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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: XML-LINK and IDREF
 In message <0Zm96CAybpkzEwi6@l...> Richard Light writes: > While we're on the subject of linking, I'm intrigued about the status of > the IDREF attribute type in XML. Agreed. I had thought about this as well. It's not easy to see how both might be used fruitfully at the same time without confusion. Formally, my understanding of ID/IDREF is that it is part of XML-LANG and must be supported by XML-LANG processors ([50] Validity checks). The IDREF can only point to an ID in the same document (at least how I read it). Therefore one option is for implementers not to use XML-LINK and to use ID/IDREF for whatever purposes they wish (structural, annotation, and with whatever behaviour.) Although I'm not an SGML expert I imagine this is frequently done already. The advantage/characteristic of ID/IDREF is that checking is at syntactic level (i.e. parsers are required to analyse it). [I am not sure what status ID/IDREF has in WF documents, as it will only know which the IDs are if there is an ATTLIST, i.e. a DTD or DTD fragment is included]. > > In the SGML world, simple links within a document are mostly done with > IDREF -> ID, e.g.: It is part of the language. In XML-LINK we are introducing another part of the 'language.' > <div1 id="chap.beginnings"><head>New Beginnings</head> > <p> ... > ... > <p>As we saw earlier in <ref target="chap.beginnings">Chapter 5</ref>, > ... > > (where the TARGET attribute has type IDREFS). Browsers such as Panorama > recognise and support these links natively. 'Support' is presumably application-dependent. Presumably browsers have something like: ACTUATE="USER" SHOW="REPLACE" as default - if an IDREF is discovered it is announced to the user who can navigate from there. > > Is the intention in XML that IDREF(S) attributes are only supported "for > compatibility", and that the XML simple link should be used instead, > i.e.: > > ... > <p>As we saw earlier in <ref HREF="#chap.beginnings">Chapter 5</ref>, > ... XML-LINK can also point outside the document. > > (where REF is now defined as having attribute XML-LINK="simple") ? The implementer and author is obviously given more help and guidance for implementing links with XML-LINK sinec there are a number of attributes which will be well documented and where usage will develop. [There would be nothing to stop DTD authors including ROLE, ACTUATE, SHOW with IDREF but it would not be likely to be standard practice, whilst the usage of these with HREF presumably will have a good communality of purpose and implementation.]. > This obviously has implications for XML processors. Yes! The full XML-LINK spec is rather daunting for an implementer. In principle it could require writing something part of the way towards Hyper-G or HyTime. *How* far is what concerns me at present :-) So my present approach is to: - ignore ID/IDREF for my own DTDs - enable JUMBO to locate IDs. [Note this is not trivial, because not all parsers provide this information at present.] - not provide special support in JUMBO [the application programmer can find the IDREFs and build their own stuff if required.] - fully implement XML-LINK=SIMPLE (hopefully more or less on track at present.) - think furiously about EXTENDED. From what Eliot has written, I suspect it will be a lazy implementation - i.e. storing links as they are 'discovered' in documents and adding this information to nodes. It will be Web-like and unlikely to be a complete linkset unless it becomes very clear how these are created and used. P. -- Peter Murray-Rust, domestic net connection Virtual School of Molecular Sciences http://www.vsms.nottingham.ac.uk/ xml-dev: A list for W3C XML Developers Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ To unsubscribe, send to majordomo@i... the following message; unsubscribe xml-dev List coordinator, Henry Rzepa (rzepa@i...) 
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