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Can anyone explain the purpose of the extra xsi_nil attributes that accompany a Web Feature Service (WFS) data source?

For example, when I create a WFS reader in FME for the topp:states demo layer of a stock GeoServer, the resulting table schema in my FME workspace includes extra attributes - one for each native attribute - named <attribute>_xsi_nil. Here's a screenshot highlighting the fields in question:

The data type for all of these xsi_nil fields is xml_boolean. This happens for all WFS layers I consume from a GeoServer.

What is the purpose of these extra fields?

And is there a way to configure the reader - or the GeoServer layer - to not cause these extra fields to be created?

Thanks

Not an answer but a continuation of this topic ...

After some more research, it's clear these extra fields are added when the fields are defined as nillable in the xsd schema:

0684Q00000ArKA4QAN.png

When I customize the xsd schema for this layer on the GeoServer, changing the nillable attributes to false, and then create a new WFS reader in FME, the extra xsi_nil fields are no longer present.

And after some research on the GML spec, I find that xsi_nil is an XML attribute used to indicate a nil value for an element instance, e.g.,:

<topp:SUB_REGION xsi_nil="true"></topp:SUB_REGION>

Is that the purpose for these extra fields in FME?  To accommodate the xsi_nil attribute setting?

Thanks

Not an answer but a continuation of this topic ...

After some more research, it's clear these extra fields are added when the fields are defined as nillable in the xsd schema:

0684Q00000ArKA4QAN.png

When I customize the xsd schema for this layer on the GeoServer, changing the nillable attributes to false, and then create a new WFS reader in FME, the extra xsi_nil fields are no longer present.

And after some research on the GML spec, I find that xsi_nil is an XML attribute used to indicate a nil value for an element instance, e.g.,:

<topp:SUB_REGION xsi_nil="true"></topp:SUB_REGION>

Is that the purpose for these extra fields in FME?  To accommodate the xsi_nil attribute setting?

Thanks

Sorry, I see where I should have added the above as a comment to my original post ... my bad.

Thought I'd give this post a kick. Can anyone at Safe Software give some insight on this?

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