- From: Thomas Baker <thomas.baker@izb.fraunhofer.de>
- Date: Wed, 27 Oct 2004 15:51:43 +0200
- To: SW Best Practices <public-swbp-wg@w3.org>
SWBPD "Vocabulary Management"
Draft, 2004-10-27
Abstract
Metadata element sets, taxonomies, subject headings,
thesauri, and ontologies are examples of vocabularies which
are increasingly used in a "Semantic Web" environment.
Managing vocabularies for use in Semantic Web applications
means identifying, documenting, and publishing vocabulary
terms in ways that facilitate their citation and re-use in a
wide range of applications. This paper examines practices in
the maintenance communities for representative vocabularies
ranging from small and informal to large and complex.
The paper formulates principles of good practice and summarizes
discussion on issues for which good practice has yet to emerge.
1. Introduction
1.1. Vocabularies in the Semantic Web
The Semantic Web is an open, distributed, loosely-coupled
environment with lots of languages (metadata element
sets, controlled vocabularies, taxonomies, thesauri,
ontologies, etc). Organizations or even individuals can
define and publish vocabulary terms in an open, bottom-up,
and distributed manner. This paper is addressed to people
who want to create and maintain such a Vocabulary.
This paper articulates some basic principles for doing
so in a Semantic-Web-friendly way. By this we mean
vocabularies that can support processes of referencing,
repurposing, recombining, or merging data from a diversity
of sources; that are evolvable; that are extensible and
mixable with other Semantic Web vocabularies; and that
are declared in a way that is processable by networked
machines in an emerging "semantic infrastructure".
[Bernard asks: Which processes are the terms supposed to
support -- indexing, vocabulary merging, data integration,
search...? Do we say something about those processes or
are we agnostic?]
TASK: James - One page on "vocabularies in Semantic Web"
The two placeholder paragraphs above should be expanded
into one short page providing a general introduction
to the topic "vocabularies in the Semantic Web" --
what kinds of vocabularies are we talking about here
(e.g., the typology in [PIDCOCK]) and what does it mean
to use them in a "Semantic Web" environment? Rather
than elaborate very much in-line, this section should
point off to further reading about Semantic Web.
1.2. Method of this paper
In Section 2, this paper will formulate a few principles
of good practice applicable to Semantic Web vocabularies
in general. To illustrate these principles, the paper
will describe practices used in several vocabularies
chosen to exemplify a range from small and informal to
large and complex:
-- FOAF
TASK: DanBri and Libby - One paragraph on FOAF
FOAF serves as an example of a "relatively small"
vocabulary for "descriptive metadata" about people
and their interests [FOAF]. Its maintenance
processes are "somewhat informal".
-- Dublin Core
TASK: Tom - One paragraph about Dublin Core
Dublin Core serves as an example of a "medium-sized"
vocabulary for "descriptive metadata" about
information resources [DC]. Its maintenance
processes are "lightweight but not weightless"
and increasingly formal as DCMI evolves from a
workshop-driven movement to a stable maintenance
community supported by institutional stakeholders.
-- SKOS
TASK: Alistair - One paragraph about SKOS
SKOS serves as an example of a "medium-sized"
vocabulary for describing "thesauri" and similar
types of knowledge organization systems. (Not sure
about maintenance issues.) The SWBPD thesaurus
activity should be cited.
-- Princeton Wordnet
TASK: Aldo - One paragraph about wordnet issues
As a lexical system of synonym sets for the English
language, Princeton Wordnet can serve as an example
of a "large-scale" vocabulary. (Not sure about
maintenance issues.) The SWBPD activity should
be cited [SWBP-WNET].
-- A major medical or life-sciences vocabulary?
TASK: Alan or Natasha - An example of a large-scale ontology?
Do we perhaps need another major example? It would
be good to have a "large-scale" vocabulary of the
"ontology" sort, preferably with some well-defined
maintenance and versioning policies...
