[sc34wg3] TMQL, State of Affairs

[Jan Algermissen]

On May 24, 2005, at 8:01 PM, Martin Bryan wrote:
>

> explain why TMDM is so radically different from every other
> data model in the universe

Dunno what the significance of 'radically' is here. When data models  
are different
they are different, eh? So the QL of data model A does not work for  
data model B.

IMHO it is the natural way to go to define a new QL if you define a  
new data model.
The burdon to provide a 'mapping' of a given QL of datamodel A to  
data model B is
on the one who argues against the neccessity of a new QL...I'd say.

Example:

SELECT a1,a2,a3 FROM r WHERE a1 = 'foo'

is the SQL 'version' of the application of the relational operators  
RESTRICT and EXPAND
to r. (See Date's classic book for details on this)

If you can 'map' the rel algebra expression that underlies the given  
SQL statement to the
structural abstraction of data that TMDM provides, *then* you can  
apply the SQL statement to
TMDM instances. But only then.

Jan

> that it needs its own query language. My point of
> view is that if it can be expressed in XML it can be queried using  
> XQuery,
> and if it can be stored in a relational database it can be queried  
> using
> SQL. If your statement implies that this model cannot be properly  
> expressed
> in XML or stored in a relational database then people have a right  
> to know.
> If your statement does not imply this then explain why using the model
> introduces efficiencies. Don't, please, expect others to understand  
> this
> implicitly.
>
> Martin
>
>
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Jan Algermissen
jalgermissen@topicmapping.com