- From: <noah_mendelsohn@us.ibm.com>
- Date: Tue, 19 Mar 2002 21:21:33 -0500
- To: Mark Baker <distobj@acm.org>
- Cc: david.orchard@bea.com (David Orchard), www-tag@w3.org
Mark Baker asks: >> Why is it (comparing anyUri's) any of XML's business? Because schema has an "enumeration" facet which allows you to build "enumerated" subtypes. The question is, if I build a subtype of anyUri that accepts only: "http://www.ibm.com" will it also accept uppercase? That's surely a question for which schema needs an answer. The other place this comes up is in the so-called key/keyref constructions, where we can assert that the value of one element or attribute must match that of another somewhere else in the document. David's proposal, with which I concur is "no", schema shouldn't have to know about every URI scheme and its rules. For purposes of the enumeration facet, string compare it is. I think anything else is impractical within the sorts of settings where schema validation is done. Schema is explicit that the notion of equality that we have for our datatypes is not always that which might be wanted for applications (let's not start a schema flame war here.) We have some related problems in dealing with -0.0 and +0.0 in IEEE floating point, for example, though I don't remember the details. We fully expect that applications using schema validated data will use exactly the IEEE rules of negative and positive zero, as we would expect web applications to respect the scheme's rules for URI comparison. When computing enumerations, we need to make some practical compromises. ------------------------------------------------------------------ Noah Mendelsohn Voice: 1-617-693-4036 IBM Corporation Fax: 1-617-693-8676 One Rogers Street Cambridge, MA 02142 ------------------------------------------------------------------ Mark Baker <distobj@acm.org> Sent by: www-tag-request@w3.org 03/19/2002 09:19 PM To: david.orchard@bea.com (David Orchard) cc: www-tag@w3.org, (bcc: Noah Mendelsohn/Cambridge/IBM) Subject: Re: "canonical" URIs Dave, > TAG members, > > I don't see URI comparison officially listed as a TAG issue. I'd like > Joseph/Stephen's issue added to the TAG issues list. > > Equivalence rules for URIs are defined by the URI scheme. Not all of them. DAML can be used to assert equivalence about any resources. HTTP redirection can be used for the same purposes, for resources other than those using the HTTP URI scheme. I recall a TimBL message where he enumerated the possible layers of equivalence. Can't find it though. > HTTP has a > section on URI comparison. > > However, XML does not have a default comparison function for the XML Schema > anyURI data type. I think a reasonable approach would be to say that the > default comparision function for anyURI is to use the HTTP URI comparison > algorithm, but that it is overridable by any scheme. Why is it any of XML's business? RFC 2396 already says everything that needs saying; that syntactic comparison is a function of the URI scheme. If you don't recognize the URI scheme, you can only compare for an exact match. Of course, anyURI is a URI reference, not a URI. In order to compare two URI refs that aren't syntactically identical, I believe you would have to dereference them, as the media type is presumably the authority on whether the frag ids are case sensitive or not. Oh joy. 8-/ MB -- Mark Baker, Chief Science Officer, Planetfred, Inc. Ottawa, Ontario, CANADA. mbaker@planetfred.com http://www.markbaker.ca http://www.planetfred.com
Received on Tuesday, 19 March 2002 21:37:47 UTC