In addition, this paper cites several prior works on
good practice in closely related areas:
-- World Wide Web Architecture and Semantic Web principles
TASK: DanBri - Bullet point on W3C good-practice documents
TBL has written about Web architecture, and TAG
has come out with Architecture of the World
Wide Web, First Edition [SW-ARCHITECTURE and
W3C-TAGARCHITECTURE]. A bullet point should put
these various formal and informal position papers
into the proper perspective for outsiders to W3C.
-- OASIS Published Subjects
TASK: Bernard - Bullet point on OASIS Published Subjects
The bullet point should provide some context on Topic
Maps and Semantic Web and on the PSI Recommendation
[OASIS-PUBSUBJ].
The terminology used to talk about vocabularies and
their underlying linguistic models differ between
user communities. Without wishing to imply that these
differences are trivial, this paper uses a small set of
words defined with deliberate fuzziness:
Term A named concept.
Vocabulary A set of terms.
URI Reference A globally unique identifier.
Description A set of statements about a term or vocabulary.
Declaration A machine-processable representation of
a term or vocabulary.
Vocabulary Owner The maintainer of a term set.
Versioning The identification of changes to a term
or vocabulary.
These words are qualified in the examples which follow
and in the Glossary. One potential source of confusion
should perhaps be acknowledged and discussed up-front:
the term "namespace", which is used in a number of
vocabulary communities, W3C in particular, but is (in my
opinion) difficult to pin down. If we can agree to use
"vocabulary" in this paper (noting the usage of "namespace"
where appropriate), I would like to task someone (DanBri?)
to explain the W3C use of the term "namespace".
TASK: DanBri or Libby - Describe W3C usage of the word "namespace"
2. Principles of Good Practice
Short paragraph explaining that in this section, we formulate
and illustrate principles of good practice on which we
generally agree.
2.1. Identify Terms with URI References.
TASK: DanBri - Define "URI Reference", elaborating in the Glossary
TASK: DanBri - Sentence or two on FOAF term URIrefs
TASK: Tom - Sentence or two on DCMI term URIrefs
TASK: Tom - A sentence on the "CORES Resolution"
TASK: Alistair - Sentence or two on SKOS term URIrefs
TASK: Aldo - Sentence or two on Wordnet term URIrefs
TASK: DanBri - What W3C says about identifying terms
TASK: Bernard - What PSI says about identifying terms
2.2. Articulate and publish maintenance policies for the Terms
and their URI references.
A Vocabulary Owner should specify and publish any policies
governing the maintenance of the terms and their URI
references: e.g. institutional commitments to persistence
and semantic stability. This short to medium-length
section should simply describe a sample of such policies.
[It would be nice if we could agree on something of
the substance of those policies, such as stability of
URI references in the face of "semantically compatible"
evolution, but this may be difficult to define.]
TASK: DanBri - Describe maintenance policies for FOAF
TASK: Tom - Describe maintenance policies for DCMI
TASK: Alistair - Describe maintenance policies for SKOS
TASK: Aldo - Describe maintenance policies for Wordnet
TASK: DanBri - What W3C says about maintenance policies
TASK: Bernard - What PSI says about maintenance policies
TASK: Alistair - TAG Versioning on "semantic stability"
2.3. Identify the historical version of a Vocabulary or
its Terms.
Building on the previous section, this section should
look at versioning from the standpoint of identification.
At what level of granularity does versioning operate? Are
URI references being assigned to individual terms,
to sets of terms in the abstract, or to documents or
schemas of term sets? Presumably, this section should
highlight W3C practice in this area (e.g., the method
of distinguishing a timeless Latest Version from a
date-stamped This Version and Previous Version).
TASK: Ralph - Longer paragraph on versioning in W3C
TASK: DanBri - Short paragraph on versioning in FOAF
TASK: Tom - Short paragraph on versioning in DCMI
TASK: Alistair - Short paragraph on versioning in SKOS
TASK: Aldo - Short paragraph on versioning in Wordnet
TASK: Bernard - Short paragraph on versioning in PSI
TASK: Alistair - What TAG says about versioning
TASK: Alan - "What constitutes a change?"
