Error when deleting and registering an xml schema

Question

Why do I get an error saying that my schema 'xsd/Envelope.xsd' already exists when I try to register it and yet I cannot delete it and it does not exist in the USER_XML_SCHEMAS table?
SQL> declare
2 begin
3 dbms_xmlschema.deleteSchema('xsd/Envelope.xsd', dbms_xmlschema.DELETE_CASCADE_FORCE);
4 end;
5 /
declare
ERROR at line 1:
ORA-31000: Resource 'xsd/Envelope.xsd' is not an XDB schema document
ORA-06512: at "XDB.DBMS_XMLSCHEMA_INT", line 0
ORA-06512: at "XDB.DBMS_XMLSCHEMA", line 100
ORA-06512: at line 3
SQL> declare
2 begin
3 DBMS_XMLSCHEMA.registerSchema('xsd/Envelope.xsd', xdbURIType('/sys/schemas/REITDIST/xsd/Envelope.xsd').getClob(), TRUE, TRUE, FALSE, FALSE);
4 end;
5 /
declare
ERROR at line 1:
ORA-31085: schema "xsd/Envelope.xsd" already registered
ORA-06512: at "XDB.DBMS_XMLSCHEMA_INT", line 0
ORA-06512: at "XDB.DBMS_XMLSCHEMA", line 26
ORA-06512: at line 3
SQL> select SCHEMA_URL, local, qual_schema_url
2 from user_xml_schemas;
no rows selected

Answer 1

dbms_xmlSchema.registerSchema
     SCHEMAURL     => <your xsd name>,
     SCHEMADOC     => <your xsd>,
     LOCAL          => TRUE,
     GENTYPES     => TRUE,
     GENTABLES     => FALSE,
     FORCE          => TRUE,
If parameter called "force" is set to TRUE, the schema registration will not raise errors. Instead, it creates an invalid XML schema object in case of any errors. By default, the value of this parameter is FALSE (http://download-uk.oracle.com/docs/cd/B28359_01/appdev.111/b28419/d_xmlsch.htm#i1003177)