Re: [xml-dev] In converting XML instance A to XML instance B, thisproper

On Fri, Nov 29, 2013 at 12:02 PM, Steve Newcomb <srn@coolheads.com> wrote:

Semantics are in the mind of the author, and they are in the mind of the
recipient. They are never in data, no matter how encoded.
Moreover, the only realities that matter are the ones in our heads,
because those are the only ones upon which we can act.

Communication is possible only because we believe it is possible. We
believe it happens only because we have believed it long enough to
accumulate sufficient context with our correspondents to confirm us in
our belief. It's a matter of preponderance of evidence.
Disappointments -- i.e., communications failures -- are inevitable.

Parenthetically, I feel I must mention, at least in this xml-dev
context, the fact that same question was uppermost the minds of those
who insisted, many years ago, that every SGML document must have a DTD.

I know you know better than to conflate the presence of a Document Type Description with the presence of a DOCTYPE declaration. :-)

* Did the transmission conform?

* Did the recipient's process work correctly?

* Should the transmitter have known better than to transmit?

* 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. If Alice claims to send an XHTML document to Bob, then even if he validates it successfully, he has no guarantees that it is not actually a valid TEI document.

The XML Schema / RELAX NG model of validation, in which the schema is both logically and physically outside the document, avoids this problem. In that case, Bob will validate the document against his own XHTML schema, which will tell him not only whether the document is valid, but whether it is valid XHTML. The xsi:schemaLocation attribute and the xml-model PI reintroduce the problem, but in a way that is explicitly ignorable; DOCTYPEs are only partly ignorable, and only when not validating. (Per contra, the use of XML catalogs with DTDs partially mitigates the problem.)

This takes
some rather unsettling self-training, perhaps because our brains are
designed to ignore the latter and "pay no attention to the man behind
the curtain." The man behind the curtain is the rhetorician in the
room, and, like the Wizard of Oz, even *he* doesn't know how it works.

Unless he is a Phaedrus or a Northrop Frye.

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