- From: Bill de hOra <bdehora@interx.com>
- Date: Wed, 17 Oct 2001 03:29:22 +0100
- To: <w3c-rdfcore-wg@w3.org>
Hi Pat, lots of questions... Pat Hayes: >> You say there: "Clearly in RDF processing, literals are opaque to RDF (i.e. if a literal looks like a URI or more RDF, it is treated as a literal, not as a URI or more RDF). However an application using RDF triples and able to properly manipulate Dublin Core in your example would be entitled to draw the inference that the literal names an entity." I want to take issue with this, because to me it seems to contradict itself. As you say, to an RDF processor, literals are opaque. But you then say that an 'application using RDF triples' would be entitled to draw an inference which requires (?) NOT treating literals as opaque if they refer to the Dublin core. Is this application supposed to be an RDF application or not? If it is, then it is not entitled to make that inference, since there is nothing in the RDF that enables it to draw it. If on the other hand it is able to draw that conclusion, then it evidently is not using information (only) from the RDF triples, so why should an account of the RDF meanings of the triples be concerned with this information? >> When I say opaque, I mean a parser cannot treat the literal as anything other than a literal. What the application/engine/person does with the triple is its own business. I appreciate that a clean delineation between parsers and engines isn't always the case. A strawman. With my A. Haxor hat on, I read the DC creator description in order to write some code for a dodgy KM module which tries lifts a literal from bytes/string/Unicode/whatever we decide literals are, into denoting a person that has a URI denoting them. So the code's job is to bind dc creator values to RDF resources. Someone might say 'Bill, what on earth is this code doing? You should get the assumptions out of the code and write them down'. I could point to my code and say, 'But it works, the worst that happens is that it says it couldn't find anyone, and anyway, Dublin Core didn't write their assumptions down either, it's not my fault we use it'. Maybe that's not an RDF application, and that's a kind of realpolitik hacking we wish to discourage or someday make unnecessary, but I conjecture there will lots of abductive code like this for some years to come for the express purpose of scraping over existing data: it's the stuff of business models. Old data never dies, it just gets integrated. Pat: >> I think this is particularly tricky as an example since the part of the Dublin core that you quote is written in English, so presumably is not fully understandable by any software yet written by anyone. >> I think any examples working out of natural language are tricky. Are there better examples we could use for the Primer? Pat: >> >Bill: >[Indeed most of the examples I've seen of literal values have literals >naming an entity in a common-sense way. Yes that's folkware semantics >but there's nothing wrong with common-sense just because computers don't >have any. There is if you are touting the formalism as something for computers to use. In fact it is dishonest and foolish, and would be valid grounds for having ones tenure case dismissed at any reputable university department. >> I'm tempted to quote Groucho Marx. I was referring to common-sense as an aid to following the example in the primer, not attributing magic powers to RDF. In the meantime someone's going to have to explain to me how we get from common-sense examples to RDF triples in this primer without some form of conjuring. There _is_ magic dust being sprinkled over Frank's examples and the ones in the M&S. What exactly is wrong with doing this as long as we point that out? Pat: >> >Bill: >In any case it's up to the modeller (in this case, the primer) >to make the semantics explicit. Surely that's what RDF is for?] > >Anyway. There is _nothing_ in RDF to make us think that when a property >has a literal value the property means the literal itself is the entity >and not what the value might denote True, but what it can denote is severely restricted. The model theory at present assumes that literals have a *fixed value*. So whatever a literal denotes, it has to denote it once and for all, globally. It can't denote one thing in the Dublin core and something else somewhere else. >> I'm not suggesting that a literal should denote different things. I'm suggesting its reasonable for a parser to treat a literal as a blob and an application not to. As far as I'm concerned a parser's job is to get literals into working memory as literals; what's done in working memory with those literals, is another matter. Maybe they get served up to a person who realises the literal is actually someone they know, maybe there's a bug in the application code that gets the literal lifted, maybe someday someone will specify DC creator more formally that will allow machinery to infer that a literal hanging off dc:creator can stand for a person. Lifting literals via some kind of (I don't know, abductive?) inference is something people are going to want to do with RDF. Pat: >> Now, that is a very simple and restrictive assumption, and Peter Patel-Schneider wants us to relax it to the extent of allowing datatype schemas for literals. The kind of examples he uses are where "070801" might mean either a date or a string or an integer, and one can determine from things like the rdfs:range information which datatype scheme is supposed to be applied to each literal occurrence. That is the scheme we have now worked out in full detail so that it COULD be incorporated into the MT for RDFS, if we want to do so, though right now its just kind of waiting to be put there. But even with this extension, the range of things that a literal can refer to is somewhat restricted to be the kinds of things that one finds in datatyping schemes. I'm not sure if having a literal like "creator" denote a particular human being would count as a datatyping scheme, but it sure doesn't sound like one to me. >> I'm confused here. Are you saying that you can't soundly get from a literal to a thing in the world? If not, was there ever any point in basing DC creator on RDF? Pat: >> >In Frank's example, without clear semantics for 'creator' there isn't >enough information to make a decision on what's being implied. Right, and indeed that semantic content cannot be stated in RDF. I don't think we should pretend that it can if in fact it cannot. >> Does that invalidate Frank's and the M&S' examples? If it doesn't then I don't understand why and if it does how are we going to bootstrap this primer for oikes like myself? Pat: >> I think we should be very careful not to give the impression that we are saying that RDF can represent natural language meanings. It would be irresponsible, or just plain silly, to claim that existential-conjunctive logic can represent every meaning expressible in natural language. (If you think it can, then try publishing that claim in a refereed journal.) >> I know enough not to claim that. But that seems to make using any natural language example to pluck out a triple in the primer RDF snake oil. regards, Bill .. InterX bdehora at interx.com +44(0)20-8817-4039 www.interx.com
Received on Tuesday, 16 October 2001 22:32:01 UTC