[Mapserver-dev] Expressions

[Steve Lime]

EXPRESSION support is common across all contection types. That is,
expressions don't leverage connection specifics at all. This was done
for consistancy. Otherwise you'd have one set of expression rules for
shapefiles, another for PostGIS and so on. Moreover only a limited
number of connection types even have the capability to do SQL-like
stuff. FILTER on the other hand DOES allow for vendor specific attribute
filtering. So for SDE the FILTER amounts to a where clause. For
shapefiles FILTER uses the same syntax as EXPRESSION. The difference is
where in the process a FILTER is applied. Basically FILTERing happens
before feature geometry is read from a connection so there are
performance benefits. 

Again the expression code is neutral and is found in maputil.c,
mapparser.y and maplexer.l.

Steve

>>> attila at prometheus.org.yu 06/17/03 03:13AM >>>
I'm wondering which parts of the code make the EXPRESSION support for
certain 
connectiontypes ? I presume it's like filtering, but can't quite locate
it. 
On a side note - do all connectiontypes support expressions ?

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