2.4. Provide documentation about the Terms.
The Vocabulary Owner should describe and publish a
human-readable description of the Terms -- typically,
at a minimum, text definitions on a Web page. This short
section should merely say what sort of Web documents are
made available for the example vocabularies.
TASK: DanBri - One sentence pointing to FOAF Web documents
TASK: Tom - One sentence pointing to DCMI Web documents
TASK: Alistair - One sentence pointing to SKOS Web documents
TASK: Aldo - One sentence pointing to Wordnet Web documents
TASK: DanBri - One sentence pointing to W3C Web documents
TASK: Bernard - One sentence pointing to PSI Web documents
2.5. Declare the Terms using a machine-processable schema
language.
This short section should merely say what sorts of
schemas the example maintenance communities publish.
Policies for dereferencing and choice of schema language
will be discussed in more detail in Section 3.
TASK: DanBri - Two sentences on FOAF schemas.
TASK: Tom - Two sentences on DCMI schemas.
TASK: Alistair - Two sentences on SKOS schemas.
TASK: Aldo - Two sentences on Wordnet schemas.
TASK: DanBri - Two sentences on W3C schemas.
TASK: Bernard - Two sentences on PSI schemas.
3. Questions on the Bleeding Edge
Paragraph explaining that Section 3 discusses issues on
which consensus currently seems more elusive. Our goal is
to describe the range of positions taken.
3.1. What should the identifier of a Vocabulary or Term (i.e.,
its URI Reference) resolve to when someone "clicks on it"
in a Web browser?
We could reword this as the problem of resolving
("dereferencing") Term URIs to human-readable descriptions
or machine-processable declarations. Several years ago,
Tim Berners-Lee said that "The namespace document (with
the namespace URI) is a place for the language publisher
to keep definitive material about a namespace. Schema
languages are ideal for this." Others have disagreed with
this and the question was taken up by TAG. Point 3.1
should summarize the state of discussion. If Terms are
documented in multiple ways, should a Vocabulary Owner
distinguish between "canonical" versus "derived" sources?
TASK: Ralph - Paragraph or two on W3C dereferencing policy
TASK: Bernard - Paragraph on PSI dereferencing policy
TASK: DanBri - Short paragraph on FOAF dereferencing policy
TASK: Tom - Short paragraph on DCMI dereferencing policy
TASK: Alistair - Short paragraph on SKOS dereferencing policy
TASK: Aldo - Short paragraph on Wordnet dereferencing policy
3.2. Which schema language should be used to declare the
Vocabulary machine-processably?
Short answer: It depends what you want to say.
This section should characterize the assertions made
in schemas published by various communities.
TASK: DanBri - Short paragraph on what FOAF schemas assert.
TASK: Tom - Short paragraph on what DCMI schemas assert.
TASK: Aldo - Short paragraph on what Wordnet schemas assert.
TASK: DanBri - Short paragraph on what W3C schemas assert.
TASK: Bernard - Short paragraph on what PSI schemas assert.
TASK: Alistair - Short paragraph on what SKOS schemas assert.
In particular, there was a discussion in September on
the SWBPD list on different approaches to modeling
thesauri [THESAURUS-MODEL]. For example, one could
use OWL or RDFS to represent an existing language of
thesaurus relations and simply translate an existing
thesaurus into those terms. Or one could fundamentally
remodel the thesaurus using native OWL constructs --
a much more ambitious task (because the semantics of
class, subclass, etc, are not identical to thesaurus
terms). When is it "good enough" to express the fuzzy
semantics of an existing thesaurus, which can be done
rather automatically, and what does the extra effort of
remodeling an ontology buy for applications? There is
an overlap here with the PORT task force.
TASK: Alistair - Discuss alternative ways to model a thesaurus
3.3. What does it mean to "use" Terms from one Vocabulary
in another?
This issue has at least two aspects:
-- The problem of "semantic context". Terms may be
embedded in clusters of relations from which they
may be seen in part to derive their meaning. It may
therefore not always be sensible to use those terms out
of context. Examples include the terms of thesauri
or ontologies, as well as XML elements, which may
be defined with respect to parent elements and may
therefore not always be reusable as properties in an
RDF sense without violating their semantic intent.
