Problems using mathml XML Schema in XMLDB

Question

I have successfully loaded the hierarchy of XML Schema definition documents for the current 'mathml' by adjusting the relative paths in all include and import statements, and by forcing the load to overcome cyclic dependency issues.
However when I try to create a table using the XMLTYPE or register another schema which is dependent on mathml I receive the following error:
ERROR at line 1:
ORA-31079: unable to resolve reference to group "Content-expr.class"
ORA-06512: at "XDB.DBMS_XMLSCHEMA_INT", line 37
ORA-06512: at "XDB.DBMS_XMLSCHEMA", line 61
ORA-06512: at "XDB.DBMS_XMLSCHEMA", line 126
ORA-06512: at line 14
Having tried loading into both 9iR2 and 10GR2 databases and pasting the document containing the 'Content-expr.class' into the parent document (i.e. removing the include) I have come to the conclusion that there is a problem with the schema definition.
However being new to XML I do not know what ths issue is as the file containing the definition (math.xsd) is included well before the references in the parent document.
Here is the group definition corresponding to the offending reference:
<xs:group name="Content-expr.class">
<xs:choice>
<xs:group ref="ContExpr.class"/>
<xs:group ref="PresExpr.class"/>
</xs:choice>
</xs:group>
I am also unable to trace which reference is causing the problem as there are several.
Does anyone have any suggestions as to what could be causing this issue, or how I can obtain further diagnostics?
Any help much appreciated.
Robert Honeyman
*********** New info ***************
OK. I have tried further to register the schema, and have the following additional information.
I determined that I thought my problem was cyclic dependencies being resolved ONLY by virtue of the parent file mathml2.xsd. I therefore pasted all the files together in include order so that this was no longer an issue. I then performed the following actions:
1. I tried to register into Oracle 9iR2 database (9.2.0.4) and received the following error:
ERROR at line 1:
ORA-31151: Cyclic definition encountered for group: "Content-expr.class"
ORA-06512: at "XDB.DBMS_XMLSCHEMA_INT", line 0
ORA-06512: at "XDB.DBMS_XMLSCHEMA", line 26
ORA-06512: at "XDB.DBMS_XMLSCHEMA", line 131
ORA-06512: at line 14
2. I then tried registering the schema into an Oracle 10G Release 2 database as well, and received the following error:
ORA-31084: error while creating table "MEDLINE"."math729_TAB" for element
"math"
ORA-01792: maximum number of columns in a table or view is 1000
ORA-02310: exceeded maximum number of allowable columns in table
ORA-06512: at "XDB.DBMS_XMLSCHEMA_INT", line 37
ORA-06512: at "XDB.DBMS_XMLSCHEMA", line 61
ORA-06512: at "XDB.DBMS_XMLSCHEMA", line 126
ORA-06512: at line 14
My conclusions are as follows:
1. 9iR2 (the version I was using at least 9.2.0.4) can't handle cyclic dependencies at all, or at least not complex ones.
2. Neither 9iR2 or 10gR2 can handle cyclic dependencies (or other dependent definitions managed purely by virtue of a parent file with multiple include statements)
3. 10gR2 can handle cyclic dependencies when they are all defined in the same file or resolved by an explicit include regardless of complexity.
4. 10gR2 cannot handle highly complex XML Schema definitions due its limit of 1000 columns per table.
Does anyone have any comments on these conclusions?
I don't even want to handle Mathml, just another schema definition that imports it. I may try to make my own adjustments.
Message was edited by:
rhoneyman
null

Answer 1

Thanks, I found the relevant sections in the XML DB 10GR2 documentation (chapter 3 I think). As far as I can tell my options are to either use one of the following:
- top-down technique creating tables for sub elements in the schema definition
- bottom-up technique collapsing some of the lower elements into CLOBs (I guess this is semi-structured storage)
The problem with Mathml is that it seems quite complex, with only one global schema element and many nested elements, hence only one table is created by XMLDB and it logically follows that we run out of columns.
To get it to work is likely to involve a fair amount of manual schema modification, which incurs a maintenance overhead for me.
It would be good if Oracle could provide a way of simplifying this maintenance of complex schemas to get them to be registered. I guess this would be increasing the number of columns alllowed for a table or offering some other parametric option for DBMS_XMLSCHEMA.REGISTER_SCHEMA that allowed a threshold and either a top-down or bottom-up approach to be taken automatically.
For the time being I am using a simplified schema that does not depend on Mathml for my storage needs.