- From: Antoine Zimmermann <antoine.zimmermann@emse.fr>
- Date: Fri, 5 Jul 2019 12:03:13 +0200
- To: Dan Brickley <danbri@danbri.org>
- Cc: semantic-web <semantic-web@w3.org>
Thanks a million, Dan! I think this answers the question and closes the debate. --AZ Le 02/07/2019 à 16:27, Dan Brickley a écrit : > > > On Fri, 28 Jun 2019 at 09:01, Antoine Zimmermann > <antoine.zimmermann@emse.fr <mailto:antoine.zimmermann@emse.fr>> wrote: > > Recently on Stack Overflow, there was a question asking "Why rdf:Seq > and > not rdfs:Seq?" [1]. I tried to answer the best I could, by digging in > the old RDF mailing lists, but I am still puzzled about how some terms > ended up in the rdf: namespace rather than rdfs: (and vice versa). Can > someone involved in the early days of RDF enlighten us about this? > > Nowadays, the duplication of namespaces for RDF terms seems rather > silly, confusing, and counter productive. Maybe it made sense, back in > the days... > > > Sure, let me fill in some details, possibly too many. This all dates > from 1997. In 1997, several things happened. > > * W3C via its Metadata Activity (https://www.w3.org/Metadata/) led by > Ralph Swick, was getting reorganized. The PICS system for content > labelling was to be generalized. PICS already (from 1995/6) included a > label syntax (https://www.w3.org/PICS/labels-951121.html), signed labels > (https://www.w3.org/TR/2009/REC-DSig-label-20091124/), a rule language > (https://www.w3.org/TR/2009/REC-PICSRules-20091124/) and a "label > bureau" protocol. However it did not provide a way for multiple > independent labelling schemes to be used together, for rich structured > descriptions, and for datatyped (strings, numbers etc.) rather than > categorical rating values. > * June 1997 - Netscape submitted Meta Content Framework (MCF) in XML, > https://www.w3.org/Submission/1997/8/ - both a spec > (https://www.w3.org/TR/NOTE-MCF-XML/) and a tutorial > (https://www.w3.org/TR/NOTE-MCF-XML/MCF-tutorial.html). While MCF is > clearly the technical ancestor to a lot of what you see in RDF, it > didn't have the same partitioning; the MCF spec had model, syntax, > schema and some starter vocabulary. > * The Dublin Core metadata initiative, meanwhile, was trying to express > in-page Web metadata using HTML 3.2's simple "meta" tags, and > encountering difficulties with nested or repeated fields; e.g. see > http://www.dublincore.org/specifications/dublin-core/info-factoring/2001-03-19/ (1996) > http://www.dlib.org/dlib/june97/metadata/06weibel.html . This 1996 AHDS > report gives a feel for the metadata formats of that era, > https://web.archive.org/web/19980118053003/http://ahds.ac.uk/public/metadata/disc_32.html . > For example, if you had multiple authors with multiple sets of contact > details each, you ended up with metadata fields named things like > "DC.creator.email.2". See also http://www.ariadne.ac.uk/issue/7/mcf/ for > Dublin Core community exploration of using MCF. > * Lots of projects were crawling the Web and extracting metadata, e.g. > see the earlier 1996 workshop, > https://www.w3.org/Search/9605-Indexing-Workshop/ and > https://www.w3.org/Search/9605-Indexing-Workshop/ - you'd see mentions > of formats like SOIF from the Harvest indexing project, or MARC and the > Z39.50 protocol from libraries. > * XML itself was taking shape (as a cut down format derrived from SGML), > including a draft namespaces mechanism. > > It was also the height of the browser wars. > > I'm sure I've missed a bunch of stuff, but the picture is basically that > the Web had just broken through into everyday life and things were crazy > and moving fast. So when W3C (itself a very new organization) planned > the RDF work there was a sense that it needed to be partitioned and > layered, and to get something useful out soon without being stuck in > complexity. > > Two RDF Working Groups were initially created in 1997; first (May 1997) > the Model and Syntax WG https://www.w3.org/RDF/Group/Syntax/ (pages are > W3C Members only, still), and a little later that year, the RDF Schema > WG https://www.w3.org/RDF/Group/Schema/ > > Their charters are not public but I think it is reasonable to excerpt here. > > From https://www.w3.org/RDF/Group/SyntaxCharter > > """Purpose and Scope: The Resource Description Framework Model and > Syntax Working Group (RDF-syntax-wg) will define an interchange format > for encoding and exchange of structured resource description data > (metadata) for Web resources. This framework will include all the > capabilities of PICS-1.1 and in addition will support more general > models of resource description, including non-numeric and structured > attribute values. The RDF Model and Syntax WG will work closely with an > RDF Schema WG. > > Requirements > The goal of RDF is to provide a single mechanism for representing > metadata across many applications. The semantics and structure of many > varieties of metadata will be specified by independent communities. The > RDF must provide an infrastructure that is sufficiently general and > flexible to support these disparate applications. Example applications > include sitemaps, content ratings, stream channel definitions, search > engine data collection (web crawling), digital library collections, and > distributed authoring. > > Dependencies > The RDF is an evolutionary step from PICS-1.1. The importance of the > content rating application is recognized explicitly by a requirement > that the RDF support existing PICS-1.1 data types and functional > specifications. It must be possible to automatically translate PICS-1.1 > labels to RDF. > > The RDF Model and Syntax Working Group is responsible for defining an > architecture and interchange format for resource descriptions. The RDF > Schema design is the responsibility of a separate but closely > coordinated working group. > > There has been an agreement that the RDF work will build on top of XML, > and that the XML namespace work will supply some of the modularity > requirements for RDF. > > The Model and Syntax Working Group will also incorporate into the > Resource Description Framework any requirements for the purposes of > digitally signing resource descriptions