TASK: Bernard - Reuse of existing terms in a local context
TASK: Tom - DCMI on "terms usable as RDF properties"
TASK: Everyone - Using terms outside of their original contexts
-- Application profiles. Many (most?) vocabulary
maintainers end up with some notion of "profile" to
designate either a constrained subset of the vocabulary
and/or a language which mixes multiple vocabularies
for a particular purpose or application. The VM note
could characterize the nature of these constructs.
TASK: Tom - Describe the DCMI notion of "application profile"
TASK: Everyone - Describe other notions of "application profile"
3.4. What does it mean to "own" a Vocabulary?
In this section, we acknowledge that "vocabularies"
are inherently a human linguistic phenomenon. As with
other forms of language, there is inevitably a tension
between the meaning intended by a speaker and meaning
as interpreted or imposed by others.
If this paper is addressed to vocabulary maintainers
(existing and potential) -- and we have in essence
articulated some responsibilities for vocabulary
maintainers (in Section 2 above) -- we should also
question our underlying assumptions. The RDF Concepts and
Abstract Syntax draft of 2003-01-23 said that "The social
conventions surrounding use of RDF assume that any RDF URI
reference gains its meaning from some defining individual,
organization or context... For important documents, the
use of third-party vocabulary should be restricted to
terms defined by trustworthy parties (e.g. recognized
standards bodies or reputable organizations)...".
In response to that draft, however, there was animated
discussion about the "social meaning" versus the "formal
meaning" of RDF assertions [SW-MEANING]. This debate
should perhaps be summarized from the standpoint of a
Vocabulary maintainer.
TASK: Jeremy? - Summarize discussion of "social meaning"
Even if we acknowledge the notion of "ownership" to be
problematic, we should perhaps introduce the notion
of "trust". Tom could briefly describe negotiations
between the DCMI Usage Board with the Library of
Congress whereby LoC asserts certain MARC Relator terms
(identified with URI references) to be sub-properties
of dc:contributor, and DCMI endorses those assertions
("assertion etiquette"?).
TASK: Tom - DCMI endorsing assertions about MARC Relator terms
TASK: Everyone - Comment on the role of the "vocabulary owner"
3.5. When a term is needed, when should one adapt
an existing term, declare a new one, or get an established
vocabulary maintainer to host it?
It would be good to end the VM note with this question,
because I suspect that alot of the readers will be asking
precisely this question. This is where we can summarize
our understanding of good practice for maintenance and
persistence policy. Andy Powell's sensible advice on
these issues could be summarized here [DC-IDENTIFIERS],
along with a general characterization of the "vocabulary
market" [VOCABULARY-MARKET]. We could introduce the
notion of a Vocabulary Host, and Tom would be happy
to describe discussion about this within DCMI from the
standpoint of long-term maintenance responsibility and
related institutional models. Given that one option is
to coin a URI references, we should at least characterize
choices with regard to forming the identifier strings:
"hash or slash" and the implied semantics of words,
version numbers, or directory hierarchies embedded in
URI strings.
TASK: DanBri or Libby - Describe the "vocabulary market"
TASK: DanBri or Libby - Formation of URI strings ("hash or slash" etc)
TASK: Tom - DCMI guidelines on coining URI references
TASK: Tom - DCMI perspective on "namespace hosting"
TASK: Everyone - When and how to declare new or reuse existing terms
Glossary
This section -- if we need it -- can provide annotations
for our minimal terminology from the standpoint of other
vocabulary maintenance communities. From the standpoint of
Dublin Core, for example, one might note here that "term"
corresponds to what DCMI calls an Element or Element
Refinement (aka Property), or an Encoding Scheme, etc.
Alan could point out how this use of "term" differs
from "term" in the medical community (as distinct from
"concept").
-- Term: a named concept.
-- Vocabulary: a set of terms.
