Basic Principles for Managing an RDF Vocabulary

This version:


This document articulates some basic principles of good
practice for managing an RDF vocabulary.   Following these
principles makes an RDF vocabulary "usable": new users
learn quickly how to use the vocabulary, and a relationship
of trust is built between the user community and the
vocabulary developers/maintainers.  This promotes growth
of a user community, which generates more feedback for the
developers/maintainers, leading to further improvements in
quality and usability.

This document focuses on those principles of good practice
where a clear recommendation can be made.  A number of issues
related to the management of RDF vocabularies have yet to
be resolved, but these are outside the scope of
this document.


An RDF vocabulary is a set of resources denoted by URIs.
Informally, these resources are known as the "terms" of the
vocabulary. The resources will usually (but not necessarily) be
of type rdf:Property, rdfs:Class, owl:Class, or skos:Concept.

An RDF vocabulary is created and maintained for the use of a
community of people (the 'user community') as a set of building
blocks for creating RDF descriptions of things in their domain
of interest.  An RDF vocabulary usually implies a shared
conceptualisation, and thus the notion of an 'RDF vocabulary'
is almost identical to the notion of a 'web ontology' [ref???].

Several of the most prominent RDF vocabularies currently in
use (OWL, FOAF, Dublin Core, SKOS Core) have emerged from a
close collaboration between a relatively small community of
developers and a larger community of users.  The prominence
of these vocabularies may be attributed to their utility,
but also to the commitment made by those responsible
for developing/maintaining the vocabularies to forming,
accomodating, serving, and working with, a community of users.

The goal of implementing the principles outlined in this
document is to make an RDF vocabulary "usable".  This could be
restated as, managing an RDF vocabulary in such a way that it 
can easily be understood and deployed by users.

.... [some other stuff ???]  

Principles of Good Practice

1. Name Terms using URI References

An RDF vocabulary consists of a set of resources denoted by URIs.  'Naming'
refers to the act of allocating URIs to resources [ref???].  

The developers/maintainers of an RDF vocabulary should inform the potential user
of the following:

 - The URI space from which resource names are drawn.

 - The ownership of this URI space.

 - Any commitments made by the owner(s) of the URI space to the persistence of
   URIs in that space.

 - Have the owner(s) of the URI space formally delegated responsibility for
   allocating URIs within that space to the vocabulary developers/maintainers?

 - Any rules used by the developers/maintainers for constructing URIs to be used
   as resource names.

E.g.s ....

2. Provide readable documentation

The developers/maintainers of an RDF vocabulary should provide natural-language
(i.e. human-readable) documentation about the vocabulary and its proper use.
The principle aim of this documentation is to help potential users *learn* how
to apply the vocabulary, and therefore to promote *consistency* in the way that
the vocabulary is applied.  Inconsistent usage reduces the value of a
vocabulary, because the meaning associated with the vocabulary becomes in
practice ambiguous.

As a bare minimum, a list of the terms should be published, with text
definitions.  It is recommended to publish detailed prose describing proper
usage patterns and scenarios, with examples.


3. Articulate your Maintenance Policies

An RDF vocabulary may be developed in private by a closed community, and then
published with no possibility for future change.  An RDF vocabulary may, on the
other hand, be developed in public by an open community, with the content of the
vocabulary being allowed to evolve indefinitely.  In any case, a potential user
needs to know under what circumstances the vocabulary (or parts of it) may
change, and what kinds of change may be expected.  

The key concept here is 'stability'.  When a potential user chooses a
vocabulary, they are making an investment of time/money/effort that depends to a
certain extent upon the stability of that vocabulary.  Therefore a potential
user needs to know exactly how stable a vocabulary is, in order to judge how
much to invest.  If a vocabulary is less than perfectly stable, the user needs
to know exactly what may change, how it may change, and of course to be informed
of changes when they do occur.

Therefore, the developers/maintainers of an RDF vocabulary should publish a
maintenance policy for that vocabulary.  The maintenance policy should
articulate whether or not change is allowed, and the way that change is managed.


The developers/maintainers should also provide some facility whereby users can
be informed of changes as and when they are made.


4. Identify Versions

Where a vocabulary is allowed to change, users developing systems based on that
vocabulary may prefer to work to a stationary, rather than moving, target.  To
support these users, the developers/maintainers of a vocabulary should:

 - Publish versions of the vocabulary, where a 'version' is a 'snapshot' of the
   vocabulary at a particular point in time.  

 - Allocated URIs to vocabulary versions, so that they may be referred to.

Where the resources that are the members of a vocabulary may evolve
independently, or be at differing levels of stability, the
developers/maintainers may also which to allocate URIs to historical versions of
a particular resource.


5. Publish a Formal Schema

An RDF description of an RDF vocabulary should be published.  Potential users
should be clearly informed as to which is the 'authoritative' RDF description of
an RDF vocabulary.

Where the resources that are the members of an RDF vocabulary are denoted by
HTTP URIs, an HTTP GET request with the header field
'accept=application/rdf+xml' against that URI should return an RDF/XML
serialisation of an RDF graph that includes a description of the denoted