[TinyOWS-users] Should the feature attributes order in XML matter ?

[Jean-François Gigand]

Hi Gissur,

Interesting!
I use libxml2 2.7.8 on Debian.

I have spent quite some time check the WFS et XML schema specs.
I was surprised but this is the normal behaviour.

If you noticed a difference between two versions of libxml2, I would
guess that the new version is right and the older was too tolerant for
this sequence elements order issue.
Maybe a clue could be find in the libxml2 change log...


JF



2011/2/19 Gissur Þórhallsson <gissur at loftmyndir.is>:
> I suddenly started getting this message too.
> I'm not entirely sure what happened - I've had tinyOWS running without a
> hitch for a couple of months now and then all of a sudden I start to get
> "xml is not valid"
> And peeping into the logs gives me:
> [Sat Feb 19 12:42:34 2011] [ERROR] Element
> '{http://my.namespaceurl.com/}area': This element is not expected. Expected
> is one of ( {http://my.namespaceurl.com/}date_created,
> {http://my.namespaceurl.com/}date_modified,
> {http://my.namespaceurl.com/}username,
> {http://geoserver.loftmyndir.is/}origin ).
>
> Funnily enough this does not happen to all layers - simple layers (as in
> with few attributes, in my case only numeric area and a text field for
> comments) seem unaffected.
> I can't for the life of my figure out why this popped up all of sudden - the
> only thing I can relate this to is a system-wide upgrade I made on my box,
> which is running ubuntu 8.0.4. LTS box- and if I correlate my tinyows.logs
> with /var/log/apt/term.log I see that the "Expected is one of [...]" only
> start to appear around the time I upgraded libxml2 to  libxml2
> (2.6.31.dfsg-2ubuntu1.5) (I have no idea what version I was running before
> that).
> I'm going to see whether I can downgrade libxml2 and see if it changes
> anything.
> Or am I maybe barking up the completely wrong tree here?
> Kind regards,
> Gissur
>
>
> On Mon, Jan 31, 2011 at 10:05 PM, Jean-François Gigand
> <jean-francois at gigand.fr> wrote:
>>
>> Hi,
>>
>> For an 1.0.0 insert request, I get the exception "xml isn't valid"
>> with the following error:
>> [Mon Jan 31 21:11:05 2011] [ERROR] Element '{http://domain.net/}name':
>> This element is not expected. Expected is (
>> {http://domain.net/}deleted ).
>>
>> "name" and "deleted" are (among others) valid feature attributes.
>> If I change the attribute elements order in my test request XML file,
>> and follow exactly the PostgreSQL column order for that table, it
>> works.
>>
>> I am surprised. The WFS spec doesn't require a proper feature
>> attribute order in the list, does it?
>>
>> Having checked the w3schools doc about XML Schema, the <xs:sequence>
>> element requires the element order to be respected.
>> I see that validation is done by libxml2, and of course is done well.
>>
>> The problem, within the use cases of TinyOWS, is that PostgreSQL does
>> not provide any way to alter columns position.
>>
>> You would say that the app should anyway fetch the feature schema by
>> issuing a DescribeFeatureType request, and deal with the features
>> according to it...
>>
>> Actually, the OpenLayers serializer (exactly:
>> OpenLayers.Format.GML.Base.prototype.writers.feature._typeName)
>> creates the geometry first, then the attributes in object property
>> (for .. in).
>> If the geometry column in the PostgreSQL table is not the first (or
>> second after identifier), I could never insert any feature, and a
>> workaround with OpenLayers would be really messy.
>>
>> This would be an issue of OpenLayers of course. But I think it
>> wouldn't break the logic to add to the TinyOWS configuration an
>> optional "columns-order" attribute on the <layer> elements.
>> That attribute would contain the comma-separated list of columns to
>> export to the WFS client in the order they should be listed in the
>> DescribeFeatureType sequence.
>>
>> It would also allow to restrict the columns to export.
>>
>> What do you think?
>>
>> --
>> Jeff
>> _______________________________________________
>> TinyOWS-users mailing list
>> TinyOWS-users at lists.maptools.org
>> http://lists.maptools.org/mailman/listinfo/tinyows-users
>
>
>
> --
> Gissur Þórhallsson
>
> Loftmyndir ehf.
> Laugavegur 13
> IS 101 Reykjavík - Iceland
> sími (tel): (+354) 540 2500
> tölvupóstur (email): gissur at loftmyndir.is
>