- From: Leonard Will <L.Will@willpowerinfo.co.uk>
- Date: Wed, 29 Sep 2004 23:09:46 +0100
- To: public-esw-thes@w3.org
In message <20040929184124.GW2012@homer.w3.org> on Wed, 29 Sep 2004, Dan Brickley <danbri@w3.org> wrote > >Hi Stella, > >* Stella Dextre Clarke <sdclarke@lukehouse.demon.co.uk> [2004-09-29 18:20+0100] >> >> Sorry, but I am completely lost in this conversation. . . . >> I think I am saying you are asking for the moon, and any >>approximation to the moon could prove unsatisfactory. > >It's a tricky idea to explain, but I've seen enough RDF applications >that describe people and other entities directly that I know it's not a >moon-on-stick. So I think the problem is with communicating the basic idea I think that my position is much the same as Stella's - we both come from a background in traditional thesauri, and are having difficulty in coming to terms with the complexity that is being introduced in encoding schemes to make machines understand them. Can I crave your patience if I try to sort this out in my head from first principles? It seems to me that we have four things to build with: 1. concepts 2. attributes of concepts 3. relationships between concepts 4. attributes of relationships Attributes can be decomposed into further concepts and relationships, so that instead of saying that a particular person (an instance of the concept of "persons") has IBM as an employer, a height of 1.8m and an age of 52 years, we can represent these as relationships between the person and the concepts of "organisation", "height" and "age", respectively. The relationship with "organisation" is "employed by" and may have a date range as an attribute, while the relationships with height and age each have to contain a numeric value and a unit as attributes. >For cases like people, places, organisations, this is quite important, >since non-SKOS RDF can directly model some very detailed >characteristics of these entities. We can use non-SKOS RDF to describe >a Person's age, height, employer, etc.; or a place's latitute and >longitude, or an Organization's certifications. That's the sort of task >RDF was built for. So RDF to some extent keeps attributes of concepts undecomposed. A thesaurus or "authority file" can also do this, though it may express attributes as notes rather than in a more structured fashion. In a thesaurus the types of relationship between concepts that can be expressed are limited, and relationships do not generally have attributes. >SKOS uses W3C's Resource Description Framework (RDF) to describe >thesauri (and similar things). So does RDF provide a mechanism for recording all of the items 1 to 4 I have listed above? If so, I don't see why RDF has difficulty in encoding all the concepts of a thesaurus. You say >RDF's perspective on the world doesn't work so well "out of the box" >when trying to model things like fluids / mass nouns, or processes. So >there are often enough concepts in a thesaurus that don't have an >obvious correlation in non-SKOS RDF descriptions. Is this just saying that some of these more abstract or general concepts cannot easily be encoded in an RDF structure, or just that they may not often occur in particular existing ontologies that have been created using that structure? I think my difficulty is in grasping the way that RDF defines concepts. To me a concept is "a unit of thought" (the definition we have put in the draft revision of the British Standard for thesaurus construction). The scope of meaning of a concept within a thesaurus is given by its relationships and, preferably, by an explicit scope note. Al contrasts this with >The 'ontology style' which >describes things in terms of their properties (i.e. with *logical* >constructs). I really don't think that this is significantly different. A good scope note in a thesaurus defines a concept in terms of the broader category to which it belongs together with the properties that distinguish that concept from other concepts within the broader category. If, therefore, the idea of a "concept" is essentially the same in both types of scheme, I don't know why we need a special type of relationship to express exact or approximate equivalence when combining schemes or mapping between them, other than the relationship that would be used when combining or mapping schemes of the same type. >In other words, when people ask us "Should I be creating an Ontology or >a Thesaurus?", we want to figure out what to tell them (beyond "yes!") >about the diffent approaches possible using SKOS, RDF, OWL etc. And >hopefully have some conventions for connecting up information created in >either style. My hope is that rather than needing conventions for connecting up conflicting styles we can have an umbrella scheme where there is only one definition of each element (such as "concept"), and that we should have the components available to allow us to express any additional aspects, such as many types of relationship and attributes of concepts and relationships. A thesaurus structure such as SKOS would then just need a subset of these elements. (I have omitted discussion of facets and arrays, so as not to complicate the issue for the moment.) Leonard -- Willpower Information (Partners: Dr Leonard D Will, Sheena E Will) Information Management Consultants Tel: +44 (0)20 8372 0092 27 Calshot Way, Enfield, Middlesex EN2 7BQ, UK. Fax: +44 (0)870 051 7276 L.Will@Willpowerinfo.co.uk Sheena.Will@Willpowerinfo.co.uk ---------------- <URL:http://www.willpowerinfo.co.uk/> -----------------
Received on Wednesday, 29 September 2004 22:10:09 UTC