- From: Danny Ayers <danny.ayers@gmail.com>
- Date: Mon, 25 Feb 2008 13:52:03 +0100
- To: "Roy T. Fielding" <fielding@gbiv.com>
- Cc: noah_mendelsohn@us.ibm.com, "W3C TAG" <www-tag@w3.org>
While they seem an interesting and potentially useful notion, I don't think Noah's Immutable Document Resources offer any practical help to the underlying problem. In fact, HttpRedirections-57 itself seems rather back-to-front, largely addressing potential solutions rather than starting back at the underlying question (yeah, ok, this is going back to httpRange-14 a bit). So here's my two cents. I suggest we forget trying to find a purely technical solution and just use a slightly different abstraction around what it means to be on the Web versus on the Semantic Web. It seems to me that if we take into consideration different kinds of consumer capability, the problem evaporates. Key to this I think is looking at what a link means in different contexts. (The practical upshot of what I suggest would be that a HTTP 200 is an option available for *all* kinds of resources, though publishers may choose to use the 303 redirect for resources where it's convenient). Roy asks whether "A key requirement of the Semantic Web is that URIs be used to identify resources unambiguously". Well, yes, I'd suggest it is, in exactly the same way the Web is dependent on an essentially unambiguous naming scheme - the resource identified and the URI are intimately bound, thanks to their somewhat circular, fixpoint kind of definition. On the other hand the relationship between a resource and the thing it stands for does have ambiguity - the publisher may be clear, but the consumer of such information is limited to making their best interpretation of whatever (ultimately human-readable) definitions the publisher has provided. But I think Roy does highlight the most important part of the issue when he says: [[ On the Web, millions of people mint URIs, and millions more use them in references. Millions of human beings, conversing over time, with an occasional URI thrown in to refer to a subject under discussion. ]] Ok, the Semantic Web is an extension of the existing (document-oriented) Web. Flipping that over, I think it's reasonable to consider the existing Web as a projection or view of (some subset of) the Semantic Web. >From this perspective, regular HTML links can been seen as expressions of (s, p, o) statements, where the predicate isn't explicitly typed. The relation can be typed, using the rel/rev attributes in concert with a HTML Meta Data profile - GRDDL is the nearest we have to a formalism for this. But it's common practice to use a kind of human-friendly implicit typing, for example using <a href="http://www.ics.uci.edu/~fielding/">Roy Fielding</a> to refer to a person. But I'm suggesting the Semantic Web *does* need to distinguish between Roy the person and Roy's homepage. A reasonable RDF expression of the link above might be something like: <> dc:related <http://www.ics.uci.edu/~fielding/> . [ foaf:name "Roy Fielding"; foaf:homepage <http://www.ics.uci.edu/~fielding/> ] . But does the (document) Web need to distinguish between Roy the person and Roy's homepage? Evidently not, given the utility of simple linkage like that above. The only way I can see to square this circle is to differentiate between two kinds of interpretation. For example: $ wget http://www.w3.org/People/Berners-Lee/card.n3#i ... HTTP request sent, awaiting response... 200 OK Web interpretation: this is somehow related to Tim Semantic Web interpretation: we got a 200, so this is about Tim - what does the RDF here say? If we'd got a 303, sure, we could follow the httpRange-14 resolution's interpretation. But I don't think we can realistically assume 200=Information Resource. I don't think this problem can be completely resolved with a technical trick at the HTTP layer. When I talk of "the Semantic Web" and "the Web" above I'm really using shorthand for "the consumer is armed with SW tools" and "the consumer only has document-oriented tools". Heuristics may provide RDF interpretations of material that hasn't been published with those interpretations in mind (like using dc:related or rdfs:seeAlso for HTML links), and browser rendering (e.g. as text) may provide document-oriented interpretations of material solely intended for machine consumption. When we get Tim's FOAF profile, it's possible to delve deeper with RDF-aware software than it is with RDF-unaware software. In other words, the Web only understands Information Resources. You need an expanded conceptual infrastructure to tease the description of a person in RDF statements from the "pre-Semantic" representation. This approach does look like content sniffing - but I don't think that really applies, it's more like: to find out about a resource, as well as following your nose, you might also need to use your eyes. Cheers, Danny. [1] http://roy.gbiv.com/untangled/2008/resource-resource-wherefore-art-thou-resource -- http://dannyayers.com ~ http://blogs.talis.com/nodalities/this_weeks_semantic_web/
Received on Monday, 25 February 2008 12:52:24 UTC