- From: pat hayes <phayes@ai.uwf.edu>
- Date: Fri, 4 Apr 2003 18:27:32 -0600
- To: Michael Mealling <michael@neonym.net>
- Cc: Graham Klyne <gk@ninebynine.org>, w3c-rdfcore-wg@w3.org, www-webont-wg@w3.org, timbl@w3.org, Dan Connolly <connolly@w3.org>, public-uri-cg@w3.org
- Message-Id: <p05111b26bab3b9593648@[10.0.100.86]>
>On Fri, 2003-04-04 at 16:06, pat hayes wrote: >> (Im CCing this to people outside the RDF Core WG as the issue is much >> larger than just for RDF. Please be selective in CCing replies in >> order to avoid cross-list postings, thanks. -Pat) > >> > >> >FYI, the URI CG is now officially chartered. >> > >> > URI Coordination Group >> > http://www.w3.org/2001/12/URI/ >> > >> >"The mission of this group is to coordinate ongoing work in the area of >> >Uniform Resource Identifiers (URIs); to serve as a coordinating body of >> >all issues involving URIs in the W3C and act as the coordinating body >> >for URI issues with other groups. >> > >> >... >> > >> >Back in the mists of 2002, I volunteered to act as RDFcore liaison >> >for this group. >> > >> >As yet, there's been little activity. It might be worth noting that >> >Roy Fielding is working on a revision to RFC2396 (version available > > >at: http://www.apache.org/~fielding/uri/rev-2002/rfc2396bis.html). >> > >> >The IETF URI BOF (a week or so ago) also had some discussion or IRIs. >> > >> >There were a couple of things raised at the IETF meeting that may be >> >of relevance to RDFcore: >> > >> >(1) a suggestion that "resources" don't exist unless a URI is >> >defined for them. (I raised an objection to this --because we have >> >bnodes-- which was somewhat brushed aside with "If RDF has a problem >> >with URIs its RDF's problem not URI's problem. Since the matter is >> >more philosophical than of practical import, I don't think it's a >> >big deal.) > >Hi, I'm the one that made that comment and I'll stick by it. The issue >is not that I'm denying that resources as __YOU__ are defining them >exist. I'm not using any other definition of the term other than the one >found in RFC 2396. Neither am I. I never have used any other definition, which is why this issue is so important. That text (repeated in Fielding's draft referred to above) reads as follows: "A resource can be anything that has identity. Familiar examples include an electronic document, an image, a service (e.g., "today's weather report for Los Angeles"), and a collection of other resources. Not all resources are network "retrievable"; e.g., human beings, corporations, and bound books in a library can also be considered resources. " Now, it is clear from this that 'resource' is intended not to be restricted to things that are web-retrievable, but is intended to refer to *anything* which can possibly be given an identifier (not that already has an identifier: most human beings don't have a URI). Other W3C working groups have determined that this includes imaginary things (unicorns) and abstractions (properties, classes) as well as things that may exist in the future or past. In fact, that phrase 'anything that has an identity' seems to mean literally anything, unless the word 'identity' is being used in some nonstandard way, and there is nothing in the rest of RFC 2396 to indicate that it is. >If it will help we can change the term used in RFC >2396. URIs identify 'froogles'. 'Froogles' are defined as things that >are identified by URIs. It is up to your system to scope and extend the >definition of a 'froogle' to match your systems needs. But that extended >definition is _scoped_ to your application, not to the entire system of >URIs and 'froogles'. Fine; I am treating the word 'resource' in much this way, since it has no predefined meaning. But the problem I have is that the scope of RFC 2396 (or whatever you guys do) *is* the entire system, so if RFC 2396 (or you) restrict the notion of 'froogle', we ALL get restricted. The issue at hand is whether or not froogles can exist which have no URI. If you say no, then we don't have the option of overriding you on that; and that restriction would be disastrous to just about every use of a database or inference engine on the Web, and also, if taken seriously, to many web services models and other applications. > > But this IS a VERY big deal, and we should raise hell about it, and >> not stop raising hell until this idea is abandoned. This decision >> would be a disaster not just for RDF but for almost any web logic. It >> would force all web logics to treat resources as temporal entities >> which come into existence at a time (and maybe go out of existence >> and reappear later). > >Then you are using the term 'resource' to mean something that is >completely out of scope of RFC 2396. I profoundly disagree. First, the text of RFC 2396 seems to go to some length to not restrict the scope of the term in any way at all. Second, nothing in RFC 2396 says or implies that resources come into existence when they are assigned a URI. The text of RFC 2396 is clear on casting the net of 'resource' extremely wide, and this interpretation