HTML and CSS Reference
Listing 7-87. A Long List of Namespaces in an XHTML+RDFa Document
<html version="XHTML+RDFa 1.0" xmlns=" http://www.w3.org/1999/xhtml "
xmlns:dbp=" http://dbpedia.org/property/ "
xmlns:dbr=" http://dbpedia.org/resource/ "
xmlns:geo=" http://www.w3.org/2003/01/geo/wgs84_pos# "
xmlns:owl=" http://www.w3.org/2002/07/owl# "
xmlns:rel=" http://vocab.org/relationship/ "
xmlns:rss=" http://web.resource.org/rss/1.0/ "
xmlns:vcard=" http://www.w3.org/2006/vcard/ns# "
These vocabulary prefixes allow the use of terms defined by the listed external vocabularies in the current
document. It is highly recommended to list only those namespaces that are actually used in the document, which
contributes to code optimality and easier maintenance. Although unnecessary namespaces do not cause any error
messages in the browser, they make the markup more complex.
Because of the different features of vocabularies, the combined application is not always straightforward.
For example, many terms are included in various vocabularies, and choosing one of them is often driven by personal
preference only. In fact, you should take the specification of the candidate properties into account in order to choose
the most suitable one for your scenario.
Combining Vocabularies in RDF
The easiest way to mix properties from any vocabulary is to create an RDF file. For example, a completely machine-
readable personal profile uses FOAF terms to describe the title, name, gender, IM accounts, home page, phone
number, and relationships of a person. The nearest airport to the office of the person can be expressed with a term
from the Contact vocabulary, the date when the file has been created can be declared by Dublin Core, and so on