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Dear all:<br>
<br>
When using RDFa mark-up in HTML/XHTML documents, there is a nasty
pitfall regarding empty elements.<br>
<br>
Do NOT use the popular shortcuts known from XML for empty elements in
RDFa markup. <br>
<br>
I.e., instead of<br>
<br>
<span/> <br>
<br>
ALWAYS use the long form<br>
<br>
<span></span><br>
<br>
This hold for all elements that contain RDFa attributes.<br>
<b><br>
Background:</b><br>
<br>
In XML, it is okay to abbreviate empty elements by including a trailing
slash before closing the element, i.e. <span/> is the same as
<span></span>.<br>
<br>
Earlier versions of HTML and many HTML documents in the wild were not
well-formed, i.e., they often did not close elements properly.<br>
This caused the browser industry to employ tricks for dealing with
inconsistent markup. <br>
<br>
Now, if you are using RDFa in an XHTML document, the shortcut can cause
problems depending on the media-type indicated by your server. <br>
- If the media-type is XML, many modern browsers have no problem.<br>
- However, if the XHTML page is served as HTML, many browsers apply
heuristics that unfortunately turn the RDFa markup inconsistent.<br>
- Serving the document withj XML as a media type instead can in turn
create problems with old browsers, so that is not recommended either.
For many Web developers, the media type served is out of their control
anyway.
Many hosting packages always serve .html and .htm as HTML.<br>
<br>
Thus, avoid the shortcut for empty elements in RDFa markup.<br>
<br>
See the following document for background info:<br>
<br>
<a class="moz-txt-link-freetext" href="http://tr.im/z8f1">http://tr.im/z8f1</a><br>
<br>
Unfortunately, we have been using those shortcuts in some GoodRelations
recipes. As long as the markup is processed as XML, this works without
any problems. We will fix that in all recipes asap.<br>
<br>
Best wishes<br>
<br>
Martin Hepp<br>
<br>
<pre class="moz-signature" cols="72">--
--------------------------------------------------------------
martin hepp
e-business & web science research group
universitaet der bundeswehr muenchen
e-mail: <a class="moz-txt-link-abbreviated" href="mailto:mhepp@computer.org">mhepp@computer.org</a>
phone: +49-(0)89-6004-4217
fax: +49-(0)89-6004-4620
www: <a class="moz-txt-link-freetext" href="http://www.unibw.de/ebusiness/">http://www.unibw.de/ebusiness/</a> (group)
<a class="moz-txt-link-freetext" href="http://www.heppnetz.de/">http://www.heppnetz.de/</a> (personal)
skype: mfhepp
twitter: mfhepp
Check out GoodRelations for E-Commerce on the Web of Linked Data!
=================================================================
Webcast:
<a class="moz-txt-link-freetext" href="http://www.heppnetz.de/projects/goodrelations/webcast/">http://www.heppnetz.de/projects/goodrelations/webcast/</a>
Recipe for Yahoo SearcMonkey:
<a class="moz-txt-link-freetext" href="http://tr.im/rAbN">http://tr.im/rAbN</a>
Talk at the Semantic Technology Conference 2009:
"Semantic Web-based E-Commerce: The GoodRelations Ontology"
<a class="moz-txt-link-freetext" href="http://tinyurl.com/semtech-hepp">http://tinyurl.com/semtech-hepp</a>
Overview article on Semantic Universe:
<a class="moz-txt-link-freetext" href="http://tinyurl.com/goodrelations-universe">http://tinyurl.com/goodrelations-universe</a>
Project page:
<a class="moz-txt-link-freetext" href="http://purl.org/goodrelations/">http://purl.org/goodrelations/</a>
Resources for developers:
<a class="moz-txt-link-freetext" href="http://www.ebusiness-unibw.org/wiki/GoodRelations">http://www.ebusiness-unibw.org/wiki/GoodRelations</a>
Tutorial materials:
CEC'09 2009 Tutorial: The Web of Data for E-Commerce: A Hands-on Introduction to the GoodRelations Ontology, RDFa, and Yahoo! SearchMonkey
<a class="moz-txt-link-freetext" href="http://tr.im/grcec09">http://tr.im/grcec09</a>
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