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Hi All,<br>
<br>
Gregor posted my rather long winded description of confusion about
semantics in XML Schema to the list and it may have confused you. It
can be summed up with a simple question to which a simple answer is all
that suffices.<br>
<br>
<b>"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?"</b><br>
<br>
Possible answers are:<br>
<ol>
<li><b>Yes:</b> 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.<br>
</li>
<li><b>No</b>: you require the XML Schema to understand the document.</li>
</ol>
This is not a trivial question. The answers may require different
approaches to an overall architecture.<br>
<br>
Versioning of schemas, for example, becomes irrelevant if the answer is
Yes - as the meaning is implicit in the structure you can throw the
schema away and not loose anything. XML is 'self describing' so you
would think this must be true. The schema is just a useful device to
help you construct XML in the correct format.<br>
<br>
If the answer in No then we need clear statements about how all
instances must always bear links to a permanently retrievable schema -
or they become meaningless. We need very tight version control of
schemas and a method of linking between the versions so we can track
how the meaning has changed. We also need clear statements on what
happens when you can validate a document with multiple schemas? Does
this imply multiple meanings? Schemas must be archived with any data
etc.<br>
<br>
If you respond to this message please state a preference for either 1
or 2. There is no middle road on this one!<br>
<br>
All the best,<br>
<br>
Roger<br>
<pre class="moz-signature" cols="72">--
-------------------------------------
Roger Hyam
Technical Architect
Taxonomic Databases Working Group
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<a class="moz-txt-link-freetext" href="http://www.tdwg.org">http://www.tdwg.org</a>
<a class="moz-txt-link-abbreviated" href="mailto:roger@tdwg.org">roger@tdwg.org</a>
+44 1578 722782
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</pre>
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