CreateSchemaBasedXML using multiple schemas

Question

I am trying to perform XSD validation against an XML document within PLSQL and I'm having an issue with getting it working. 
I have created an XMLTYPE object, which when I call isSchemaBased() against it returns 0 (false). Now obviously the XMLTYPE needs to be schema based in order to be validated, I found that you can make a schema based version by calling createSchemaBasedXML against the XMLTYPE. The problem I am having is that my schema is broken into two parts (combining the schema files is not an option unfortunately), which means that when I try and createSchemaBasedXML specifying the main schema it fails because it is unable to resolve a reference which is imported from the second XSD document.
-- lxml is the XMLTYPE which has been populated with the XML before this point
dbms_xmlschema.registerSchema(
  schemaURL => mainSchemaURL,
  schemaDoc => mainSchemaDoc,
  local => true,
  genTypes => true,
  genTables => false,
  force => true,
  enableHierarchy => dbms_xmlschema.ENABLE_HIERARCHY_NONE);
dbms_xmlschema.registerSchema(
  schemaURL => importedSchemaURL,
  schemaDoc => importedSchemaDoc,
  local => true,
  genTypes => true,
  genTables => false,
  force => true,
  enableHierarchy => dbms_xmlschema.ENABLE_HIERARCHY_NONE);
if lxml.isSchemaBased() = 1 then
  dbms_output.put_line('Schema based');
else
  dbms_output.put_line('Non-schema based');
end if;
dbms_ouput.put_line('About to apply schema');
lxml := lxml.createSchemaBasedXML(mainSchemaURL);
dbms_ouput.put_line('We don't get this far');
lxml := lxml.createSchemaBasedXML(importedSchemaURL); 
Is there any way of being able to import both the mainSchemaURL and the importedSchemaURL at the same time so that the imported schema references within the main schema don't cause the failure;
ORA-31079: unable to result reference to type [type containing imported type]
Any help or pointers would be greatly appreciated.

Answer 1

the code now gets to where it is trying to register the mainSchema but fails with an exception "invalid XML document" (which is untrue as the XSD is valid).
This was probably not the complete error message.
When I run your example I get :
ORA-31154: invalid XML document
ORA-19202: Error occurred in XML processing
LSX-00023: unknown namespace URI "App1/ImportedNamespace"
ORA-06512: at "XDB.DBMS_XMLSCHEMA_INT", line 3
ORA-06512: at "XDB.DBMS_XMLSCHEMA", line 14
ORA-06512: at line 4
Oracle is not able to resolve the definition of the imported type.
I know the specs don't make it mandatory but we also need to specify the schemaLocation in the import directive :
<xs:import namespace="App1/ImportedNamespace" schemaLocation="importedSchemaURL.xsd"/>
Complete test case :
-- Register the imported schema
begin
  dbms_xmlschema.registerSchema(
    schemaURL => 'importedSchemaURL.xsd',
    schemaDoc => '<?xml version="1.0" encoding="utf-8"?>
  <xs:schema id="App1_ImportedNamespace_v0_1_1"
      targetNamespace="App1/ImportedNamespace"
      xmlns="App1/ImportedNamespace"
      elementFormDefault="qualified"
      version="0.1.1"
      xmlns:xs="http://www.w3.org/2001/XMLSchema">
      <xs:simpleType name="ImportedType">
        <xs:restriction base="xs:string">
          <xs:minLength value="2" />
        </xs:restriction>
      </xs:simpleType>
  </xs:schema>',
    local => true,
    genTypes => false,
    genTables => false,
    enableHierarchy => dbms_xmlschema.ENABLE_HIERARCHY_NONE
end;
-- Register the main schema
begin
  dbms_xmlschema.registerSchema(
    schemaURL => 'mainSchemaURL.xsd',
    schemaDoc => '<?xml version="1.0" encoding="utf-8"?>
  <xs:schema id="App1_MainNamespace_v0_1_1"
      targetNamespace="App1/MainNamespace"
      xmlns="App1/MainNamespace"
      elementFormDefault="qualified"
      version="0.1.1"
      xmlns:xs="http://www.w3.org/2001/XMLSchema"
      xmlns:Imported="App1/ImportedNamespace">
      <xs:import namespace="App1/ImportedNamespace" schemaLocation="importedSchemaURL.xsd"/>
      <xs:complexType name="mainComplexType">
        <xs:sequence>
          <xs:element name="JustAString" type="xs:string" />
          <xs:element name="ImportedString" type="Imported:ImportedType" />
        </xs:sequence>
      </xs:complexType>
      <xs:element name="root" type="mainComplexType"/>
     </xs:schema>',
    local => true,
    genTypes => false,
    genTables => false,
    enableHierarchy => dbms_xmlschema.ENABLE_HIERARCHY_NONE
end;
Besides the schemaLocation attribute, I've just added a root element in the main schema, and registered both with genTypes = false (use that option if you don't intend to use object-relational storage).
Validation test :
SQL> declare
  2
  3    doc xmltype := xmltype(
  4  '<root xmlns="App1/MainNamespace"
  5         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  6         xsi:schemaLocation="App1/MainNamespace mainSchemaURL.xsd">
  7    <JustAString>ABC</JustAString>
  8    <ImportedString>X</ImportedString>
  9  </root>');
10
11  begin
12
13   doc.schemaValidate();
14
15  end;
16  /
declare
ERROR at line 1:
ORA-31154: invalid XML document
ORA-19202: Error occurred in XML processing
LSX-00221: "X" is too short (minimum length is 2)
ORA-06512: at "SYS.XMLTYPE", line 354
ORA-06512: at line 13
Seems to work