Re: [xml-dev] The limitations of XPath and navigation for XML databasep

[Jonathan Robie <jonathan.robie@redhat.com>]

W. E. Perry wrote:
> Michael David prefers SQL precisely because in SQL one is
> manipulating semantic, not syntactic artifacts. 

Hi Walter,

How are you using the term "semantic" here?

To me, table names and column names are labels in the same way the 
elements and attributes are labels.

> He says as much in his
> example:
>
>   
>> For example a Department hierarchical structure can be hierarchically joined with an Employee hierarchical structure and processed using hierarchical views as in
>> SELECT Deptno, Empno FROM DeptView LEFT JOIN EmpView ON DeptID=EmpDeptID WHERE DeptNo=1204. This is a synergistic operation increasing
>> the semantic value of the combined queried structure beyond each structure queried separately and it can be processed interactively.
>>     

Both languages have joins. Both languages have ways of addressing data 
in the basic data model of the world they live in (tables vs. documents 
based on hierarchy and sequence). Both languages have ways of creating 
results in the basic data model of the world they live in (tables vs. 
documents).

Of course, XML is more complex than tables, and involves hierarchy and 
sequence.

>> Because the artifacts of an XML (and therefore
>> XPath) instance are purely syntactic--the A, B and C of Noah's example are
>> simply character text--Michael David assumes that they require some,
>> effectively procedural, processing to elaborate from each of them the
>> particular semantics which truly allow them to be declarative artifacts.

XQuery is actually defined in terms of a data model, not character text. 
That's why you can't address just a start tag or an end tag, for 
instance, or create XML that is not well-formed.

Beyond that, I'd like to define terms very carefully before discussing 
this in terms of semantic vs. syntactic, but you, Walter, know that 
about me ;->

Jonathan