identifier

Data Type Property skos:notation
Range rdfs:Literal which should be typed.

5.3.25 adms:prev

A link to the previous version of the Asset.

Object Type Property adms:prev
Sub property of xhv:prev
Range rdfs:Resource

5.3.26 dcterms:publisher

Links an Asset, Asset Repository or Asset Distribution to the publishing foaf:Agent.

Object Type Property dcterms:publisher
Range foaf:Agent

5.3.27 foaf:page

Links to documentation that contains information related to the Asset.

Object Type Property foaf:page
Range foaf:Document
Usage note See also dcat:landingPage , wdrs:describedby

5.3.28 dcterms:relation

A link between two Assets that are related in some (unspecified) way.

Object Type Property dcterms:relation
Range rdfs:Resource

5.3.29 adms:representationTechnique

More information about the format in which an Asset Distribution is released. This is different from the file format as, for example, a ZIP file (file format) could contain an XML schema (representation technique).

Object Type Property adms:representationTechnique
Range skos:Concept
Usage note See also dcterms:format and dcat:mediaType .

5.3.30 adms:sample

Links to a sample of an Asset (which is itself an Asset).

Object Type Property adms:sample
Range adms:Asset

5.3.31 adms:schemaAgency

The name of the agency that issued the identifier.

Data Type Property adms:schemaAgency
Domain adms:Identifier
Range rdfs:Literal

5.3.32 dcterms:spatial

The geographic region to which the Asset or Asset Repository applies.

Object Type Property dcterms:spatial
Range dcterms:Location

5.3.33 schema:startDate

Used in ADMS to define the start of a period of time during which an Asset is valid or applicable.

Datat Type Property schema:startDate
Range rdfs:Literal which should be typed, typically with xsd:date .

5.3.34 adms:status

The status of the Asset in the context of a particular workflow process.

Object Type Property adms:status
Range skos:Concept

5.3.35 adms:supportedSchema

A schema according to which the Asset Repository can provide data about its content, e.g. ADMS.

Datatype Property adms:supportedSchema
Range adms:Asset

5.3.36 dcterms:temporal

The time period to which the Asset applies, e.g. its validity.

Object Type Property dcterms:temporal
Range dcterms:PeriodOfTime

5.3.37 dcat:theme

The theme or sector to which the Asset applies.

Object Type Property dcat:theme
Sub property of dcterms:subject
Range skos:Concept

5.3.38 dcat:themeTaxonomy

The SKOS Concept Scheme used to classify an Asset Repository's assets.

Object Type Property dcat:themeTaxonomy
Range skos:ConceptScheme

5.3.39 dcterms:title

A name given to the Asset, Asset Repository or Asset Distribution.

Datatype Property dcterms:title
Range rdfs:Literal

5.3.40 adms:translation

Links Assets that are translations of each other.

Object Type Property adms:translation
Range rdfs:Resource

5.3.41 dcterms:type

This property is used to point to the specific type of publisher, Asset and License Document. In each case the type should be provided using a controlled vocabulary encoded as a SKOS Concept.

Object Type Property dcterms:type
Range Formally rdfs:Resource but skos:Concept should be used.

5.3.42 owl:versionInfo

A version number or other designation of the Asset.

Annotation Property owl:versionInfo
Range rdfs:Literal

5.3.43 adms:versionNotes

A description of changes between this version and the previous version of the Asset.

Datatype Property adms:versionNotes
Range rdfs:Literal

A. Acknowledgements

ADMS was first developed by and published by the European Commission ISA Programme. Contributors included representatives of Member States of the European Union, operators of national repositories, standardization bodies and independent experts whose work was published in April 2012 [ADMS1]. That document includes the history and motivation behind the development of ADMS, as well as the business need and usage scenario for it.

Further development and review has been undertaken by the Government Linked Data Working Group (GLD WG). This version of ADMS builds on the original work in a broader, global context. It also includes some changes to the original version made as a result of implementation experience, particularly on the European Commission's Joinup Platform.

B. References

B.1 Normative references

Dublin Core metadata initiative. Dublin Core metadata element set, version 1.1. July 1999. Dublin Core recommendation. URL: http://dublincore.org/documents/dcmi-terms/
Data Catalog Vocabulary (DCAT) F. Maali, J. Erickson, P. Archer, W3C Recommendations Track URL: http://www.w3.org/TR/vocab-dcat/
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Internet RFC 2119. URL: http://www.ietf.org/rfc/rfc2119.txt
Paul V. Biron; Ashok Malhotra. XML Schema Part 2: Datatypes Second Edition. 28 October 2004. W3C Recommendation. URL: http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/

B.2 Informative references

ADMS 1.0 European Commission ADMS (link is to a page offering various downloadable files in a variety of formats). URL: http://joinup.ec.europa.eu/asset/adms/release/100
Media Types Application Ed Summers' work on providing URIs for media types URL: http://mediatypes.appspot.com/
European Interoperability Framework (EIF) for European public services (PDF) European Commission. URL: http://ec.europa.eu/isa/documents/isa_annex_ii_eif_en.pdf.
Functional Requirements for Bibliographic Records OFLA 1998 URL: http://archive.ifla.org/VII/s13/frbr/frbr_current_toc.htm
Towards Open Government Metadata (PDF) European Commission Joinup e-Library. URL: http://joinup.ec.europa.eu/sites/default/files/towards_open_government_metadata_0.pdf
(PDF) Core Components Data Type Catalogue Version 3.1 UNECE United Nations Economic Commission for Europe. UN Centre for Trade Facilitation and Electronic Business (UN/CEFACT). URL: http://www.unece.org/fileadmin/DAM/cefact/codesfortrade/CCTS/CCTS-DTCatalogueVersion3p1.pdf