[wfs-dev] null values
John Herring
john.herring at oracle.com
Fri Oct 27 10:52:55 EDT 2006
Bart,
I have a problem with "nillable". See XML Schema,
Part 1, Section 3.3.3, bullet 2.2 at
http://www.w3.org/TR/xmlschema11-1/#d0e5913
If I am reading this right, if you use a "ref" (a
global element specification) to specify a subelement of a
type in a schema, then "nillable" cannot be used, and your
only shot at NULL versus NOT NULL is "minOccurs=0". Which
means that any concept of a nillable subelement of a feature
must be included in any global definition of the original
element, not specified differently for different uses.
That sounds a little off, and consideration the
times we naturally use ref in application schemas, a bit
dangerous.
Regards,
John
You do what you can when you can because you can.
The opinions expressed in this email are purely my own and
do not necessarily represent the opinions of any
organization
or otherwise sane person or persons.
John R. Herring
Architect, Spatial Products
Oracle Corporation
One Oracle Drive
Nashua, New Hampshire 03062
ph: 1 603 897 3216
fx: 1 603 897 3334
Annue cœptis - Novus Ordo Seclorum
-----Original Message-----
From: Bart van den Eijnden (OSGIS) [mailto:bartvde at osgis.nl]
Sent: Friday, October 27, 2006 10:31 AM
To: John Herring; 'Bart van den Eijnden OSGIS';
wfs-dev at opengeospatial.org
Subject: RE: [wfs-dev] null values
Hi John,
I think XMLSchema deals with this by having the minOccurs as
well as the nillable attribute on an element.
So minOccurs="1" nillable="false" would mean NOT NULL.
Best regards,
Bart
--
Bart van den Eijnden
OSGIS, Open Source GIS
http://www.osgis.nl
--------- Oorspronkelijk bericht --------
Van: John Herring <john.herring at oracle.com>
Naar: 'Bart van den Eijnden OSGIS' <bartvde at osgis.nl>,
wfs-dev at opengeospatial.org <wfs-dev at opengeospatial.org>
Onderwerp: RE: [wfs-dev] null values
Datum: 27/10/06 11:36
> Bart,
>
> Most systems have their own way of dealing with
NULLs. In XML is
> seems to be simply leaving out the element.
> Which leads to an interesting philosophic question about
your
> proposal.
>
> If one writes:
>
> <MYFIRSTITEM>aaa</MYFIRSTITEM>
> <PRIORITY/>
> <MYTHIRDITEM>zzz</MYTHIRDITEM>
>
> And the original schema calls for PRIORITY's
minOccurs to be 1, have
> you violated the intent of the schema? In SQL you get to
put in
> "NOT NULL" and in XML you get to put in
> "minOccurs=1" and force a value. In either of
your
> suggestions with a PRIORITY element, you are not in
violation of a
> "minOccurs=1" but you are in violation of the
semantics of
> not allowing a NULL.
>
> Personally, I thing that IONIC is right and the only
way to do this
> is the way the XML gurus meant us to do it, which is with
minOccurs=0
> and missing elements. On the other hand, GML's multiple
flavors of
> NULL does something else altogether, but at least you can
force an
> application schema not to use it (the equivalent of a NOT
NULL).
>
> Regards,
> John
>
> You do what you can when you can because you can.
>
> The opinions expressed in this email are purely my own and
do not
> necessarily represent the opinions of any organization or
otherwise
> sane person or persons.
>
> John R. Herring
> Architect, Spatial Products
> Oracle Corporation
> One Oracle Drive
> Nashua, New Hampshire 03062
> ph: 1 603 897 3216
> fx: 1 603 897 3334
>
> Annue cœptis - Novus Ordo Seclorum
>
>
> -----Original Message-----
> From:
> wfs-dev-bounces+john.herring=oracle.com at opengeospatial.org
>
[mailto:wfs-dev-bounces+john.herring=oracle.com at opengeospati
> al.org] On Behalf Of Bart van den Eijnden (OSGIS)
> Sent: Friday, October 27, 2006 9:06 AM
> To: wfs-dev at opengeospatial.org
> Subject: [wfs-dev] null values
>
> Hi list,
>
> how is a WFS supposed to deal with null values?
>
> I can see 3 options (for instance an attribute named
> PRIORITY):
>
>
> 1) just output an empty element (I guess not the cleanest
approach
> since it cannot be distinguished from an empty
> string)
>
> <MYFIRSTITEM>aaa</MYFIRSTITEM>
> <PRIORITY></PRIORITY>
> <MYTHIRDITEM>zzz</MYTHIRDITEM>
>
> I think this is how Mapserver WFS operates.
>
>
> 2)
> Leave out the respective element in the reponse.
>
> <MYFIRSTITEM>aaa</MYFIRSTITEM>
> <MYTHIRDITEM>zzz</MYTHIRDITEM>
>
> This is what Ionic WFS does.
>
> 3)
> An option I have not yet seen, output
xsi:nil="true" for the
> respective element?
>
> <MYFIRSTITEM>aaa</MYFIRSTITEM>
> <PRIORITY xsi:nil="true"></PRIORITY>
> <MYTHIRDITEM>zzz</MYTHIRDITEM>
>
> Ofcourse the 1) and 3) behaviour is easier to process (for
instance
> with
> XSLT) than the second one.
>
> Should the WFS spec say something about this? Or is it up
to the
> vendor? It would make life easier if they all did the same
thing IMHO.
> And I guess 3) is the cleanest approach.
>
> Thanks in advance for any input on this.
>
> Best regards,
> Bart
>
> --
> Bart van den Eijnden
> OSGIS, Open Source GIS
> http://www.osgis.nl
>
>
>
>
>
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