This is the archive of the goodrelations dicussion list

Dear all:

When using RDFa mark-up in HTML/XHTML documents, there is a nasty 
pitfall regarding empty elements.

Do NOT use the popular shortcuts known from XML for empty elements in 
RDFa markup.

I.e., instead of

<span/>

ALWAYS use the long form

<span></span>

This hold for all elements that contain RDFa attributes.
*
Background:*

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>.

Earlier versions of HTML and many HTML documents in the wild were not 
well-formed, i.e., they often did not close elements properly.
This caused the browser industry to employ tricks for dealing with 
inconsistent markup.

Now, if you are using RDFa in an XHTML document, the shortcut can cause 
problems depending on the media-type indicated by your server.
- If the media-type is XML, many modern browsers have no problem.
- However, if the XHTML page is served as HTML, many browsers apply 
heuristics that unfortunately turn the RDFa markup inconsistent.
- 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.

Thus, avoid the shortcut for empty elements in RDFa markup.

See the following document for background info:

http://tr.im/z8f1

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.

Best wishes

Martin Hepp

-- 
--------------------------------------------------------------
martin hepp
e-business & web science research group
universitaet der bundeswehr muenchen

e-mail:  mhepp at 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 GoodRelations for E-Commerce on the Web of Linked Data!
=================================================================

Webcast:
http://www.heppnetz.de/projects/goodrelations/webcast/

Recipe for Yahoo SearcMonkey:
http://tr.im/rAbN

Talk at the Semantic Technology Conference 2009: 
"Semantic Web-based E-Commerce: The GoodRelations Ontology"
http://tinyurl.com/semtech-hepp

Overview article on Semantic Universe:
http://tinyurl.com/goodrelations-universe

Project page:
http://purl.org/goodrelations/

Resources for developers:
http://www.ebusiness-unibw.org/wiki/GoodRelations

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 
http://tr.im/grcec09

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