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Re: Fw: New Catalog XML Draft



# > Internal DTD rules override external DTD rules, but you can have both in
# > the same document. Internal DTD declarations come after the external DTD
# > call and between square brackets.

The following clarification may not be relevant for your work, but
just in case: The internal DTD is physically after the external DTD
reference in the XML document, but the internal DTD is processed
first. Strictly speaking, it does not override (i.e., redefine)
external definitions but rather declares them first and thereby
forbids the external DTD from declaring them. Therefore, you cannot
use the internal DTD as a way to modify elements defined in the
external DTD--you can only extend it by defining new elements.

The most error-prone part of the OGC Web Map Service metadata XML is
the provision for vendor-specific elements via a required but usually
empty %ENTITY declaration in the internal DTD. I have not yet
determined whether XML Schema will let us do this more effectively.

-Jeff DLB



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