null values in GML

[Steve Lime]

I guess we need a standard definition of NULL for all drivers then since
I don't believe it's
the same across the board. A mapserver-dev topic. Since we use char *
for all attributes
we could literally use NULL.

Also, often a schema will require an element, what to do with NULLs in
that case?

Steve

>>> "Bart van den Eijnden (OSGIS)" <bartvde at osgis.nl> 12/6/2006 1:07:55
PM >>>
Hi Steve,

as I understand from previous discussions on wfs-dev, it would be best

for Mapserver to leave out the attribute from the GML response in case

it's null.

For reference, check the threads named "null values" here:

http://mail.opengeospatial.org/pipermail/wfs-dev/2006-October/ 

although they get a bit hard to understand .... at least for me ....
:-)

Best regards,
Bart

Steve Lime schreef:
> Mateusz is most likely correct. MapServer extracts attributes and
> converts when necessary (not very often). If the asterix 
> always represents NULL then we could represent as something else
(empty
> string?) in the DBF code. What does GDAL/OGR
> do with NULLs in its output?
>
> Steve
>
>   
>>>> Mateusz Loskot <mateusz at LOSKOT.NET> 12/6/2006 9:44:29 AM >>>
>>>>         
> Bart van den Eijnden (OSGIS) wrote:
>   
>> Hi list,
>>
>> I have a strange phenomenon.
>>
>> A shape attribute table has some null values in it (column type
>> Real), for instance:
>>
>> OGRFeature(nap_speciaal):856 pnt_pntid (String) = 000A2510 .. 
>> hgt_hgtwd (Real) = (null) .. POINT (122880 487860)
>>
>> Using Mapserver WFS I get the following GML output:
>>
>> <ms:pnt_pntid>000A2510</ms:pnt_pntid> .. 
>> <ms:hgt_hgtwd>************************</ms:hgt_hgtwd> ..
>>
>> Does anybody have an idea what is causing the sequence of
asterisks?
>>     
>
> Asterix is used to indicate NULL value in Shapefile attribute.
> I'm completely not sure, but I suppose MS WFS driver does not handle
> asterix as null but accepts it as a string value and puts into
output
> GML.
>
> Cheers
>   


-- 
Bart van den Eijnden
OSGIS, Open Source GIS
bartvde at osgis.nl 
http://www.osgis.nl