-- URI Reference: a globally unique identifier.
-- Description: a set of statements about a term or vocabulary.
-- Declaration: a machine-processable representation of
a term or vocabulary
-- Vocabulary Owner: the maintainer of a term set.
-- Versioning: the identification of changes to a term
or vocabulary.
TASK: DanBri or Libby - Define URI Reference
According to my notes, the "RFC2396bis redraft
will, in the Appendix, clearly state why we say
URIref not just URI" [RFC2396bis].
TASK: DanBri - Annotate Glossary with FOAF usage where appropriate
TASK: Tom - Annotate Glossary with DCMI usage where appropriate
TASK: Alistair - Annotate Glossary with SKOS usage where appropriate
TASK: Aldo - Annotate Glossary with Wordnet usage where appropriate
TASK: Ralph - Annotate Glossary with W3C usage where appropriate
TASK: Bernard - Annotate Glossary with PSI usage where appropriate
References
[I have started to fill out the references. The names next
to many of the references are my best guess as to who should
cover a particular resource in the context of the paper.
Note several related articles or resources are sometimes
grouped under one heading - please help decide which of them
is most salient for the purposes of citation. Please also
let me know if any of the following are no longer needed, and
feel free to help fill in any missing citation information.]
[CORES-RESOLUTION] - Tom
CORES Resolution on Metadata Element Identifiers,
http://www.dlib.org/dlib/july03/baker/07baker.html.
[DC] - Tom
http://dublincore.org/documents/dcmi-terms/
http://dublincore.org/
[DC-IDENTIFIERS] - Tom
Powell, A., Guidelines for assigning identifiers to metadata terms,
[draft], http://www.ukoln.ac.uk/metadata/dcmi/term-identifier-guidelines/.
[DC-NAMESPACE] - Tom
DCMI Namespace Policy,
http://dublincore.org/documents/dcmi-namespace/
[DC-PROFILES] - Tom
Dublin Core Application Profiles, http://www.cenorm.be/isss/cwa14855/.
[FOAF] - DanBri and Libby
http://xmlns.com/foaf/0.1/
http://www.w3.org/2001/sw/Europe/events/foaf-galway/
http://rdfweb.org/topic/FoafGalway
FOAF Community Process, http://rdfweb.org/topic/FOAFCommunityProcess.
[OASIS-PUBSUBJ] - Bernard
Pepper, S., ed., Public Subjects: Introduction
and Basic Requirements, OASIS Published Subjects
Technical Committee Recommendation, 2003-06-24,
http://www.oasis-open.org/committees/download.php/3050/pubsubj-pt1-1.02-cs.pdf.
http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=tm-pubsubj
http://www.oasis-open.org/committees/tm-pubsubj/docs/recommendations/issues.htm
Also: OASIS (ISO/TS 15000) ebXMLRegistry Semantic Content.
[PIDCOCK]
Pidcock, W., Relationships between Metamodels, Ontologies,
Thesauri, Taxonomies and Controlled Vocabularies,
http://www.metamodel.com/article.php?story=20030115211223271
Comments by Mike Uschold:
http://www.metamodel.com/article.php?story=20030115211223271#comments
[RDF-PRIMER]
RDF Primer, http://www.w3.org/TR/rdf-primer/.
[RDF-QUERY] - where does this fit?
Libby and Dan work on RDF query,
http://www.ilrt.bris.ac.uk/discovery/2001/06/process/.
[RFC2396bis] - DanBri
http://www.ietf.org/internet-drafts/draft-fielding-uri-rfc2396bis-07.txt
[SKOS] - Alistair
SKOS Core Guide, http://esw.w3.org/topic/SkosCoreGuideToc - SKOS Core Guide
http://www.w3.org/2004/skos/core.rdf
http://www.w3.org/2001/sw/Europe/reports/thes/1.0/guide/
http://www.w3c.rl.ac.uk/2003/11/21-skos-mapping
[SWBP-WNET] - Aldo
Gangemi, A., editor. Porting Wordnets to the Semantic Web,
http://www.w3.org/2001/sw/BestPractices/WNET/Porting.
http://www.cogsci.princeton.edu/%7Ewn/index.shtml
[SWAD-THESAURUS] - Dan, Bernard and Alistair participated
SWAD-E Thesaurus - "standard" thesaurus change management
guidelines are wanted,
http://lists.w3.org/Archives/Public/public-esw-thes/2004Apr/
[SW-ARCHITECTURE] - DanBri or Libby?
