[GRASS-user] Modelling 1:n and m:n relationships in GIS

Moritz Lennert mlennert at club.worldonline.be
Mon Mar 9 05:59:35 EDT 2009

On 09/03/09 00:00, Benjamin Ducke wrote:
> Dear all,
> I keep getting into situations where mapping 1:n and m:n relationships
> in relational DBMS to GIS vector models becomes a problem.
> The toughest restrictions of course are the 1:1 relation between map
> features and attribute table records

Where do you see a 1:1 restriction ? In GRASS you can have several 
features with the same category value, so related to one tuple in the 
table and you can have several category values for one feature, so 
related to several tuples in the table.

> and the fact that GIS relates
> data by spatial overlay, not foreign fields. I realize that some GIS
> (like GRASS) are somewhat more flexible in that they can attach more
> than one attribute table to a layer, but I am really looking for more
> portable ways to deal with this.
> - How do you deal with 1:n and m:n relations in GIS?
> - What do you do if there are no spatial representations for the
> records on the "n" side? Can that be handled at all?

Yes, the table you attach to your map can contain as many tuples as you 
want for which there are no features in the geometry. You can even 
attach a table to a map in which there is no tuple whatsoever related to 
a feature.

> Any ideas are very welcome, indeed!

It would help to have some concrete examples...


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