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"Alaric B. Snell" wrote:
> It's not a DAG; you can't share subtrees. It's a tree!
[also doing too much attention-getting hand waving, I'm afraid, but anyway:]
The XML instance is neither a tree nor a directed acyclic graph. That's the
inherent point of XML as UnicodeWithAngleBrackets. You can instantiate the
output of a parse of that instance as a tree, a DAG, a full grove or any of many
arboretical forms. Parsers which presume a single particular form of concrete
instantiation following the parse of syntax are really parsers plus XML
processors. Such bundled processors first go astray in assuming that there
somehow inheres in the XML instance a model intended by the creator which must
be faithfully instantiated by the recipient. In narrow, particular applications
of XML this is in fact the premise. In the general case, however, the parse a)
verifies that the instance as received is properly XML and b) provides its
output as suitable input to a particular local processor which as its first task
must instantiate a data structure suited to the local use of the XML instance.
Gavin has said it in a succinct form which is hard to improve on (perhaps even
as a sutra defining the nature of XML):
***The generic XML processor is a myth once you get past the syntax.***
Respectfully,
Walter Pery
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