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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: xml:href, xml:rel and xml:type
 On Thu, 2012-04-19 at 14:37 +0000, Rushforth, Peter wrote: > The point is, the media type advertisement > that is present in @xml:type _tells_ the crawler, or any other client, > if they will be able to understand what is at the other end of the > @xml:href. You can never assume that the result of fetching a resource will be a particular representation format. You might actually get anything back at all. For sure you might get HTML 2 or HTML 4 as part of an HTTP 404 or 401 response, but content negotiation means you might get image/jpeg instead. Instead, it tells the client that the document author _expected_ a particular type. If we can agree that far maybe we can make progress on understanding each other ;-) I'm personally interested in typed links, where the types are rhetorical in nature - e.g. "supports", "disagrees", or express other relationships. > One could write an ISO 19115:2003 crawler, for example, > and so long as the links were annotated with @xml:type, the > crawler could target that media type only, processing the elements in the > way it understands them, doing whatever it needs to do to meet its > goals (this might not be "search", in the google sense, for example). Someone else would write a crawler that checked out all the links and fond the 90% that you'd missed, e.g. when you go to www.findmylover.com and you get an HTML page that asks for a country, and then www.findmylover.com/?country=rohan returns your geographical markup language. It's dynamic, not static. > > Media type tells you what something is, not how to process > > it. There are lots of things you can do with an SVG image, > > for example, besides simply rendering it. > > Media type (@xml:type) tells you what the media type of the advertised linked > representation might be (not: _is_), so you know if you should be able to process it. When I wrote Media type I was referring to the label in the returned HTTP header, which is authoritative. > An SVG image might be chosen over a png version so the client could edit > the vectors, for example. The media type advertisement allows clients > to know if they can send an Accept header with a value supporting that > use. The client can *always* send an Accept header saying they prefer PNG to SVG. (content negotiation is of course different from "HTTP OPTIONS") [...] > For sure, that is what the Accept header is for. But the html author uses > the link to his own ends, and it sure isn't constrained to html. > For xml, where everyone mints his own media type effectively, @xml:type > is essential. Maybe this is where I'm not following your argument. Are you suggesting people would register individual schemas/vocabularies with IANA themselves, or would use types like application/x-mallard+xml ? > Exactly. Adding no-namespace-declaration hyperlinks is a big win, IMHO. Is the problem the namespace declaration? There was talk about that a year or two ago on xml-dev, about reforming namespaces, but there's too much XML 1.0 inertia to make it easy. > xml:type isn't putting the media type into the link. It's advertising > a representation format available from the URI. Very much link > atom:link@type. Why has atom:link grown beyond atom? Because > there is no equivalent thing in xml. Hmm, I have not seen atom:link in use outside atom, I'd be interested to learn more about that and see examples. Note that we (W3C) did reduce the barrier of XLink a little, you only need one attribute now. And declaring an XLink namespace seems no worse than declaring an atom one to me. [...] > The biggest barrier to use of xml on the web is following web service > paradigms which don't use the web architecture to advantage. > And, not having hypertext there when you need it. I wonder if we got 20 people in a room together we could get agreement on "the biggest barrier"... :-) Web services are rapidly moving to JSON. Sorry for a long reply. Liam -- Liam Quin - XML Activity Lead, W3C, http://www.w3.org/People/Quin/ Pictures from old books: http://fromoldbooks.org/ 
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