[DAS2] Re: Apollo and DAS/2 priorities
dhoworth at mrc-lmb.cam.ac.uk
Mon Feb 6 14:27:34 UTC 2006
Andrew Dalke wrote:
> Dave Howorth:
>> Doing that automatically invalidates the document does it not?
>> "Definition: An XML document is valid if it has an associated document
>> type declaration and if the document complies with the constraints
>> expressed in it.
>> The document type declaration MUST appear before the first element in
>> the document."
> I think this page summarizes it nicely:
> "Valid" is a technical term referring to the presence
> of and conformance to a DOCTYPE declaration.
I think that's a paraphrase of the first para I quoted above?
> XML documents w/o a DTD are "well-formed". XML documents
> with a DTD and which agree with the DTD are "valid".
> In this case not being "valid" does not mean that the
> document is "invalid XML".
No, I believe you're wrong there; 'not valid' and 'invalid' have the
same meaning both colloquially and as used in the spec. It's either
valid or it isn't, and if it isn't then its invalid.
> As I understand things, it's perfectly fine to pass well-formed
> but not valid XML documents around.
I don't agree. There are occasions when it is acceptable but it's
generally bad practice, IMHO. The discussion in sec 5 of the spec gives
some motivation, particularly this section:
Or look here, or thousands of other places:
In particular for interoperability of an open, distributed system with
many writers and readers implemented by different groups (i.e. DAS), I
suggest validity is essential.
I would have expected your experience of the PDB to make you keen on
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