Indices and constraints on XML Tables/Columns (with Schema)

Question

Hi,
I've read a lot of documents by know, but the more I read the more I got confused. So I hope you can help me.
Frist my Oracle Server Version: Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit
I've manages to create a table with a column with the type SYS.XMLTYPE and the storage modle "Object Relational" with an XML Schema.
I can insert data and I can execute XQuery statements.
I can also create an XMLTYPE table with my Schema, althoug the tool SQL Developer keeps telling me, that the one column wich is generated within the table is of the type CLOB instead of object realtional (which is what I defined).
The query for that is:
CREATE TABLE ENTRY_XML OF XMLTYPE
XMLTYPE STORE AS OBJECT RELATIONAL
XMLSCHEMA "BBMRI_Entry.xsd" ELEMENT "Entry";
That's where I am, now my questions:
1. What's the difference? I'm aware of the obviouse difference, that with the first way I can add relational columns as well, but apart from that? If I only want to store the xml data, is the second approach always better (especially in regard to my next question)?
2. My schema contains elements with attributes (which contain IDs), which have to be unique. So I tried to add a UNIQUE constraint, but failed. I found this (http://www.oracle.com/technology/sample_code/tech/java/codesnippet/xmldb/constraints/Specify_Constraints.html), but it just doesn't work.
Query: "ALTER TABLE ENTRY_XML CONSTRAINT ENTRY_XML_SUBID_UNQIUE UNIQUE (xmldata."SubId");"
Error: "ORA-01735: invalid ALTER TABLE option"
3. I didn't try yet, but I need to specifiy foreign keys within the XML as well (which is explained in the link at question 2). I guess the solution to question 2 will make this possible as well.
4. Since I can create a UNIQUE constaint for attributes (well, I can't yet, but I hope that this will change soon) I woundered if it would be possible to realize something like auto_increment. Although I see the problem with validating the xml input if the Ids are empty. Any suggestions on that problem? Do I have to query for the highest (free) id before I can insert the new documents?
Well, that's enough for today, I hope someone can help me!
Greetings, Florian

Answer 1

I've read through all the literature (again) and found out, that I did most of the stuff right in the first place. I just missinterpreted the generated tables for the types and wondered why they only contained one column. Well, at least one mistery solved.
But know to make it easier just one question, which might solve all problems I have:
How can I create UNIQUE constraints and FOREIGN KEYS when I have a table or column of the type XmlType with a schema using the object relational storage method?
I found a solution http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14259/xdb05sto.htm#i1042421 (Example 5-12), but it just does not work for me.
I removed the FOREIGN KEY and tried it again and the UNIQUE Key works.
So basically the question is how to retrieve the "AId" Attribute. "XMLDATA"."AId", "XMLDATA"."Attribute"."AId" and "XMLDATA"."Subject"."Attribute"."AId" all do not work.
I've added my schema declarations at the bottom (which I've already successfully registred and used without foreign keys and constraints, so they work).
After I've registered the two schema files 3 types and 11 tables where created. One type for the attribute, one for the study type and one probably to link the attributes to the study types. The tables are one for the attribute, 4 for the content*-elements, 2 for the study type (I don't really know why two) and 4 with strange names starting with "SYS_NT" and then some random numbers and letters (looks alot like some base64 encoded string).
The Query I try to use to create the table is: (The table "Attribute" already exists and contains a field "ID", which is it's PK.)
CREATE TABLE STUDYTYPE_XML
OF XMLType (UNIQUE ("XMLDATA"."STId"),
FOREIGN KEY ("XMLDATA"."AId") REFERENCES ATTRIBUTE(ID))
XMLTYPE STORE AS OBJECT RELATIONAL
ELEMENT "StudyType.xsd#StudyType";
The error I get is:
Error starting at line 1 in command:
CREATE TABLE STUDYTYPE_XML
OF XMLType (UNIQUE ("XMLDATA"."STId"),
FOREIGN KEY ("XMLDATA"."AId") REFERENCES ATTRIBUTE(ID))
ELEMENT "StudyType.xsd#StudyType"
Error at Command Line:3 Column:37
Error report:
SQL Error: ORA-22809: nonexistent attribute
22809. 00000 - "nonexistent attribute"
Cause: An attempt was made to access a non-existent attribute of an
object type.
Action: Check the attribute reference to see if it is valid. Then retry
the operation.
Attribute-Schema (Attribute.xsd):
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified">
     <xs:attribute name="AId">
          <xs:simpleType>
               <xs:restriction base="xs:integer">
                    <xs:minInclusive value="0" />
               </xs:restriction>
          </xs:simpleType>
     </xs:attribute>
     <xs:attribute name="Name" type="xs:string" />
     <xs:element name="ContentString" type="xs:string" />
     <xs:element name="ContentInteger" type="xs:integer" />
     <xs:element name="ContentDouble" type="xs:decimal" />
     <xs:element name="ContentDate" type="xs:date" />
     <xs:element name="Attribute">
          <xs:complexType>
               <xs:choice minOccurs="0" maxOccurs="1">
                    <xs:element ref="ContentString" />
                    <xs:element ref="ContentInteger" />
                    <xs:element ref="ContentDouble" />
                    <xs:element ref="ContentDate" />
               </xs:choice>
               <xs:attribute ref="AId" use="required" />
               <xs:attribute ref="Name" use="optional" />
          </xs:complexType>
     </xs:element>
</xs:schema>
Study Type Schema (StudyType.xsd):
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified">
     <xs:include schemaLocation="Attribute.xsd" />
     <xs:attribute name="STId">
          <xs:simpleType>
               <xs:restriction base="xs:integer">
                    <xs:minInclusive value="0" />
               </xs:restriction>
          </xs:simpleType>
     </xs:attribute>
     <xs:element name="StudyType">
          <xs:complexType>
               <xs:sequence>
                    <xs:element ref="Attribute" minOccurs="1" maxOccurs="unbounded" />
                    <xs:element ref="StudyType" minOccurs="0" maxOccurs="unbounded" />
               </xs:sequence>
               <xs:attribute ref="STId" use="required"/>
          </xs:complexType>
     </xs:element>
</xs:schema>
Edited by: alwaysspam on Sep 8, 2010 5:35 PM