W3C home > Mailing lists > Public > public-rdf-in-xhtml-tf@w3.org > March 2008

Re: RDFa test case #1 missing @profile?

From: Norman Walsh <ndw@nwalsh.com>
Date: Mon, 03 Mar 2008 16:55:52 -0500
To: "Mark Birbeck" <mark.birbeck@x-port.net>
Cc: RDFa <public-rdf-in-xhtml-tf@w3.org>
Message-ID: <m2mypfv5ef.fsf@nwalsh.com>
/ "Mark Birbeck" <mark.birbeck@x-port.net> was heard to say:
| The example you give uses @about and @property, neither of which
| exists in HTML or XHTML, but they do now exist in XHTML+RDFa. If an
| author uses either of these attributes then I think it's pretty clear
| that they are using XHTML+RDFa.

With equal respect, I have to disagree with you :-)

HTML has always ignored unknown elements and attributes. I could very
well have local content which uses @about and @property, or <xyzzy>
for that matter. I might very well have invented it independently from
the RDFa task force and I might have assigned my own particular
semantics to those attributes.

If the web is to continue to encourage distributed invention, the
publication of a new specification cannot retroactively change the
meaning of all of my content.

Given that there are mechanisms that allow the author to make
assertions about the intended semantics, I don't see how or why the TF
should assert a retroactive change.

With respect to RDFa in XHTML, I suppose the fact that this document
is a work product of teh XHTML WG, means that you can, if you insist,
assert that you're changing the meaning of XHTML and you're taking
away my ability to use the extensions I was using by giving them a
standard meaning.

Of course, if that's what you're doing, this document should be folded
into a new XHTML specification, not published independently unless you
also provide a mechanism for me to assert allegiance to this
specification from my XHTML documents...

To the extent that you think authors might wish to use RDFa in other
flavors of HTML, I don't think you have that latitude. You have no
authority to assert that @about or @property in a plain-old-HTML
document have any particular meaning unless you use @profile or some
other hook to allow the author to establish that link.

| However, you are quite right that technically, since HTML took the
| approach that unknown attributes should be ignored, it's possible that
| our author could be using @about and @property in some other way, so
| we should look at that.
|
| The safest approach to take, to protect those authors, would be to
| continue to ignore the attributes. However, that would mean that we
| can never extend HTML or XHTML. It's probably too late for that,
| anyway, since we're already on version 4.01 of HTML; no current
| browser insists on the presence of DTDs before it processes 4.01, so
| all of the attributes that are in 4.01 that weren't in version 3
| should by rights not be processed unless the DTD is present. I think
| we need to accept that in all modern browsers the processing/rendering
| part is independent of the validation part, and so trying to protect
| attributes from future processing rules is nigh on impossible.

As I said above, if the HTML WG publishes a new specification for
HTML, then that changes the rules for HTML. With respect to the
semantics of the elements, I wish they'd give me some way to indicate
what version I authored against (aside from the DTD), but that's a
(barely) separate question.

| But we should note, too, that the HTML spec never guaranteed that you
| could safely use your own made-up attributes for ever, anyway.

Indeed. HTML can change, I must have understood that. But it never
warned me that I had to read every single spec published by all of the
standards orgs in case one of the decided to impose new meaning on
attributes in HTML.

| It's true that the HTML spec says that a processor should ignore
| unknown attributes, but that was meant to be a sensible alternative to
| simply bailing out with an 'unknown attribute' error. The 'ignore the
| attributes' part of HTML was certainly never regarded as a way to
| allow authors to simply make up their own attributes--in fact, there
| is nothing in the spec that says the attributes should even be
| reflected in the DOM. In short, our author who is using attributes in
| some 'custom' way is on shakey ground, since the attribute could at
| any point be used in a new version of the language. (Which is, of
| course, why many of the modern Ajax libraries either use @class, or
| their own namespace qualified attributes, when adding new features.)

Yes, I'd have been entirely happy if you'd used rdfa:about and
rdfa:property, but I won't even try to go there...

[...]
| So, to recap, although many people in the discussions were sympathetic
| to the argument--and indeed many argued for exactly this position for
| quite a long time!--the conclusion was that we didn't actually need to
| be so prescriptive, and there was benefit to not being so.

*Shrug*

I can't argue that there's a short-term benefit to the approach you've
elected to take. And the risk that you'll do serious harm to anyone is
miniscule (though I assert non-zero).

I remain concerned that you are setting a precedent that will have
negative consequences in the long-term. By divorcing RDFa from the
"follow your nose" principle, you're necessarily requiring users to be
in posession of "out of band" knowledge in order to understand your
documents. If everyone does this, I think one of the real benefits of
the web will be lost.

I guess part of the problem is that I don't see *any* reason not to
provide some sort of explicit markup in the document to signal that
it makes use of RDFa semantics.

| But even if the argument is made again for insisting on the presence
| of some indicator, before we know for certain that the author is not
| using @about and @property in some private way, @profile is definitely
| not the answer (as I've written about before).

I gather that the TF has worked through this and come to deliberate
conclusions. I'm not happy with the result, but given that you are the
XHTML WG and you're changing the meaning of XHTML, I don't think I'd
be doing the world any favors if I decided to lie down in the road
over it.

If you weren't the XHTML WG, I don't think you'd have a technical leg
to stand on and I'd be a lot more obstinant. If you expect RDFa to be
used in plain-old-HTML, I think you should reconsider your position.

                                        Be seeing you,
                                          norm

-- 
Norman Walsh <ndw@nwalsh.com> | Convictions are more dangerous enemies
http://nwalsh.com/            | of truth than lies.-- Nietzsche

Received on Monday, 3 March 2008 21:56:11 UTC

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