[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Public Identifiers
I've hesitated jumping in to the discussion since the SIG went through it in detail so long ago, but something discussed back then has not been raised in this forum where there are other participants who didn't see the earlier discussions. At 98/09/18 06:49 -0500, W. Eliot Kimber wrote: >In hindsight, it's clear to me that we never should have allowed public IDs >in XML. Two uses of Public Identifiers that have, I believe, been overlooked throughout this discussion, and I feel I personally need, are (1) receiver/user resolution when system id unavailable and (2) copy identification (e.g. versioning). (1) Consider I have an XML document on a CD-ROM (or password-protected for write, or behind a firewall for write permissions, or some other condition rendering it read-only). It might be very large, so large I don't want to copy it to a local environment where I can modifiy it. I may not even have permission to make a local copy in which I can modify it. Now, some external resource refered to in the read-only file is identified by both a SYSTEM identifier and a PUBLIC identifier: <!DOCTYPE pres PUBLIC "+//ISBN 1-894049::CSL::Presentations//DTD Presentation//EN" SYSTEM "http://www.CraneSoftwrights.com/shareware/presdev/pres.dtd"> The XML Processor discovers it cannot access the URL for whatever reason (server down, firewall, whatever). A Public Identifier Resolution Mechanism, if it were available in the XML Processor, can obtain the necessary local copy if I give it information about a copy I made some previous time when I did have access to the remote resource. And by changing the information to the resolution mechanism, I can move it around freely without changing the read-only resource. Without a public identifier, and without the ability to modify the read-only resource, I would have to resort to some kind of System Identifier remapping mechanism if it were available in the XML Processor. I would think it "cleaner" to do public identifer mapping, rather than system identifier remapping, though I will acknowledge both will end up with the same results. (2) In the life of a DTD, I may create a number of instances conforming to different versions: One day: <!DOCTYPE RDF PUBLIC "+//IDN w3.org//DTD RDF Version 1.0//EN" SYSTEM "file:///s|/rdf/rdf.dtd"> Three months later: <!DOCTYPE RDF PUBLIC "+//IDN w3.org//DTD RDF Version 1.1//EN" SYSTEM "file:///s|/rdf/rdf.dtd"> Three months after that: <!DOCTYPE RDF PUBLIC "+//IDN w3.org//DTD RDF Version 2.0//EN" SYSTEM "file:///s|/rdf/rdf.dtd"> Each one pointing to the same file that has been updated on the fly. One feature of an XML Processor might be that if an error is detected through the use of the resource found through the SYSTEM id, offer to the user to begin processing again through the resource found through the PUBLIC id without obliging the user to change the source file. I'm emphasizing the temporary nature of this feature, perhaps because this is a one-off run for the user. For conformance reasons the governing DTD is the one found through the SYSTEM identifier, so it shouldn't be default behaviour of a processor to categorically "try again" with the PUBLIC identifier when there is a fault using the SYSTEM identifier ... but a courtesy "restart with override" feature might be offered once the conformance requirement to stop has been met. This second issue is fuzzy, but I hope I've conveyed how the following resolution of the public identifiers would help: PUBLIC "+//IDN w3.org//DTD RDF Version 1.0//EN" "file:///s|/rdf/rdf-1-0.dtd" PUBLIC "+//IDN w3.org//DTD RDF Version 1.1//EN" "file:///s|/rdf/rdf-1-1.dtd" I'm more interested in the utility of the first issue. To me it makes more sense to map public identifiers than remap system identifiers. ............. Ken -- G. Ken Holman mailto:gkholman@C... Crane Softwrights Ltd. http://www.CraneSoftwrights.com/x/ Box 266, V: +1(613)489-0999 Kars, Ontario CANADA K0A-2E0 F: +1(613)489-0995 Training: http://www.CraneSoftwrights.com/x/schedule.htm Resources: http://www.CraneSoftwrights.com/x/resources.htm Shareware: http://www.CraneSoftwrights.com/x/shareware.htm xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
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