Hi Tom:
Amen. Thank you for writing this. I completely agree. RDFa has some
great use cases but (like any technology) has its limitations. Let's
not oversell it.
We seem to agree on the observation, but not on the conclusion. What I
want and suggest is using RDFa also for exchanging a bit more complex
RDF models / data by simply using a lot of div / span or whatever
elements that represent the RDF part in the SAME document BUT NOT too
closely linked with the presentation level.
<body>
<h1>This is the car I want to sell</h1>
Actually, a pretty cool car, for only $1.000. Offer valid through July
31, 2009
<span>
... my whole RDF in RDFa
</span>
<body>
The advantage of that would be that
- you just have to maintain ONE file,
- data and metadata are close by, so the likelihood of being up to date
increases, and
- at the same time, the code does not get too messy.
- Also - no problems setting up the server (*).
- Easy to create on-line tools that generate RDFa snippets for simple
pasting.
- Yahoo and Google will most likely honor RDFa meta-data only.
Also note that often the literal values will be in content attributes
anyway, because the string for the presentation is not suitable as
meta-data content anyway (e.g. dates, country codes,...)
I think the approach sketched above would be a cheap and useful way of
publishing RDF meta-data. It could work with CMS / blogging software
etc. Imaging if we were able to allow eBay sellers to put GoodRelations
meta-data directly into the open XHTML part of their product description.
The main problem with my proposal is that there is the risk that Google
considers this "cloaking" and may remove respective resources from their
index (Mark raised that issue). If that risk was confirmed, we would
really have a problem. Imagine me selling Semantic Web markup as a step
beyond SEO ... and the first consequence of following my advice is being
removed from the Google index.
A second problem is that if the document contains nodes that have no
counterpart on the presentation level (e.g. intermediate nodes for
holding n-ary relations), then they will also not be dereferencable. The
same holds for URIs or nodes that are outside the scope of the actual
RDFa / XHTML document - I see no simple way of serving neither XHTML nor
RDF content for those.
Best
Martin
Tom Heath wrote:
Martin,
2009/6/27 Martin Hepp (UniBW) <martin.h...@ebusiness-unibw.org>:
So if this "hidden div / span" approach is not feasible, we got a problem.
The reason is that, as beautiful the idea is of using RDFa to make a) the
human-readable presentation and b) the machine-readable meta-data link to
the same literals, the problematic is it in reality once the structure of a)
and b) are very different.
For very simple property-value pairs, embedding RDFa markup is no problem.
But if you have a bit more complexity at the conceptual level and in
particular if there are significant differences to the structure of the
presentation (e.g. in terms of granularity, ordering of elements, etc.), it
gets very, very messy and hard to maintain.
Amen. Thank you for writing this. I completely agree. RDFa has some
great use cases but (like any technology) has its limitations. Let's
not oversell it.
Tom.
--
--------------------------------------------------------------
martin hepp
e-business & web science research group
universitaet der bundeswehr muenchen
e-mail: mh...@computer.org
phone: +49-(0)89-6004-4217
fax: +49-(0)89-6004-4620
www: http://www.unibw.de/ebusiness/ (group)
http://www.heppnetz.de/ (personal)
skype: mfhepp
twitter: mfhepp
Check out the GoodRelations vocabulary for E-Commerce on the Web of Data!
========================================================================
Webcast:
http://www.heppnetz.de/projects/goodrelations/webcast/
Talk at the Semantic Technology Conference 2009:
"Semantic Web-based E-Commerce: The GoodRelations Ontology"
http://tinyurl.com/semtech-hepp
Tool for registering your business:
http://www.ebusiness-unibw.org/tools/goodrelations-annotator/
Overview article on Semantic Universe:
http://tinyurl.com/goodrelations-universe
Project page and resources for developers:
http://purl.org/goodrelations/
Tutorial materials:
Tutorial at ESWC 2009: The Web of Data for E-Commerce in One Day: A Hands-on
Introduction to the GoodRelations Ontology, RDFa, and Yahoo! SearchMonkey
http://www.ebusiness-unibw.org/wiki/GoodRelations_Tutorial_ESWC2009
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