[Qgis-developer] QEP/RFC sqlite virtual tables

[Régis Haubourg]

Hi all, 
this is a very high level topic for me. I will just point out some
user/funder needs, and maybe try to describe other strategies exist in GIS
softs. 

As a user coming from both ESRI and Mapinfo world:

 - The main (and last?) real advantage of MI was its native pseudo-SQL
capabilities (with many limitations). Users really often now have a
centralized spatialDB, where the administrator can do many things (almost
everything in fact), but the classical user has only two possibilies for
relation Db treatments: algorithms or duplicate data in sqlite and learn
spatial sql (unless their DBA grant them to Postgres... ). Power users are
very happy, ex MI users are not in QGIS. 

- Arcgis have no agregate capabilities over its relations.. Joins are more
developped and allow summarize algoithms. To go further, It requires using
an external DB system, and it's a pain (they all have limitations, in term
of cost or learning curve..). Postgis/sqlite is far away in terms of
accessibility

Having virtual sqlite tables would allow some MI-like behaviour. Users here
would appreciate that a lot (I will still be using postgres underneath for
perfs).
 For more simple use cases, some only want to improve joins by being able to
join and output agregate values if multiples tuples join, for simple mapping
purposes. I think UI needs boths things, a SQL dialog to create queries -
Qspatialite-like - on every table, and some agregate capabilities over
joins. 
 What we must avoid is having two different implementations, with differents
limitations. Only power users knowing what is really happening underneath
will know what function to use, which is bad in UX terms. 
A comparison is OGR CSV driver versus CSV plugin... User has to know that
both tools are differents, behaves differently with a different providers.
Nothing in the GUI let you know that except try-fail approach.

BTW, I have the feeling you don't disagree at all but that we are digging
one of the harder features of a GIS tool. IMHO, that really desserves
discussions, prooves of concept.  Any other opinions in dev's?


Cheers
Régis



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