[DB-SIG] Re: [Pycon2005-attendees] Pycon2005 and database divide (ODB vs relational DB)

Patrick K. O'Brien pobrien at orbtech.com
Sun Mar 27 16:24:48 CEST 2005


Ian Bicking wrote:
> john.m.camara at comcast.net wrote:
> 
>> Do all databases need ad hoc query languages?
> 
> 
> A single language, no, but I do think they all need good support for ad
> hoc queries.  If I have to change my persistent data model to
> efficiently and consistently query the objects (or tuples) in a new way,
> then that model is too fragile.

One of the real conceptual challenges here is that queries in the
relational model are quite different from queries of objects.  In
relational, you have "dumb" data that you can pick apart and recombine
to form new sets of "dumb" data.  So a flexible language like SQL makes
sense.  With objects, I find it awkward to think about queries this way.

Schevo does have built-in methods that make it easy to find subsets of
objects, and those methods have some simple optimizations they apply
based on behind-the-scenes indexes that Schevo maintains.  And Schevo
automatically maintains bi-directional relationships between all
parent-child relationships and exposes access to this information in a
very simple and consistent API.  The combination of these two features
along with Python list comprehensions turns out to be extremely powerful
and flexible and works great for application code.

If I had to support completely ad-hoc end-user querying then I would
have someone write an ODBC driver so that a Schevo database looked like
a relational database to any ODBC client tool, like Access or Crystal
Reports.  Creating this ODBC driver is beyond my skill level as it will
involve a lot of nasty C code, but conceptually I'm confident it could
be done, since we can already easily export SQL from any Schevo database.

-- 
Patrick K. O'Brien
Orbtech    http://www.orbtech.com
Schevo     http://www.schevo.org
Pypersyst  http://www.pypersyst.org



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