[whatwg] Trying to work out the problems solved by RDFa
Calogero Alex Baldacchino
alex.baldacchino at email.it
Sun Jan 11 08:52:40 PST 2009
Benjamin Hawkes-Lewis ha scritto:
> On 11/1/09 02:51, Calogero Alex Baldacchino wrote:
>> eRDF might be a working compromise, because it doesn't need any changes
>> to the spec
>
> It's not possible to author conforming HTML5 that functions as eRDF
> since eRDF requires a 'profile' attribute, but HTML5 has removed the
> attribute.
>
I didn't noticed that before, thanks for the info :-)
However, actually it's the same for RDFa attributes, because they're not
in the spec. From this point of view, introducing six new attributes, or
resorting to an older one is not very different, thus (again) why RDFa
and not eRDF? Or why not both? Or not also RDFa embedded in Atom
embedded, in turn, in HTML (like SVG or MathML)? It seems to me, for
instance, that at this stage SearchMonkey might be a reason to consider
all of them.
>
> ; RDFa covers a wider range of RDF semantics, but requires
>> new attributes and also namespaces (a sort of hybrid beteween them might
>> avoid the need to bring namespaces - xmlns:* attributes - into html
>> serialization).
>
> To avoid xmlns:* attributes, one could drop CURIEs in the text/html
> serialization and use markup like:
>
> <div>
> <div about="http://dbpedia.org/resource/Albert_Einstein">
> ...
> </div>
> </div>
>
> instead of
>
> <div xmlns:db="http://dbpedia.org/">
> <div about="[db:resource/Albert_Einstein]">
> ...
> </div>
> </div>
>
> There's no data loss.
>
Well, that's a chance, of course, but that's *not* RDFa as specified by
W3C; for instance, @property is specified as accepting _only_ CURIEs
(whereas @about can accept also URIs - and eRDF allows curies, even if
in a different format than what specified for RDFa and what is used for
XML in general). That is, to do that not one, but _two_ specifications
need to be changed, current HTML5 (which is a draft, thus not a
problem) and RDFa (which now is a Recommendation, thus, might it be more
difficoult? should a different specification be derived?), unless we
want that to be just an unofficial, yet widely accepted, convention -
and I think that an unofficial convention is worth the others (any
processors conforming to standard RDFa would need deep changes to cope
with that - it doesn't work in Fuzzbot when CURIEs are expected, for
instance). I'm the first to say that my suggestion was an ugly hack, but
at least it would have been working and conformant without changing
anything.
>> My suggestion was meant as a mean to test RDFa in HTML
>> documents without changing the spec (perhaps in conjunction with
>> data-xmlns-*, data-xmlns-prefixes="rdfa foaf <whatever>" to "emulate"
>> namespaces - an ugly hack, I know, but at least would avoid changes to
>> html serialization, at least in a test phase) -- even if I think that
>> xml serialization should work better for such rdf metadata.
>
> I really can't see anybody violating the spec in that way rather than
> violating the spec by just adding the RDFa attributes outright, --
Indeed, current specs are violated, and I was just considering a way to
use RDFa without such violations before deciding if it's worth to be
added to the spec, no more (and I don't want to push that hack anymore,
just trying to point out my aim).
> --especially given that there are already people publishing these
> attributes in text/html so the "namespace" has already been polluted
> and we already have services like SearchMonkey not only using these
> attributes but promoting them.
It seems to me that SearchMontky doesn't promote RDFa more than it
promotes Microformats, eRDF and dataRSS (RDFa embedded in external Atom
feeds). It's also a very recent feature, and I really can't guess which
kind of RDF serialization is going to "win the battle" (that is,
choosing one against the others *might* be a premature choice right now,
as well as introducing all of them).
> It may therefore already be problematic for a future version of HTML
> to use these attributes as extension points without breaking existing
> sites. The "test" is already in progress, for better or worse. HTML5
> conformance checkers don't have to bless this test, of course, any
> more than CSS validators have to give the all clear to vendor-specific
> properties.
It's the same with every possible existing custom (non-standard)
attributes and elements out there, since there is no standard for them,
and instead data-* has been created; it's also the same for accesskey,
actually, since it's not in current spec (whereas it was in HTML4).
After all, support for unknown attributes/elements has never been a
standard "de jure", but more of a quirk, and there are no grants it will
work fine in the future (as well as actually it doesn't work
consistently for unknown elements cross-browsers -- there are strong
differences between IE and other browsers with this respect).
Moreover, the use of such attributes /for the purposes of SearchMonkey/
is a very, very custom use case, since they're used just for server-side
computations, thus no collaboration is required by other UAs; if
browsers just ignored and dropped such attributes (as they do with
unknown, proprietary CSS extensions), no page would be broken, whereas
SearchMonkey would work as fine. Problems might arise if they were used
in different contexts (e.g. as CSS selectors - but dropping unknown CSS
rules is allowed by CSS spec), but who cares of them might just run a
regex tool to map them to a new, standard-compliant version (given that,
for instance, "data-rdfa-about", "rdfa:about" and "about" are in a
1-to-1 correspondence, thus such might be done very easily by UAs as a
quirk).
From this point of view, SearchMonkey might use its own custom dataset
and model without any changes to its functionalities (AIUI, the basic
format for RDF metadata in SearchMonkey is dataRSS). Since there are
standards for embedding RDF into (x)html documents, it just makes sense
to support them all for Yahoo.
>
> Moreover, the damage done by immediately breaking the principle that
> data-* should be for private use only and turning it into a
> distributed extension point may be worse than the alternatives.
>
> --
> Benjamin Hawkes-Lewis
I really don't see the problem if a *custom* convention became widely
accepted and reused by other people (given that my idea started from a
Charls McCathieNevile's mail presenting small-scale scenarios, such as
organizations' internal use and external interchange with other selected
organizations, as a main context for RDFa - and I've never said HTML
specification should even mention it, I was thinking to it just as an
unofficial convention to experiment with in such scenarios).
I really can't get, right now, why it should be different, for instance,
from the case of a freely reusable widget using a custom data model
based on private data-* attributes inserted by people in thousands of
websites (the widget with relitive metadata, I mean), then liked by
other people and reused in different contexts (the same data model based
on data-*, now), unless we agree this should be avoided, but I can't
guess how to prevent people from reusing a "private-only" data model
they happened to like (unless it resulted in a copyright infringment,
but I'm not sure this may happen because of the mere use of the same
name for some "variables" elaborated by a similar script, yet different
in source code -- given that copyright is evaluated at source code
level, not per the resulting functionalities, as far as I know).
WBR, Alex
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