Mark Birbeck wrote:
Hi Dan,
I want to express the foaf:sha1 property of an image in my homepage
(which already uses RDFa):
From http://danbri.org/
<img rel="foaf:depiction" src="danbri-txt.jpg"
alt="danbri" style="float: center"/>
...this was already there, saying the picture was a depiction of me.
@src acts like @about, not @resource/@href. So you would need to do this:
<span rel="foaf:depiction">
<img src="danbri-txt.jpg" alt="danbri" />
</span>
Ah. Was my original markup wrong then? Or just not extensible to this
new sha1 need
This is the kind of use-case that made it better to have @src
represent 'a subject' rather than an object. It means that you are now
able to do this:
<span rel="foaf:depiction">
<img src="danbri-txt.jpg" alt="danbri"
property="foaf:sha1sum" content="58d174f20c039289544b2364c5c21295df2e4a2b"
/>
</span>
Thanks. Homepage updated! I've also added jquery to my homepage, and the
hash for that specific jquery into the <head> using meta as you mention
below.
BTW can I jump in here before an example spreads further: the property
is foaf:sha1 not :sha1sum. We do have a mailbox identity property called
foaf:mbox_sha1sum but feedback was that this was a bit wordy, so when
foaf:sha1 was added we went the short route (yes, at the cost of
internal consistency...).
Here is the RDFa N3 I get from my homepage now, using the development js
parsing bookmarklet:
<http://danbri.org/jquery-1.2.3.min.js> <http://xmlns.com/foaf/0.1/sha1>
"6463e558dd79d51a2e8464806824c7bbc18c77fd"@en .
<http://danbri.org/> <http://www.w3.org/1999/xhtml/vocab#stylesheet>
<http://danbri.org/simple.css> .
<http://danbri.org/> <http://www.w3.org/1999/xhtml/vocab#meta>
<http://danbri.org/foaf.rdf> .
<http://danbri.org/> <http://www.w3.org/1999/xhtml/vocab#alternate> <
http://feeds.feedburner.com/danbri_blog?format=xml> .
_:n0 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<http://xmlns.com/foaf/0.1/Person> .
_:n0 <http://xmlns.com/foaf/0.1/weblog> <http://danbri.org/words/> .
_:n0 <http://xmlns.com/foaf/0.1/currentProject>
<http://www.foaf-project.org/> .
_:n0 <http://xmlns.com/foaf/0.1/currentProject> <http://widgetarians.org/> .
_:n0 <http://xmlns.com/foaf/0.1/depiction>
<http://danbri.org/danbri-txt.jpg> .
<http://danbri.org/danbri-txt.jpg> <http://xmlns.com/foaf/0.1/sha1>
"58d174f20c039289544b2364c5c21295df2e4a2b"@en .
Seems right :)
Douglas Crockford just posted a proposal for a hash= attribute in HTML,
to allow user agents to cache common files like jquery.js
http://blog.360.yahoo.com/blog-TBPekxc1dLNy5DOloPfzVvFIVOWMB0li?p=789
[...]
First, as we saw above this could already be implemented without
adding a new attribute, just by using RDFa.
Yes, that's rather nice huh? :)
RDF isn't always an agent of complication!
Second, by using RDFa we also get more flexibility in how this is
marked up. For example, we could just dump a whole load of hash values
into the head of our document:
<html>
<head>
<title>Dan's page</title>
<meta about="danbri-txt.jpg" property="foaf:sha1sum"
content="58d174f20c039289544b2364c5c21295df2e4a2b" />
</head>
I've done just that for jquery.
<script type="text/javascript" src="jquery-1.2.3.min.js"></script>
<meta about="jquery-1.2.3.min.js" property="foaf:sha1"
content="6463e558dd79d51a2e8464806824c7bbc18c77fd" />
Could I have done this instead?
<script type="text/javascript" src="jquery-1.2.3.min.js"
property="foaf:sha1"
content="6463e558dd79d51a2e8464806824c7bbc18c77fd"></script>
Or we could even load them from an external location. So the hash
values for particular scripts could be maintained by the script
publishers, for example. This means that the author need not even add
them--they could be added by a post-RDFa-parse phase.
Maybe they could be loaded and remembered from site-wide metadata but
that's a bit advanced (and not peculiar to RDFa; rdf/xml would work
there). Or perhaps I don't follow you.
Third--and this one is a bit more future-oriented--I explained in
answer to someone's question the other day about @cite, that certain
attributes nicely follow the @instanceof model, which is that an
attribute with a value represents a predicate and object pair. It's
pretty easy to see how this also works for @hash, which would be
equivalent to @property="xhv:hash". (It's a small point, I know.)
It's the same conceptual model, yup. Are you suggesting that in the
future, properties could be automatically generated for these?
ps. does anyone fancy hacking about in eg. Firefox to see about actually
implementing this? could be scary deep in the core code, but would be a
cool hack...
It's an interesting idea, but my feeling is that this step would
happen after the RDFa has been parsed, independent of how the URI was
marked with a hash value. So that would be the first step
We'd need to know more about when Firefox initiates requests for
dependent resources (css, js, images); if this is incremental, we'd need
RDFa parsing to be happening then too, otherwise waiting til page load
is complete could slow things down. But there we get into issue of
different behaviours between XHTML and HTML maybe, since XML needs a
full document to work on, not a stream...
cheers,
Dan
--
http://danbri.org/