Berners-Lee, T. Getting into RDF and Semantic Web using N3,
http://www.w3.org/2000/10/swap/Primer.
Berners-Lee, T. Web Architecture from 50,000 feet, 1999,
http://www.w3.org/DesignIssues/Architecture#Namespaces
[SWBP-THESAURUS] - Dan and Alistair
Semantic Web Best Practices: Thesaurus Task Force,
http://www.w3.org/2004/03/thes-tf/mission
[SW-MEANING] - volunteer needed to summarize!
RDF Core discussion on issues related to social meaning (Jeremy),
http://www.w3.org/TR/2003/WD-rdf-concepts-20030123/#section-Meaning had WG
consensus, then got trashed:
http://lists.w3.org/Archives/Public/www-rdf-comments/2003JanMar/0366
then got revised:
http://lists.w3.org/Archives/Public/www-rdf-comments/2003JanMar/0486
http://www.w3.org/2001/sw/meetings/tech-200303/social-meaning
Mailing list addressing questions of "namespace ownership":
http://lists.w3.org/Archives/Public/public-sw-meaning/2004Jun/
[THESAURUS-MODEL]
VM discussion thread on SWBPD list, e.g.:
http://lists.w3.org/Archives/Public/public-swbp-wg/2004Sep/0035.html
http://lists.w3.org/Archives/Public/public-swbp-wg/2004Sep/0036.html
http://lists.w3.org/Archives/Public/public-swbp-wg/2004Sep/0042.html
[VOCABULARY-MARKET] - DanBri
Vocabulary Market, http://esw.w3.org/topic/VocabularyMarket
Image Annotation meeting in Madrid,
http://rdfig.xmlhack.com/2004/06/07/2004-06-07.html#1086615887.400193
RDFIG Geo vocab workspace, http://www.w3.org/2003/01/geo/.
[W3C-VERSIONING] - Ralph
W3C Publication Rules, http://www.w3.org/2004/02/02-pubrules.html
URIs for W3C Namespaces, http://www.w3.org/1999/10/nsuri
[W3C-TAGARCHITECTURE] - DanBri?
Jacobs, I., Walsh, N., Architecture of the World Wide
Web, First Edition, Technical Architecture Group (TAG),
http://www.w3.org/TR/2004/WD-webarch-20040816/.
[W3C-TAGISSUES] - DanBri or Libby
W3C TAG on "What should a 'namespace document' look like?
http://www.w3.org/2001/tag/issues.html#namespaceDocument-8.
TAG "consensus" on namespace documents,
http://www.w3.org/2003/09/15-tag-summary.html.
Resource Directory Description Language (RDDL), http://www.tbray.org/tag/rddl4.html.
[W3C-TAG-XMLVERSIONING] - Alistair
Orchard, D., Walsh, N., eds. Versioning XML Languages,
Proposed TAG Finding 16 November 2003 [Editorial Draft],
http://www.w3.org/2001/tag/doc/versioning
[WGS84] - DanBri??
Walsh, J. An RDF vocabulary for WGS84 geo positioning
[Informational Internet draft], RDF Interest Group,
http://space.frot.org/draft-geo-draft.html.
--
Dr. Thomas Baker Thomas.Baker@izb.fraunhofer.de
Institutszentrum Schloss Birlinghoven mobile +49-160-9664-2129
Fraunhofer-Gesellschaft work +49-30-8109-9027
53754 Sankt Augustin, Germany fax +49-2241-144-2352
Personal email: thbaker79@alumni.amherst.edu
Received on Wednesday, 27 October 2004 13:46:28 UTC