[Tdwg-tag] A very simple question stated again.

Blum, Stan sblum at calacademy.org
Mon Mar 27 09:45:23 CEST 2006

"Are the semantics encoded in the XML Schema or in the structure of the XML
instance documents that validate against that schema? Is it possible to
'understand' an instance document without reference to the schema?"

Possible answers are:

	1.	Yes: you can understand an XML instance document in the
absence of a schema it validates against i.e. just from the structure of the
elements and the namespaces used.
	2.	No: you require the XML Schema to understand the document. 


Roger, If you postulate that the instance document is valid against the
schema, and the that the element and attribute names are meaningful to the
reader (a human, or software written by a human who understands their
meaning), then the only additional semantics the schema could provide would
be in the annotations/documentation, if any exist in the schema.  

I'm not entirely sure what you include in [data] "structure", but if you only
mean concepts such as tuples, trees, sets, lists, bags, etc., then I would
disagree that semantics are encoded substantially in data structure (of the
XML instance doc or any other record).  It is true that without proper
structure, semantics cannot be encoded, but I think semantics are encoded
predominantly in class/element-attribute names and any referenced
documentation (i.e., natural language).  If you replace meaningful names with
surrogate keys (e.g., integers) and thereby obscure any meaning conveyed by
the names, then the instance document would lose a lot of its meaning.

I'm not exactly sure how this relates to the earlier discussion about XML
schema, RDF, and more powerful modeling methodologies like UML. but I hope it



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