XML parsing with SQL/PL-SQL

Question

Hi,
My question is about how can an XML message can be best parsed using SQL/PL-SQL.
The scenario is as follow. The XML message is stored in a CLOB; only some of its data needs to be extracted; there are six different types of structures of XML; the size of each XML is about 50 lines (maximum depth level is 3); the data could be written in English or Greek or French or German or Russian; this is going to be done every hour and the parsing is going to be against 3,000 records approx.
In the development, I need to take into consideration performance. We are using Oracle 10, but we could migrate to Oracle 11 if necessary.
Apologies for this basic question but I have never done XML parsing in SQL/PL-SQL before.
Thank you.
PS I have copied this question to the XML forum.
Edited by: user3112983 on May 19, 2010 3:30 PM
Edited by: user3112983 on May 19, 2010 3:39 PM

Answer 1

user3112983 wrote:
The scenario is as follow. The XML message is stored in a CLOB; only some of its data needs to be extracted; there are six different types of structures of XML; the size of each XML is about 50 lines (maximum depth level is 3); the data could be written in English or Greek or French or German or Russian; this is going to be done every hour and the parsing is going to be against 3,000 records approx.Parsing is done using the XMLTYPE data type (object class) in Oracle.
Something as follows:
SQL> create table xml_doc( id number, doc clob );
Table created.
SQL>
SQL> insert into xml_doc values( 1, '<root><row><name>John</name></row><row><name>Jack</name></row></root>' );
1 row created.
SQL> commit;
Commit complete.
SQL>
SQL> declare
  2          rawXml  xml_doc.doc%type;
  3          xml     xmltype;
  4  begin
  5          -- get the raw XML (as a CLOB)
  6          select doc into rawXml from xml_doc where id = 1;
  7
  8          -- parse it
  9          xml := new xmltype( rawXml );  
10         -- process the XML...
11  end;
12  /
PL/SQL procedure successfully completed.
SQL>The variable xml in the sample code is the XML DOM object. XML functions can be used against it (e.g. to extract values in a tabular row and column structure).
Note that the CLOB needs to contain a valid XML. An XML containing XML fragments is not valid and cannot be parsed. E.g.
SQL> declare
  2          xml     xmltype;
  3  begin
  4          -- attemp to parse fragments
  5          xml := new xmltype( '<row><name>John</name></row>  <data><column>Name</column></data>' );
  6  end;
  7  /
declare
ERROR at line 1:
ORA-31011: XML parsing failed
ORA-19202: Error occurred in XML processing
LPX-00245: extra data after end of document
Error at line 1
ORA-06512: at "SYS.XMLTYPE", line 301
ORA-06512: at line 5This XML contains 2 fragments. A row structure and a data structure. It is not a valid XML and as such cannot be parsed. If a root tag is used to encapsulate these 2 fragments, then it will be a valid XML structure.
In the development, I need to take into consideration performance. We are using Oracle 10, but we could migrate to Oracle 11 if necessary.Have not run into any XML performance problems specifically - and am using it extensively. Even large XMLs (10's of 1000's of elements) parse pretty fast.