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

Trevor Wiens twiens at interbaun.com
Thu Sep 21 09:35:49 EDT 2006

On Wed, 20 Sep 2006 10:39:49 -0700
Dylan Beaudette wrote:

> > 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.
> 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?

As a very minor contributor to GRASS (contributing mostly to verbiage
on the lists rather than software), I'm not sure what insight I've
provided, other than my point of view. Some time ago when trying to
understand what 'layers' meant I raised the issue on the dev list and
others agreed with me that the terminology was confusing, but since it
was similar to the naming in OGR and Tiger files, no serious
consideration to renaming it was given. Further it was originally
named fields and then renamed to layers, which made the possibility of
renaming again more remote. Obviously 'link table' would have been a
reasonable choice. However it was and is my opinion that it would have
been simpler to simply allow for sql dynamic links for vector modules
and this allows much greater flexibility in the operation and supports a
superior SQL style of attribute management. I am extremely biased
however as someone who has done database application development for 15
years and uses PostgreSQL and PostGIS regularly.

Still, I do agree that the issue of the name is confusing and I don't
really care what terminology OGR or Tiger use, because to the average
user a layer is a single collection of vector or raster data. This term
is used this way in GIS textbooks and courses. If we actually care
about making inroads into the huge ESRI user base we need to make sure
that GRASS terminology is consistent and intuitive, otherwise the vast
majority of those users will never consider using GRASS. Let me be
clear on this, I don't suggest adopting ESRI terminology as their
terminology is often inconsistent and non-standard. However, in the
ESRI course discussion, the one point made over and over again is that
GRASS forces users to actually understand what they are doing rather
than clicking on buttons, thus it is not only a powerful analysis tool,
but also a pedagogical tool. This second role can only be effectively
fulfilled if the choice naming of features and modules is
logical, consistent, and intuitive. 

I also agree that this is something the GRASS steering committee needs
to seriously consider. If retained it needs a clear and obvious name,
not an ambiguous and confusing one. If not retained other work will
need to be done to support dynamic sql classication of features, which
now, may be more work, so is not likely to happen.

Trevor Wiens 
twiens at interbaun.com

The significant problems that we face cannot be solved at the same 
level of thinking we were at when we created them. 
(Albert Einstein)

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