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GML attributes "owns"

It seems that in GML files, when an attribute is voidable in the conceptual UML schema, it creates in the physical GML schema, in addition to the nilReason, an element called "owns" that is a boolean. We don't understand what is the interest of this element and how it should be filled (we just try to fill it in order to make it accepted by the validator) but without understanding anything!

Can anyone help and provide us some explanations?




    By Pawel SOCZEWSKI

    According to ISO 19136 ( Ownership of property values) "owns" attribute is used only with referenced GML object (gml:OwnershipAttributeGroup). It means then the referenced object is “owned” by the parent feature, i.e.

    <Car gml:id=”c123”>

    <hasParts owns=”true” xlink:href=”urn:x-abc:id:x123”/>

    <!-- … -->


    the part will be deleted, if the car is deleted. 

    The default values of "owns" is "false". According Annex E "true" should be used in association role if type of association is "composition".

    I don't understand why "owns" is added at nilReason. I'm used Geoserver to generate GML and it doesn't do it :)

  • Stefania MORRONE

    By Stefania MORRONE

    Hi all,

    the "owns" attribute is not 'added' at nilReason, though it might seem so. When dealing with references, in fact,  "nilReason" comes from gml:AssociationAttributeGroup which is an attribute group e.g.for 'gml:ReferenceType', together with the gml:OwnershipAttributeGroup. Therefore, when there is a schema element  (e.g. an association or a code list) whose data type is gml:ReferenceType or another data type for which those attributeGroups are specified, both "owns" and "nilReason" attributes appear.

    That said, the "owns" attribute is optional so there is no obligation to fill.

    On a side note: this "nilReason" attribute (coming together with the "owns" attribute) does not mean that the schema element itself is voidable!

    Hope this helps,


  • Heidi VANPARYS

    By Heidi VANPARYS

    I think that the ownership concept comes from the UML specification. It does not seem to be defined very clear there either, see a discussion of the topic at

    As Stefania already mentioned, the owns and nilReason attributes are not related. 

    At my agency, we do not fill this attribute.

  • Peter PARSLOW

    The GML "OwnershipAttributeGroup" is defined in the GML spec (OGC document 07-036, currently at v3.2.1, equivalent to ISO 19136; clause The text of the documentation is copied in the relevant schema file (