- From: Jeff Sussna <jeff.sussna@quokka.com>
- Date: Fri, 3 Mar 2000 16:18:44 -0800
- To: "'Dan Brickley'" <Daniel.Brickley@bristol.ac.uk>, Guha <guha@epinions-inc.com>
- Cc: www-rdf-interest <www-rdf-interest@w3.org>
It's interesting that, while there are two major forms of URI, URN and URL, only URL has been strongly used so far. It is designed to tell you where something is rather than what it is. I think this reflects the overal focus on physicality rather semantics on the current web. As we are seeing, the semantic web will need to deal with what things are. It remains to be seen how we implement reliable protocols for whatness. It's one thing to use ISBN to identify books. ISBN refers to some external, canonical, centrally managed identification mechanism. Do we refer to people by their Social Security numbers? That obviously doesn't work for anyone who's not an American? Or by a GUID constructed from the GPS location, date, and time at which they were born? A whole other approach, that might be more feasible, that comes out of my previous comments about reliable vs. canonical identification, is to build up an identification. For example, "the person who was born at such and such a time in such and such a place, was CEO of such and such a corporation at a given point in time, etc." RDF could certainly help here. By the way, this latter approach correlates with a particular concern I have in the privacy arena. Even if your identitity isn't known, if it's known that a single individual engaged in some set of activity on the net, at some point it becomes possible to "triangulate" your identity from that activity. Jeff -----Original Message----- From: Dan Brickley [mailto:Daniel.Brickley@bristol.ac.uk] Sent: Friday, March 03, 2000 4:02 PM To: Guha Cc: www-rdf-interest Subject: Re: Subclass of Thing/Resource On Fri, 3 Mar 2000, Guha wrote: > Tim, > > I think many of these questions center around > precisely defining what an RDF Resource Identifier > is supposed to be. > > I agree that we need to distinguish between RDF > Resource identifiers and URIs. A URI is a pretty formal object > (protocol + host + opaque string) whose definition pretty > concretely constrains what can have a URI. By > this definition, people, places, etc. cannot have URIs. Sorry Guha, you're quite definitively wrong on this last claim. I agree that we need more clarifications in this area, but the URI spec (as referenced from RDF Model and Syntax) is very clear on this point: From http://www.isi.edu/in-notes/rfc2396.txt [begin excerpt] Network Working Group T. Berners-Lee Request for Comments: 2396 MIT/LCS Updates: 1808, 1738 R. Fielding Category: Standards Track U.C. Irvine L. Masinter Xerox Corporation August 1998 Uniform Resource Identifiers (URI): Generic Syntax [...] Abstract A Uniform Resource Identifier (URI) is a compact string of characters for identifying an abstract or physical resource. This document defines the generic syntax of URI, including both absolute and relative forms, and guidelines for their use; it revises and replaces the generic definitions in RFC 1738 and RFC 1808. [...] Resource 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. The resource is the conceptual mapping to an entity or set of entities, not necessarily the entity which corresponds to that mapping at any particular instance in time. Thus, a resource can remain constant even when its content---the entities to which it currently corresponds---changes over time, provided that the conceptual mapping is not changed in the process. [end excerpt] > > On the other hand, it would be very convenient to have > a unique canonical identifier for refering to the one TimBL > or one RalphSwick. In my reading, this is what the RDF > Resource ID is. Everything (including literals, URIs, ...) could > potentially have one of these. Maybe, though I don't see any scenario whereby we'll end up with unique canonical identifiers for persons. Social/political/privacy issues aside, it's just too hard to do. That said, mailboxes, national insurance numbers etc allow us to say things like 'the person whose util:personalMailbox is mailto:guha@epinions...', uniquely picking out a flesh and blood person without (a) giving them a URI, (b) making a category mistake and conflating them with their mailbox URI. > > I do think it would be nice if an application can assume > some kind of structure to these identifiers, but not being > able to do so would not be fatal. > > I agree with you that http://foo.org/bar.rdf#xyz is a lousy > identifier for an object. To me, it just represents a position > is a file. '#' is a downright broken bit of web architecture. The '#' fragment/view semantics are defined as being relative to the mime type of the object. Since mime types can be content-negotiated, that's hairy since a single URI plus '#' doesn't mean much without additional assumptions about mime types. For example, http://www.w3.org/Icons/WWW/w3c_main has both GIF and PNG mime-typed variants. So the semantics of http://www.w3.org/Icons/WWW/w3c_main#foo can't be considered outside the context of some HTTP transaction, since the mime type of the resource isn't an instrinsic property of the resource identified. details: @mail:/users/pldab> telnet www.w3.org 80 Trying... Connected to www.w3.org. Escape character is '^]'. HEAD /Icons/WWW/w3c_main HTTP/1.1 Host: mybox.ilrt.bris.ac.uk Accept: application/x-fictional-mimetype HTTP/1.0 406 Not Acceptable Date: Fri, 03 Mar 2000 23:58:48 GMT Server: Apache/1.3.6 (Unix) PHP/3.0.11 Alternates: {"w3c_main.png" 0.7 {type image/png} {length 5904}}, {"w3c_main.gif" 0.5 {type image/gif} {length 5684}} Vary: negotiate, accept TCN: list Content-Type: text/html Again, the URI spec has words to say on this (unfortunately...): 4.1. Fragment Identifier When a URI reference is used to perform a retrieval action on the identified resource, the optional fragment identifier, separated from the URI by a crosshatch ("#") character, consists of additional reference information to be interpreted by the user agent after the retrieval action has been successfully completed. As such, it is not part of a URI, but is often used in conjunction with a URI. fragment = *uric The semantics of a fragment identifier is a property of the data resulting from a retrieval action, regardless of the type of URI used in the reference. Therefore, the format and interpretation of fragment identifiers is dependent on the media type [RFC2046] of the retrieval result. > In the long run, the object identifier namespace will have > to be like the DNS namespace. > > Reactions? We could do with a URI activity to fix some of this... > guha dan > > > >
Received on Friday, 3 March 2000 19:12:57 UTC