Can't delete from parent table if FK constraint on the out-of-line table

Question

Using Oracle XML DB 11g
I am using out-of-line storage table to store a collection of XML elements in conjuction with storeVarrayAsTable="true". So what I have is a parent table containing a nested table of VARRAY of REFs to rows in the out-of-line table.
In addition, I have a foreign key constraint placed on a column in the out-of-line table.
My problem is that I am not able to delete rows from the parent table when the FK constraint is placed on the out-of-line table. Only when I drop the FK constraint does the deletion work - all associated rows in the nested table and out-of-line table
gets deleted correctly.
With the FK constraint, deleting the child document like this
dbms_xdb.deleteResource('/project-1.xml')
gives me this error:
ORA-31018: Error deleting XML document
ORA-03001: unimplemented feature
*Cause:  The XMLType object pointed to by the given REF could not
be deleted because either the REF was invalid or it pointed to a non-existent table.
     *Action:  Either use FORCE deletion or supply a valid REF.
I have tried deleting with the FORCE options as well with no success.
Using DBMS_XDB.DELETE_RECURSIVE_FORCE option doesn't produce an error, but doesn't perform the deletion either.
Here is the XML Schema:
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xdb="http://xmlns.oracle.com/xdb" xmlns:xlink="http://www.w3.org/1999/xlink"
elementFormDefault="qualified" attributeFormDefault="unqualified" xdb:storeVarrayAsTable="true">
<xs:import namespace="http://www.w3.org/1999/xlink" schemaLocation="http://www.w3.org/1999/xlink.xsd"/>
<xs:element name="project" xdb:defaultTable="PROJECT_TAB">
<xs:complexType xdb:SQLType="PROJECT_TYP">
<xs:sequence>
<xs:element name="resourceList" minOccurs="0" xdb:SQLName="RESOURCE_LIST">
<xs:complexType xdb:SQLType="RESOURCE_LIST_TYP">
<xs:sequence>
<xs:element name="aResource" type="refType" minOccurs="0" maxOccurs="unbounded" xdb:SQLInline="false"
xdb:SQLName="A_RESOURCE_REF" xdb:defaultTable="RESOURCE_REF_TAB"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
<xs:attribute name="aguid" type="xs:string" use="required" xdb:SQLName="AGUID"/>
</xs:complexType>
</xs:element>
<xs:element name="aResource" xdb:defaultTable="A_RESOURCE_TAB">
<xs:complexType xdb:SQLType="A_RESOURCE_TYP">
<xs:complexContent>
<xs:extension base="contactType">
<xs:attribute name="aguid" type="xs:string" use="required" xdb:SQLName="AGUID"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
</xs:element>
<xs:complexType name="contactType" xdb:SQLType="CONTACT_TYP">
<xs:sequence>
<xs:element name="name" type="xs:string" xdb:SQLName="NAME"/>
<xs:element name="email" type="xs:string" minOccurs="0" xdb:SQLName="EMAIL"/>
<xs:element name="phone" type="xs:string" xdb:SQLName="PHONE"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="refType" xdb:SQLType="REF_TYP">
<xs:attribute ref="xlink:href" use="required"/>
<xs:attribute name="oref" type="xs:string" use="optional" xdb:SQLName="OREF"/>
</xs:complexType>
</xs:schema>
I registered the schema using structured storage with these options:
BEGIN
DBMS_XMLSCHEMA.registerschema(
SCHEMAURL => 'LSDProjects.xsd',
SCHEMADOC => xdbURIType('/home/LSDProject2/LSDProjects.xsd').getClob(),
LOCAL => TRUE, -- local
GENTYPES => TRUE, -- generate object types
GENBEAN => FALSE, -- no java beans
GENTABLES => TRUE -- generate object tables
END;
The PK and FK constraints were added like this:
-- Add PK constraints on aResource/@aguid attributes
ALTER TABLE A_RESOURCE_TAB ADD CONSTRAINT A_RESOURCE_AGUID_IS_UNIQUE UNIQUE (XMLDATA."AGUID");
-- Add FK constraint on out-of-line table
ALTER TABLE RESOURCE_REF_TAB
ADD (CONSTRAINT ref_resource_aguid_is_valid FOREIGN KEY (XMLDATA."OREF")
REFERENCES A_RESOURCE_TAB(XMLDATA."AGUID"));
Here are the XML instance documents:
     where resource-1.xml looks like this :
<aResource aguid="resource-1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="LSDProjects.xsd">
     <name>Jane Doe</name>
     <email>[email protected]</email>
<phone/>
</aResource>
     and project-1.xml looks like this :
     <project aguid="project-1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="LSDProjects.xsd"
               xmlns:xlink="http://www.w3.org/1999/xlink">               
          <resourceList>
               <aResource xlink:href="/resource-1.xml" oref="resource-1"/>                         
          </resourceList>     
     </project>
where <project> document contains a collection of <aResource> elements stored in the out-of-line table and
project/@oref attribute is a foreign key to the primary aResource/@aguid attribute.
Can someone shed some light on why I am unable to delete "project-1.xml" from the repository when the FK constraint is applied onto the out-of-line table.
Any advice/suggestions would be appreciated. Thanks!

Answer 1

Thank you for the quick reply, mdrake.
I am currently prototyping and testing out (best) ways to achieve data integrity with XML data in XML DB.
I have instance documents that makes cross references to values in other instance documents
(not of the same root nodes). What I'm trying to enforce is a referential constraint between the documents
so that a document cannot be inserted if the referenced document doesn't exists.
In this situation, a <project> document contains a collection of elements with @oref attributes.
The collection is stored in an out-of-line table.
For example:
<project>
<resourceList>
<aResource ... oref="resource-1"/>
<aResource ... oref="resource-2"/>
</resourceList>
</project>
The @oref (FK) attribute above references a @aguid (PK) attribute in <aResource> document (below):
<aResource aguid="resource-1"> .... </aResource>
Basically, I want to ensure that the value of
/project/resourceList/aResource/@oref
correspond to a valid
/aResource/@aguid
Note that I was able to add the FK constraint on the OOL table without any issues.
And the constraint did work as expected as I was not allowed to insert a <project> document
that referenced a non-existent /aResource/@aguid.
The problem was that I could not delete the <project> document from the XML DB repository
once the FK contraint was added. Deleting with the DELETE_RECURSIVE_FORCE option did not give
me any errors - is just didn't do anything.
I guess there are certain limitations with using out-of-line tables.
BTW, sorry the examples are hard to read as the indentations are removed when posting.