Can I use XML namespaces in DTDs?

XML Interview Questions and Answers

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86. Can I use XML namespaces in DTDs?

Yes and no.
In particular, DTDs can contain qualified names but XML namespace declarations do not apply to DTDs .
This has a number of consequences. Because XML namespace declarations do not apply to DTDs:
1. There is no way to determine what XML namespace a prefix in a DTD points to. Which means...
2. Qualified names in a DTD cannot be mapped to universal names. Which means...
3. Element type and attribute declarations in a DTD are expressed in terms of qualified names, not universal names. Which means...
4. Validation cannot be redefined in terms of universal names as might be expected.
This situation has caused numerous complaints but, as XML namespaces are already a recommendation, is unlikely to change. The long term solution to this problem is an XML schema language: all of the proposed XML schema languages provide a mechanism by which the local name in an element type or attribute declaration can be associated with an XML namespace. This makes it possible to redefine validity in terms of universal names.

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Other Interview Questions

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• How are universal names represented?
• How will XML affect my document links?
• Can I use a relative URI as a namespace name?
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• When constructing an XML DTD, how do you create an external entity reference in an attribute value?
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• What is an XML namespace prefix?
• More...