defined by the W3C Digital > Signature Working Group.""" > > > > The RDF Schema WG's charter followed along a few months later, > > """Purpose and Scope > The Resource Description Framework Schema Working Group (RDF-schema-wg) > will define a model for schemas to specify the semantics of information > encoded in the Resource Description Framework and a language for the > encoding and exchange of those schemas. > > Requirements > This schema model must be consistent with the data model produced by the > RDF Model and Syntax Working Group. While it is recognized that not all > aspects of metadata semantics can be described in a machine > understandable form the goal of the RDF Schema working group is to build > on well understood methods from the fields of database schema > representation and AI knowledge representation to enable this as far as > possible. > > The RDF Schema language must be syntactically compatible with the > language chosen by the RDF Model and Syntax Working Group and must > support all the functions in a PICS-1.1 rating service description. It > must be possible to automatically translate PICS-1.1 rating service > descriptions to RDF schemas. > > The goal of RDF is to provide a single mechanism for representing > metadata across many applications. The semantics and structure of many > varieties of metadata will be specified by independent communities. Much > of these semantics can be specified in a declarative machine > understandable form. Having such specifications available will greatly > improve interoperability. The goal of the RDF Schema mechanism is to > enable this. > > Dependencies > The RDF Schema Working Group will coordinate with the RDF Model and > Syntax Working Group to insure that all the features of the data model > defined by the Model and Syntax Working Group are represented in the RDF > Schema specification. The Metadata Coordination group will help with > this coordination.""" > > --- > > In the two Working Groups, the way this played out was that the RDF M+S > WG introduced certain notions informally and "in passing", without > elaboration, and the RDFS group fleshed out some of those details. > Meanwhile, the RDFS WG took care not to introduce new syntax, and > decided to express its schema language within RDF using whatever syntax > the other Working Group created. The first public draft of RDF was the > M+S spec from October 1997: https://www.w3.org/TR/WD-rdf-syntax-971002/ > > It already talked in MCF-like terms of "In this data model both the > resources being described and the values describing them are nodes in a > directed labeled graph (and values may also be resources). The arcs > connecting pairs of nodes correspond to the names of the property > types." ... and a basic notion of types followed along soon enough too. > The requirement to represent ordered structures within this otherwise > unordered graph data model was identified immediately, and tied in to > the practical requirements that came from PICS and from the various > other metadata efforts of that era that I've sketched. > > The RDF M+S WG put things in their namespace like rdf:type, while trying > to say as little as possible about the nature of namespaces, schemas and > related things. There was also a rough suggestion, sometimes articulated > explicitly, that multiple different schema systems could be built on top > of the base RDF. Or that instance data could stand alone, schema-less, > and still be useful. When DARPA's DAML came along a few years later, the > idea of alternatives to RDFS sharing the same base took more explicit > shape with DAML+OIL and OWL, but there were also some rather tense > discussions with XML groups in the 1997-9 period. XML was grounded in > SGML heritage and there was a broad expectation that the DTD part of > SGML (and XML) would eventually replaced/modernized, and that when this > happened, there would be an opportunity for the relationship between RDF > and XML to be made more explicit. XML people were not super happy at the > prospect of their future schema language being expressed somehow in RDF > (although Tim Bray made a draft exploring this, see > https://www.w3.org/TR/NOTE-dcd). And the RDF/S WGs didn't see a way for > DTDs to really make sense for use with RDF. Nevertheless there were > clear points of overlap, e.g. datatypes. It was clear that 1998-era RDFS > wouldn't be the last word on the topic. You can see some of this > baggage in earlier drafts of RDFS e.g. > https://www.w3.org/TR/1999/PR-rdf-schema-19990303/#intro as well as in > the later https://www.w3.org/1999/04/WebData and > https://www.w3.org/TR/schema-arch/ documents. > > The result of all this was pressure for RDFS to be a pretty minimalistic > language, one potentially replaceable, or elaborated upon later. This > also meant that there was a concern not to have too much RDFS leak into > the (hopefully uncontroversial) core of RDF, which needed to be > finalized and usable ASAP. That is roughly how we end up with things > like the "type" and "property" terminology being introduced in the RDF > M+S spec (and rdf: namespace), while structures making these ideas more > explicit (Class, Property etc.) were elaborated upon in "rdfs:" a little > later. As it happened, the M+S specification did make it to W3C REC > status in '99) whereas RDFS got stuck in limbo for a good while > afterwards, and only came back to formal life once W3C re-chartered the > Metadata Activity as the follow-on "Semantic Web" Activity in 2001. > https://lists.w3.org/Archives/Public/sw99/ has some bits and pieces from > that transition period. > > Nobody really liked rdf:Seq but it showed that order could be > represented in the graph structure, and the promise of "you could add a > utility vocabulary to express order differently" probably helped make it > bearable. > > </1990s>, > > Dan > > -- Antoine Zimmermann Institut Henri Fayol École des Mines de Saint-Étienne 158 cours Fauriel CS 62362 42023 Saint-Étienne Cedex 2 France Tél:+33(0)4 77 42 66 03 Fax:+33(0)4 77 42 66 66 http://www.emse.fr/~zimmermann/ Member of team Connected Intelligence, Laboratoire Hubert Curien
Received on Friday, 5 July 2019 10:04:52 UTC