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What is the relationship between XML namespaces and the XML 1.0 recommendation?
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63. What is the relationship between XML namespaces and the XML 1.0 recommendation?
Although the XML 1.0 recommendation anticipated the need for XML namespaces by noting that element type and attribute names should not include colons, it did not actually support XML namespaces. Thus, XML namespaces are layered on top of XML 1.0. In particular, any XML document that uses XML namespaces is a legal XML 1.0 document and can be interpreted as such in the absence of XML namespaces. For example, consider the following document:
<google:A xmlns:google="http://www.google.org/">
<google:B google:C="bar"/>
</google:A>
If this document is processed by a namespace-unaware processor, that processor will see two elements whose names are google:A and google:B. The google:A element has an attribute named xmlns:google and the google:B element has an attribute named google:C. On the other hand, a namespace-aware processor will see two elements with universal names {http://www.google.org}A and {http://www.google.org}B. The {http://www.google.org}A does not have any attributes; instead, it has a namespace declaration that maps the google prefix to the URI http://www.google.org. The {http://www.google.org}B element has an attribute named {http://www.google.org}C.
Needless to say, this has led to a certain amount of confusion. One area of confusion is the relationship between XML namespaces and validating XML documents against DTDs. This occurs because the XML namespaces recommendation did not describe how to use XML namespaces with DTDs. Fortunately, a similar situation does not occur with XML schema languages, as all of these support XML namespaces.
The other main area of confusion is in recommendations and specifications such as DOM and SAX whose first version predates the XML namespaces recommendation. Although these have since been updated to include XML namespace support, the solutions have not always been pretty due to backwards compatibility requirements. All recommendations in the XML family now support XML namespaces.
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