Re: Help with complex db design concepts

paul_geoffrey_brown_at_yahoo.com (Paul G. Brown) wrote in message news:<57da7b56.0205091155.1f655f13_at_posting.google.com>...
> Why are you splitting the spatial objects up into so many tables? They're
> all just 'features' of the geographic landscape, and they can be
> labelled to reflect their type. What about the following schema?
>
> CREATE TABLE Geo_Features (
> Id System_Generated_Identity PRIMARY KEY,
> What Feature_Type NOT NULL,
> Where ST_Spatial_Type NOT NULL
> );
>

<snip>
> The spatial part of the problem is a bit of a red herring.

User defined datatypes, in general, and spatial, in particular, have their own caveats. It requires extra abilities from query writer. For example,

where a.contains(x) and b.contains(x)

is logically the same as

where intersects(a,b).contains(x)

but I doubt if there are optimisers today that know about this identity. Received on Sun May 26 2002 - 19:33:00 CEST