From: Peter F. Patel-Schneider (pfps@research.bell-labs.com)
Date: 02/12/04
From: Sandro Hawke <sandro@w3.org> Subject: Multiple Semantic Web Languages (was: Re: reifying variables) Date: Thu, 12 Feb 2004 11:43:21 -0500 > > > I argued long and loud in the W3C WebOnt working group about problems that > > using the RDF syntax caused. This argument didn't go anywhere, so I gave > > in and created a partial solution for OWL. > > Do you remember why the WG disagreed with you? Because all Semantic Web langauges have to be same-syntax extensions of RDF. > > > I've > > > sometimes campaigned unsuccessfully for a standard meta-language, in > > > which the syntax and semantics of practical data languages are > > > described. > > > > XML might be the syntax half of this. Isn't model theory (or even > > mathematics) the semantics half? :-) > > Ah, I meant a machine-usable meta-language. Like java byte code, > XSLT, or prolog DCGs -- something you can use to define a new language > such that computers can simply use the new language without human > assistance. Well, XML still works for the syntax side. I don't think that you are going to have much luck on the semantics side. > > > In any case, using an "RDF-Like" syntax is using counterfeit money and > > > I suspect is only accepted as the price of admission by mistake. I > > > apologize for not noticing and commenting on SWRL doing this back in > > > November. > > > > There have been several proposals to make this sort of solution the > > official one, including things like dark triples. > > "Dark triples" was proposed during a time when RDF Semantics were > rather up in the air, I think. It's less in-order now. No. Dark triples were proposed when the RDF Semantics was pretty much determined. They were always a way of escaping from the semantics. > > I would very much welcome a statement from W3C that Semantic > > Web languages do not have to be written in triples (or quads, or quints, > > ..., as in several recent proposals). > > The consortium doesn't have many ways to make statements like that. Then what is Architecture of the World Wide Web, First Edition (http://www.w3.org/TR/webarch/) supposed to be? > Maybe the closest would be in the charter of a new working group or > activity. In fact, the SWRL WG charter I floated a few months ago > had some words about the extent to which the language needed to be > based on RDF. > > What I had in mind were rules like in n3, of the form > forall u1, u2, ... > { rdf graph } > => > exists e1, e2, ... > { rdf graph } > > where the rule itself did NOT have to be conveyed in RDF. (I want > them to viewable as RDF, and I believe it's possible, but we didn't > want the WG to be forced to do that.) > > I was interested in seeing if the rule language would itself turn out > to be a better RDF serialization language. > > Had this been given to the membership, and had the membership approved > it, I suppose you would have had much of what you want. > > > In more general terms, I think what qualifies or does not qualify as a > Semantic Web language is a complex social question. What TimBL says > in speaches probably counts for a lot, what the consortium members say > in WG charters counts for a lot, but so does ... everything else. > > And cool, useful, deployed, working systems speak very, very loudly. > > > > > You would agree there's a cost to each new language, right? > > > > No. I do not believe that there is a net cost for most new > > languages/representations. New languages/representations are accepted in > > part because of problems with existing languages/representations. If the > > new language/representation does not have benefits outweighing its costs, > > it is unlikely to be accepted. > > You changed "cost" to "net cost". Big difference. Well, I would argue that even the gross cost is quite low, and in fact, may indeed be negative, particularly if the new language replaces an ugly botch (read RDF/XML here). > You're right about net cost; I was thinking about up-front costs or > barriers to entry. Every new language that agents (eg browsers) need > to know makes the cost of developing a new agent higher. But you're > right that the market will decide and people will implement at least > dozens of languages if the benefit is there. And plugins help a bit. > Part of the role of the W3C is to try to cut down the number of > languages -- one scalable vector graphics language instead of four -- > to keep this up-front cost in check. This is something software > vendors and user communities really want. > > There are also costs to users of upgrading their software, and costs > to developers of learning to use a new language. There are great > network effects when more and more people use the same language. > Bookstores can label the shelf, instead of just having to hide the > books on each little language in Miscellaneous/Oversize. > > So I'm all for people competing with RDF/XML in the hopes they come up > with something really better, but we should recognize that it's mostly > a winner-take-all proposition, and we can't expect to let a thousand > Semantic Web languages bloom (except via the meta-language approach, > perhaps). > > > All of this is perhaps irrelevant to the original "reification of > variables" question, since a logic language with its syntax encoded in > RDF can hardly be said to be itself RDF. It is its own language, with > its own deployment and cost issues, even if carried on RDF/XML. All I > was saying was that IF you're going to encode the syntax for the > language in RDF, for whatever reason, please encode it in real RDF > (with real RDF semantics [plus iron]), not in an RDF-like language > with insidious differences from the standard. Well, the problem, as I see it, is that RDF encoding is mandated, but RDF embedding is impossible, so the only solution is the solution embodied in SWRL. > -- sandro peter
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