has been borne out in many subsequent email discussions and even in formal decisions made by working groups. I think that you are interpreting the language of RFC 2396 far too narrowly. >The problem here is that we're >having a terminology collision, not an architectural problem. I am using the term in the way that it is used throughout large sections of the W3C technical community. The word is a term of art within the W3C and does not have a clear predetermined meaning; but it is abundantly clear that it does NOT refer only to things that are (a) web-retrievable, or (b) have been assigned a URI at any given point in time. Entire W3C standardization efforts depend crucially on the fact that the set of 'resources' includes things that may not currently have (but can be given) URIs; and virtually all of the proposed and existing semantic web reasoners depend on the ability to quantify over things that have no URI. The issue was discussed at length by the RDF working group, and would have been discussed again by the Webont WG if RDF had not got it sorted out. And this isn't just RDF's business: all these WGs are required to conform to RFC 2396 (or whatever you guys do to replace it) so if you impose restrictions on what a 'resource' is then all these other efforts are hamstrung by those restrictions. > > This plays havoc with ALL quantified logics, not >> just RDF. It effectively makes all current mechanical reasoners >> invalid (since they all use, one way or another, the principles >> underlying existential quantification.) It also plays havoc with all >> semantics for NL dialog and just about everything else. It would >> drive a truck through all assertional datatyping and most attempts to >> do syntax layering (such as the OWL/RDF mappings and any future >> son-of-OWL/RDF mappings.) It is not just an obscure philosophical >> niggle: it is absolutely fundamental. > >Again, those things aren't using the term 'resource' the way it is used >in RFC 2396. Please get that _CLEAR_. I have it clear, and they ARE using it in that way. There are now about a dozen W3C documents in last call which use it in this way, referring to RFC 2396. I wrote one of them myself. The RDF M&S document uses it in this way and has been publicly available for four years. Please, allow me to ask you in return to not confuse issues concerning URIs with those concerning resources, and to take the text of RFC 2396 more seriously. That stuff in the intro parts of RFC 2396 isn't just chit-chat. >RFC 2396 says nothing about >knowledge systems of any kind, way, shape, form or fashion. That is not the point; but in any case, it does, in fact, although indirectly and implicitly, because it talks about names and what they refer to, and names are fundamental to 'knowledge systems' (I presume you mean inference systems). RDF for example is required to use URIs as names. So it has to conform to RFC 2396. >The only >thing RFC 2396 defines is the fact that there is an identifier and it >identifies whatever it is it identifies. No, it also says something about what KIND of thing can be identified. It also, by the way, thereby implies quite a lot about what 'identifies' means. It does not (only) mean 'identifier' in the narrow sense in which it is used in programming languages; it means it in the sense in which logical and assertional languages refer or denote. That is a very different sense of 'identify', and it obeys different semantic rules. And to repeat, this isn't what _I_ say: it is what RFC 2396 says, and it reflects the facts of the matter in the way that URIs (particularly URNs) are actually used on the Web. >If you build a system that >constrains that further then that is the intended purpose. The thing you >CANNOT do is impose your definition on others. I am not imposing anything on others. I am only asking that in your role as a member of the coordinating group, you pay some close attention to the ways that URIrefs are actually being used on the Web, and avoid making de novo rulings which violate both the intentions and the practice of the actual web. > > >> For one (tiny) example of the trouble it would cause, try making >> sense of this idea in the context of a URI scheme for identifying >> dates and times. If nobody has perviously mentioned 3.48 am on the >> 24th of February, 1865, does that date suddenly come into existence >> at the time someone one first mentions it with a URI? > >Within the formal system defined in RFC 2396 that contains only two >concepts: a URI and its Resource, no. You're talking about a much richer >formal system and within _that_ scope you are completely correct. I am not talking about any formal system. I am talking about the _resources_, the actual things in the world, that the formal system talks _about_. Using a richer formal system doesn't make the world more complicated, it just enables you to say more about it. The resources are not formal constructions, they are the actual things in the actual world: real physical books, real living people, galaxies, times, places, countries, sodium atoms, bottles