[postgis-users] questions about geometry_columns base table!

[Obe, Regina]

1) Table _catalog menat to hold the database name, but in most cases
postgis just leaves that blank since there is a geometry_columns table
per database.  I'm not quite sure if the specs require that be filled in
though.  In theory it should since the standard ANSI SQL
information_schema tables require it filled in.
 
2) Well as you may have noticed - Postgis doesn't follow the MM Part 3
spec yet as for as these meta tables are concerned e.g. they don't start
with ST_ yet and geometry_columns is a physical table.  I haven't taken
that close a look at the specs to see if they really
require SRS_Name be the primary key.  Are you sure that is the case.
Most systems I know of based on my limited understanding key off of the
SRS_SRID.
 
Having the SRS_NAME be unique however doesn't seem like a bad idea since
it would prevent equivalent spatial reference systems from having 2
different identities.
 
Hope that helps,
Regina

________________________________

From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
zhangmb
Sent: Wednesday, July 09, 2008 5:44 AM
To: postgis-users at postgis.refractions.net
Subject: [postgis-users] questions about geometry_columns base table!


Hello,I have some questions about SQL/MM part 3:spatial.
1. In the definition of st_geometry_columns base table, what is the
meaning of the TABLE_CATALOG and what it should store exactly? what is
the meaning of the unqualified schema name and the qualified identifier?
2. In the definition of st_spatial_reference_systems base table, why
using SRS_NAME as primary key as opposed to using SRS_SRID?
 
Thanks a lot!
 
--zhangmb


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