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What does the URI used as an XML namespace name point to?
XML Interview Questions and Answers
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118. What does the URI used as an XML namespace name point to?
The URI used as an XML namespace name is simply an identifier. It is not guaranteed to point to anything and, in general, it is a bad idea to assume that it does. This point causes a lot of confusion, so we'll repeat it here:
URIs USED AS XML NAMESPACE NAMES ARE JUST IDENTIFIERS. THEY ARE NOT GUARANTEED TO POINT TO ANYTHING.
While this might be confusing when URLs are used as namespace names, it is obvious when other types of URIs are used as namespace names. For example, the following namespace declaration uses an ISBN URN:
xmlns:xbe="urn:ISBN:0-7897-2504-5"
and the following namespace declaration uses a UUID URN:
xmlns:foo="urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6"
Clearly, neither namespace name points to anything on the Web.
NOTE: Namespace URIs that are URLs may point to RDDL documents, although this does not appear to be widely implemented. For details, see the next question.
NOTE: An early version of the W3C's XML Schemas used namespace URIs to point to an XML Schema document containing the definitions of the element types and attributes named in the namespace. However, this proved very controversial and the idea has been withdrawn.
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