PB138 — XML Namespaces

XML Namespaces (jmenné prostory)

XML Namespaces (W3C Recommendation, currently Namespaces in XML 1.0 (Third Edition) W3C Recommendation 8 Dec 2009): http://www.w3.org/TR/REC-xml-names
to new XML, there exists Namespaces in XML 1.1 W3C Recommendation (Second Edition) 16 August 2006. Andrew Layman, Richard Tobin, Tim Bray, Dave Hollander
They define logical spaces for names of elements, attributes in XML document.
They give the elements and attributes the "third dimension".
To each NS in XML, there is exactly one ("globally") unique identifier, given by URI (URIs is a superset of URLs).
NS corresponding to an URI does not anyhow relate to content that would potentially be available under the URL ("nothing is downloaded when processing NSs".

Prefixes and Equivalence of NSs (1)

Instead of URIs for denoting a namespace in document, one uses prefixes for these NS mapped to the respective URI using xmlns:prefix="URI".
Element- or attribute-name containing colon (:) is denoted as Qualified Name, QName.

Prefixes and Equivalence of NSs (2)

Two NS are equal iff their URIs are one-to-one-character the same (in UNICODE).
Namespaces do not apply to text nodes.
Element/attribute need not be in a namespace.

Prefixes and Equivalence of NSs (3)

NS prefix declaration or declaration or the implicit NS recursively applies to all descendants (child elements, their children etc.), unless another declaration "remaps" the given prefix.
One NS is co-called implicit (default) NS, declared by attribute xmlns=
Default NSs are NOT applied to attributes!!!, thus attributes without an explicit prefix do not belong to any NS.

Example 1. Default NS

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
  <body>
     <h1>Huraaaa</h1>
  </body>
</html>

Example 2. Prefixed NS

<xhtml:html xmlns:xhtml="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
  <xhtml:body>
     <xhtml:h1>Huraaaa</xhtml:h1>
  </xhtml:body>
</xhtml:html>

Issues related to NS

NS are not compatible with DTD.
DTD strictly differentiates between eg. name xi:include and include even if they belong to the same NS and should thus have the same interpretation/meaning for applications.