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Re: [udig-users] Difference between Udig CQL & PostGIS SFSQL
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Hi Steven; I think you mean Common Query Lanague (CQL) if you found CFQ
somewhere it is a typo and we need to fix it!
Common Query Language is an OGC specification for performing really
simple queries (think of it as *just* the WHERE clause in SQL). We only
use it to offer a text friendly representation of what features are
selected on screen (or rows in a table if you prefer).
As for interaction with PostGIS we generate SFSQL requests as needed. We
generate these requests from all manner of things (CQL queries provided
by the user, the current viewport as the map is moved around, style
layer descriptor documents describing how to draw things on screen etc...).
As for the difference:
- SFSQL is used to access PostGIS
- CQL is used to show users a really limited query lanague because it
was fun to do!
The CQL format is defined as part of the OGC Catalog specification (in
much the same way as the WKT format is defined as part of the SFQL
specification)
- http://www.opengeospatial.org/standards/cat
When you make a new layer in uDig the attributes are not stored; it
directly talks to the spatial database. Indeed using uDig as a front end
for working with your spatial data base is a great way to get things
done. Some users have experimented with defining views in their database
and using uDig to look at the result. I actually would love to see a
"PostGIS console" made as a community plugin - perhaps after your report
you would be interested :-)
Thanks for the interesting question
Jody
Steven De Vriendt wrote:
Hi list,
I'm writing a report on the database connectivity of Udig and PostGIS
when both are used together.
I'm not sure on the hanlding of queries, however. I've looked up the
manual of Udig and it mentions
that CFQ is used as query language, while PostGIS makes use of SFSQL.
Can someone help
me to clarify the difference and why SFSQL isn't used in Udig ?
Last question. When I make a new layer in Udig, how are attributes
stored ?
Is it preferable to use Udig in combination with a (spatial) database ?
Thanks
Steven
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