Referential constraints on XMLType tables

Question

Hi all,
I'm trying to create an XMLType table with a foreign key that references another XMLType table. Shouldn't be a big deal, i thought.
CREATE TABLE datasets (
ID NUMBER,
XML XMLTYPE )
XMLTYPE COLUMN XML XMLSCHEMA "dataset_schema.xsd" ELEMENT "root";
CREATE TABLE categories OF XMLTYPE XMLSCHEMA "categories.xsd" ELEMENT "categories";
ALTER TABLE datasets
2 ADD CONSTRAINT dataset_isvalid
3 FOREIGN KEY(XML.XMLDATA."dataset"."metaInformation"."referenceFunction"."category")
4 REFERENCES categories(XMLDATA."category"."name");
FOREIGN KEY(XML.XMLDATA."dataset"."metaInformation"."referenceFunction"."category")
ERROR at line 3:
ORA-22809: nonexistent attribute
I've then been reading through the postings regarding foreign key and unique constraints and i've managed to understand the concept of nested tables. To my dismay, trying to establish referential constraints my nested tables would throw an ORA-30730 stating this cannot be done.
I've simplified my schemas a little so it won't get to complicated: one table will store datasets and the other will hold category names.
The schema for the categories is
<?xml version="1.0" encoding="UTF-8"?>
<!-- schema for categories -->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
     <xs:element name="categories">
          <xs:complexType>
               <xs:sequence>
                    <xs:element name="category" type="categoryType" maxOccurs="unbounded"/>
               </xs:sequence>
          </xs:complexType>
     </xs:element>
     <xs:complexType name="categoryType">
          <xs:sequence>
               <xs:element name="subCategory" type="subCategoryType" maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="name" type="xs:string" use="required"/>
          <xs:attribute name="localName" type="xs:string" use="required"/>
          <xs:attribute name="type" type="xs:byte" use="required"/>
     </xs:complexType>
     <xs:complexType name="subCategoryType">
          <xs:attribute name="name" type="xs:string" use="required"/>
          <xs:attribute name="localName" type="xs:string" use="required"/>
     </xs:complexType>
</xs:schema>
and the schema for the dataset table is
<?xml version="1.0" encoding="UTF-8"?>
<!- dataset schema-->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
     <xs:complexType name="datasetType">
          <xs:sequence>
               <xs:element name="metaInformation" type="metaInformationType"/>
               <xs:element ref="otherInformation"/>
          </xs:sequence>
     </xs:complexType>
     <xs:complexType name="metaInformationType">
          <xs:sequence>
               <xs:element name="referenceFunction" type="referenceFunctionType"/>
          </xs:sequence>
     </xs:complexType>
     <xs:element name="otherInformation" type="xs:string"/>
     <xs:complexType name="referenceFunctionType">
          <xs:attribute name="name" type="xs:string" use="required"/>
          <xs:attribute name="category" type="xs:string" use="required"/>
          <xs:attribute name="subCategory" type="xs:string" use="required"/>
     </xs:complexType>
     <xs:element name="root">
          <xs:complexType>
               <xs:sequence>
                    <xs:element name="dataset" type="datasetType" maxOccurs="unbounded"/>
               </xs:sequence>
          </xs:complexType>
     </xs:element>
</xs:schema>
Now I want to define the referenceFunction/@category attribute of the dataset to be a foreign key to the categories table. Is it possible at all to do that with constraints? After failing with the nested table approach I really do not have any clue I would greatly appreciate any hints.
Thanks,
oli

Answer 1

Nested tables do not currently support referential integrity.
Foreign Keys on elements with maxOccurs > 0