XML queries

Hi all!

Reading deeper the proposal by Vivien about the XML queries, I've
noticed lots of possibilities we'll have with this system.

> The XML query will contain an understandable version of
> what the client wants to do (an XML version of sentenses like "put some values
> in that table", "create a new table", "set the reading permission for this user
> on that table", "give me the list of shoes for which the sale price is higher
> than the average sale price of the blue shoes",...)
> When the client wants to send a query, it will have to build the query, then
> get a string version of it (which can be saved, etc), send it to the provider,
> and then discard it. There will be a Gda_Xmlquery object and a lib to help in
> the job of creating (,...) the query.
> Each provider will then have to get the XML string of the query, build back the
> corresponding Gda_Xmlquery object, convert it to an understandable query for
> the RDBMS it represents, send the query to the RDBMS, discard the Gda_Xmlquery
> object and return the result of the query to the client.
all this will go to the gda-common lib, so that using this on
clients/providers will be very easy!

> * I hope that in the future, the client will be able to ask the provider to
> give him the XML Queries to save the structure and the data of a database (in
> the way gda-xml lib does now, but with more accuracy).
yes! this could be added to the schemas maybe... as we do with the SQL
command, we could ask for the XML string needed to build that object.
This would make the import/export tools very easy to implement.

> * It will be possible to ask the provider for an equivalent, in the language
> its RDBMS use, of the XML query to give some feedback to the user of the 
> client.
that's perfect, for importing data exported on a different DBMS

> This query specification allows to ask for only the SELECT, DELETE, INSERT and
> UPDATE operations for now, but has the possibility to be extended for CREATE
this should be very easy, as soon as we've got the basic commands
working. I think the most difficult of all these is the SELECT command.

The DTD format, in my opinion, fits very well with CÚdric's ideas, don't
you think?

BTW, I'm putting this proposal on the web site.


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