[GRASS-user] RE: Problem querying layers other than '1' in gis.m

[Dylan Beaudette]

On Wednesday 20 September 2006 08:09, twiens wrote:
> ----- Original Message Follows -----
> From: Michael Barton <michael.barton at asu.edu>
> To: Moritz Lennert <mlennert at club.worldonline.be>, "Patton,
> Eric" <epatton at nrcan.gc.ca>
> Cc: "'grassuser at grass.itc.it'" <grassuser at grass.itc.it>
> Subject: Re: [GRASS-user] RE: Problem querying layers other
> than '1' in gis.m
> Date: Wed, 20 Sep 2006 07:48:43 -0700
>
> > You CAN link multiple tables to single vector objects.
> > That is what layers is all about. You need a separate CAT
> > column for each table you link. Each cat column is a
> > "layer". It serves as a key to link the object with a
> > record in a table.
> >
> > I don't know if v.what (used in gui vector querying) will
> > query more than layer one. There was some discussion about
> > this awhile back and I can't remember the outcome. There
> > have been some other new changes to v.what that will
> > eventually go into 6.3. If layer support has been added,
> > this will go into 6.3 also.
>
> v.what does not support layers.
>
> Eric,
>
> Your understanding of what layers are supposed to do is
> correct, they are multiple linked tables to a single
> topology layer, but there are unique cats for each linked
> table.
>
> Michael and Eric,
>
> I had been planning on adding support for multiple linked
> tables in v.what at some point, but since I deeply dislike
> the terminology and think the general approach to this
> problem is wrong in the first place I'm not motivated.
> Personally I think that attribute management should be left
> to the database backend and this so called feature should be
> dropped as the terminology is confusing. But.... there is
> deep resistance from a number of core developers who
> designed and implemented this multiple table link feature,
> so that is not likely to happen. The short and long of it
> however, is that there are other aspects of GRASS
> development which I'm more interested in and I think are
> more useful so that is where I have been and will be putting
> my limited time. If someone else wants to add "layers" to
> v.what that is fine, but I won't be doing it in the
> forseable future.
>
> T
> --
> Trevor Wiens
>
> --
> Trevor Wiens
> twiens at interbaun.com

Trevor,

thanks for the insight into some of the behind the scenes GRASS development. 
perhaps this would be a good topic for the steering committee to discuss? 
querying attributes (often from multiple linked tables) is an important tool, 
but if there is an underlying disagreement (with alternative data storage / 
terminology approaches) I am fairly sure that others would be interested in 
hearing about it, and possibly giving feedback (what do you think David 
S. ?).

Thoughts?

-- 
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341