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About external DTD

 
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Hi, these are from PXML2:


...an external DTD need not be a separate file - it could be stored as a record contained in a databse...


I don't know what it means, if this external DTD is stored as a record, how could we associate it with the internal subset?


...the external subset description of an element might allow several child elements, while the internal subset version specifies an empty element. Any XML data containing this DTD combination had better use an empty element, or it would be considered invalid.


Why does it say "it would be considered invalid"? The same element in the internal set can override the one in the external set, right? Pretty confusing.
Could anyone explain these to me? Thanks.
 
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I don't know what it means, if this external DTD is stored as a record, how could we associate it with the internal subset?
[Scratch my head] No idea how we could associate it with the internal subset in this case. No idea why would we store external DTD "as a record contained in a database" - maybe the authors mean "XML native database"... No idea how "need not be a separate file" relates to storing in a database - "files" and "database" are different animals, how to map "an entity" into files is database's inner implementation decision. Physically it may end up in different files.
Why does it say "it would be considered invalid"? The same element in the internal set can override the one in the external set, right? Pretty confusing.
They mean "an XML document would be considered invalid", not DTD. "The same element in the internal set can override the one in the external set" - this is correct, and because of this overriding now only empty content is valid.
 
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