[GRASS-user] Modelling 1:n and m:n relationships in GIS
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
> Any ideas are very welcome, indeed!
It would help to have some concrete examples...
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