The following are covered here: XQuery, XMLType operations, and indexing of XML data.

• XQuery and Oracle XML DB
  The XQuery language is one of the main ways that you interact with XML data in Oracle XML DB. Support for the language includes SQL*Plus commandXQUERY and SQL/XML functions XMLQuery, XMLTable, XMLExists, and XMLCast.
• Query and Update of XML Data
  There are many ways for applications to query and update XML data that is in Oracle Database, both XML schema-based and non-schema-based.
• Indexes for XMLType Data
  You can create indexes on your XML data, to focus on particular parts of it that you query often and thus improve performance. There are various ways that you can index XMLType data, whether it is XML schema-based or non-schema-based, and regardless of the XMLType storage model you use.
• Transformation and Validation of XMLType Data
  There are several Oracle SQL functions and XMLType APIs for transforming XMLType data using XSLT stylesheets and for validating XMLType instances against an XML schema.