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Re: In converting XML instance A to XML instance B, thisproper

• From: Steve Newcomb <srn@coolheads.com>
• To: John Cowan <johnwcowan@gmail.com>
• Date: Sun, 01 Dec 2013 16:23:09 -0500

On 11/30/2013 02:34 PM, John Cowan wrote:

>     * Should the recipient have known better than to accept the
>     transmission?
> 
> 
> The point about the recipient isn't so clear to me.  When the recipient
> validates a document, that says exactly nothing about whether the
> document is usable to the recipient, because the declarations are *part*
> of the document.  This, I think, is the weakness of classical DTDs:
> there is no easy way to tell if the DOCTYPE attached to the document by
> the sender has anything to do with what the recipient expected to see.

Are you saying that the recipient can't test an included document type
definition for equivalence to the agreed-upon syntactic constraints?

This was actually a serious issue, at least in the HyTime committee,
before W3C dismissed architectural forms / meta-DTDs as "too ugly" and
then proceeded to promulgate the relative beauty of XML Namespaces
(sarcasm intended).

Inherent in the architectural forms idea was the notion that any schema
that was *more* constrained could be used in place of the agreed one,
but not one that was *less* constrained.  For a while, I personally
believed there needed to be a way to test whether that was true.  In the
end, though, for all purposes of standardization, at least, we decided
that only the instances mattered, and we could easily tell whether an
instance conformed to an agreement, or didn't.  It just didn't matter
what the source-system believed the schema was as long as its product
conformed to the agreement.