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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Xml is _not_ self describing
> - An XML document without any related DTD is not self-describing. It
merely
> transmit data about a labeled tree, there is no meta-data available. You
can
> check its well-formedness, but for that you just apply external
> well-formedness rules to the document.
> - An XML document with an embedded DTD is self-describing, for computer
that
> know about XML and DTDs, and for validation purposes. The document itself
> provides information on how it has to be processed to be declared valid in
> its own sense.
I've forgotten this :
- An XML document, with or without an associated DTD, tends to be
self-describing for the human eye, provided that the reader understand the
tag and attribute names (which may require a translation work). But then
again, the reader has a human intelligence, and still can be puzzled by some
bad designed XML documents ("I've got two <adress> elements in this
<invoice>. Which one is the billing address, and which one is the delivery
address ?"), or by its sheer complexity (imagine yourself trying to figure
out what a XSL/T stylesheet means without knowing about XSL/T and XPath.
Please, be honest :). Like someone briliantly wrote in this thread, the
meaning does not come from the XML, but from the natural language used in
the tag names. Yet, even for a human mind, XML documents that are truly
self-describing (no "holes", no ambiguity) are a rare thing.
> - However, outside the bounds of very precise algorithms (validation), an
> XML document with an embedded DTD is not self-describing for computers in
a
> more general processing context. Nothing tells the computer about how the
> data should be processed. The document has no control over its own fate.
An
> invoice document is not describing how it should be processed by an
> accounting system. The information comes from elsewhere.
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