[geos-devel] GEOS Exceptions

[Frank Warmerdam]

On 4/19/05, Artem Pavlenko <artem at pavlenko.uklinux.net> wrote:
> Hi Frank
> 
> I think EMPTY means literaly empty
> have a look at http://www.cl.cam.ac.uk/%7Emgk25/iso-14977.pdf

Artem, 

I have searched through this, and found nothing that says that EMPTY
is a special keyword in an EBNF grammar meaning nothing. 

In section 8.3 they have an EMPTY value, something like this:

PRIMARY
  = OPTIONAL SEQUENCE / REPEATED SEQUENCE
  / SPECIAL SEQUENCE / GROUPED SEQUENCE
  / META IDENTIFIER / TERMINAL / EMPTY.
EMPTY = .

This does not suggest to me that EMPTY is a real keyword you
can include in EBNF grammars with a specific predefined meaning. 

To be honest, I am a bit disgusted that this complication was left without
examples in the Simple Features for SQL specification. 

So, as I read the SFSQL spec, I am still left with the believe that 
an empty POINT should be expressed as "POINT EMPTY".  But
now I am inclined to halt my work on implementation till we have
broader agreement. 

Best regards,
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent