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Re: Hypermedia - Why

From: David Carlisle <davidc@nag.co.uk>
Date: Fri, 27 Jul 2012 12:00:49 +0100
Message-ID: <501274E1.5060708@nag.co.uk>
To: "Rushforth, Peter" <Peter.Rushforth@NRCan-RNCan.gc.ca>
Cc: "public-xmlhypermedia@w3.org" <public-xmlhypermedia@w3.org>
On 27/07/2012 11:04, Rushforth, Peter wrote:
> Hi David,

> For example, Atom Publishing protocol makes use of various hypermedia
> constructs,

It's fine for Atom (or HTML) to do this, they are languages/vocabularies
defined using XML syntax. That doesn't mean that it is OK for XML to do it.

>> XML isn't in itself a language, it is a framework for designing
>> languages
> Well, what we design with XML aren't really languages, are they?
> Maybe vocabularies would be more appropriate.

Whatever words you prefer, XML is at a different level than atom or html.

> Either way, vowels is the thing I think we're talking about here.
> And that's exactly the point, XML should give the users of that
> framework the tools to design their vocabularies appropriate to the
> environment. Schemas and namespaces are one way. The other way is
> the the way I'm proposing.

XML should as far as possible not pollute the vocabularies defined using
that syntax by forcing element and attribute names.

> Atom, for instance, does not use a schema, per se, just a public
> specification with required / permitted content layout. I would say
> it is a best practice for hypermedia design.

Same is true of HTML in the latest versions.

> As long as it is not the _only_ position, we can still talk.

yes cuts both ways though, you should also be prepared to contemplate a
mechanism that lets you declare that attributes have hypermedia
properties that does not use the blunt instrument of predefining certain
attribute names.

>> As I mentioned before, these reasons alone were the reasons for not
>> using xlink on languages such as xhtml2 being developed at the
>> time.
>> Chinese) or, closer to home, if all your attribute names did not
>> have a colon.
> Well, I imagine "xml" happens to show up in the Chinese xml from time
> to time, and what about xmlns etc? A little bit more won't hurt.
>> It also means (since only one such name is allocated) that you can
>>  not have two such attributes on the same element.
> We should ask the hypermedia community what *they* think. Not the
> XML community, strictly, although there is obviously an
> intersection.

I am not sure who you see as being the "hypermedia community" but HTML
claims to be the hypertext markup language so might be part of that
community and certainly (although I wasn't in the WG) the fact that you
could not model
<img src="foo" longdesc="bar"/>
in xlink because it requires two URI on the same element was a _major_
reason for blocking the adoption of xlink in (X)HTML at the time.

>> If you want to say attribute foo="example.com" is a link of a
>> certain type, you should define a schema type representing that and
>> then apply that schema to the instance. (Or if not XSD specify a
>> different annotation mechanism). What you should not do is say "if
>> you want to make a link the attribute has to have fixed name
>> xxxxx".
> I personally have nothing against XSD, nor schemas of any kind in
> general. In fact, the bugzilla bug I wrote included a schema to
> describe these vowels. I'm a pointy bracket guy! But I think schemas
> and namespaces are what we want to avoid in this case. If you want to
> do that with your vocabulary, so as to have control over the names of
> attributes, elements, what have you, go ahead, the facilities are
> there already in XML. What we want here are some hypermedia
> affordance vowels which reflect the architectural style of the web,
> as we know it today, and that we can refer to in our vocabularies,
> _by specification_, not schema.

It doesn't have to be a schema: just some declarative method that lets
you say which attributes have which properties.
The HTML group at the time proposed an extended css declaration syntax
as I recall as a counter-proposal to xlink.

ah found it: "clink" eg this discussion


Or the original opera proposal from 2000 that states right up front:

> There are three key differences between Clink and Xlink. First,
> Clink is a much simpler language not capable of describing the more
> advanced features of Xlink. Second, Clink does not require markup
> languages to change their syntax in order to describe linking
> behavior. Third, Xlink has some functionality which goes beyond
> Xlink, namely HTML's longdesc attribute and base element.


You see, nothing I have said in this thread has not been said dozens of
times before by different people in different decades.


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Received on Friday, 27 July 2012 11:01:21 UTC

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