of wine, whatever. Really, they are: RFC 2396 asserts that that is what they are. So if you start restricting this to some narrow subset of things, that imposes a huge constraint on ALL other uses of URIs in ALL other Web languages and formalisms. RDF (for example) is not free to invent new kinds of things to be its resources: it has to conform to RFC 2396. If they are restricted to some small class of things, or required to obey some narrow strictures about existence, then RDF (and RDFS and OWL and OIL and DAML, to name a few at random) are automatically restricted in their meanings. Users of these languages will have two options: to ignore what the coordinating group says about URIs, or to become in effect useless. I would suspect that they will in fact do the former, which would be rather a pitiable outcome of an effort to coordinate the use of URIs. > > What if someone >> has mentioned the year 1865? Did that particular year have a >> minute-length hole in it, which has just gotten filled in? Don't >> laugh when your temporal reasoner figures out that you don't need to >> get to the airport until a minute after the flight leaves. > >AGain, you're including concepts such as 'someone', 'year', 'minute', >'hole' which are not defined in RFC 2396. It only defines two things: a >URI and the thing identified by it. Nothing more. Im not asking RFC 2396 (or you) to *define* anything. Im only asking you to be careful not to *exclude* any of these things. Saying that resources must have URIs effectively excludes most of these things, since most of them they don't as yet have URIs assigned to them, and many of them never will. You would run out of namespace if you tried to assign a URI to every protein molecule. So if we follow your ruling, they don't exist. But they DO exist, and we may NEED to refer to them; or, more subtly, we may need to be able to reason about their existence even when they do not have a URI, in order to decide to assign them a URI so that we can refer to them. One of the moves that a query-answering engine might make, for example (explicitly part of the recently defined DQL protocol) is to infer that something exists which satisfies a query, then *assign it* a new URI, and use that URI to answer the query. With your restriction on the meaning of 'resource', that would be rendered either invalid or impossible. > > This group needs to pay some serious attention to what it is talking >> about. Fielding's draft cited above repeats verbatim the extremely >> grandiose and rather wooly text from RFC 2369 claiming that >> 'resources' are anything that can possibly exist, on the web or off >> it. It is irrational and incoherent to assert this and also treat > > resources as though they were datastructures or computational >> constructs of some kind. If the group's attitude to issues like this >> is that these are just philosophical niggles of no real consequence, >> then the best thing this group could do would be to disband itself >> before it does more harm, or at the very least try co-opting someone >> who knows something about what the issues are here. URIs are too >> important to be left to syntactical engineers. > >URIs are used in large numbers of places where the only valid thing is a >syntactic engineer. Not that it is really germane to the discussion, but I would dispute that. Usually, somewhere along the line, URIs are used to refer in some way. If they were not, they wouldn't be a great deal of use. >You cannot redefine intended simplicity of URIs to >accomodate your needs to the detriment I am not wanting to redefine URIs at all. I have no opinions about URI syntax, and have no desire to redefine or complicate it. I am making a point about the meaning of "resource". "Resource" is a semantic notion, not a syntactic one. OK, if you are not interested in semantics, that is fine: I have no quarrel with you. But please don't make damaging semantic pronouncements if you are concerned primarily with syntax. >of things that explicitly reject >the concepts you are talking about. What "explictly rejects" the idea that URIs refer to resources? That seems to be central to the very idea of a URI, according to RFC 2396. And how would allowing more things to count as resources be detrimental to any application? >There are other data models out >there and URIs were designed to work with ALL of them, not just a few of >them.... I want URIs to work with all of them. But in order to do that, they must be capable of referring as broadly as possible. By restricting the notion of resource you are not helping URI syntax in any way at all, but you are with a casual stroke of the pen effectively prohibiting any Web application from referring to most things in the universe. Pat Hayes -- --------------------------------------------------------------------- IHMC (850)434 8903 or (650)494 3973 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32501 (850)291 0667 cell phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayes s.pam@ai.uwf.edu for spam
Received on Friday, 4 April 2003 19:29:03 UTC