Techniques for rewriting XML queries directed to relational database constructs

A computer-implemented method for executing database commands that involve generating an extensible markup language (XML) type from relational database constructs, comprising the steps of:

• determining a primitive set of XML generation operations for generating any XML construct from a relational database construct;
• determining whether a database command involves a particular XML generation operation that is not a member of the primitive set;
• and
• if it is determined that the database command involves the particular XML generation operation that is not a member of the primitive set, then
• determining a particular set of one or more XML generation operations from the primitive set that produces a same result as the particular XML generation operation, and
• using the particular set of one or more XML generation operations from the primitive set to evaluate the database command.

A computer-readable storage medium carrying one or more sequences of instructions for executing database commands that involve operations on extensible markup language (XML) constructs, wherein execution of the one or more sequences of instructions by one or more processors causes the one or more processors to perform the steps of:

• receiving a database command that includes an XML component operation for an XML document based on one or more relational database constructs;
• wherein the XML component operation is a function that operates on a component identified by an XPath expression;
• determining whether the XML component operation can be transformed to a relational database operation on a particular set of one or more relational database constructs of the set of one or more relational database constructs, wherein the relational database operation does not involve the XML component operation;
• and
• if it is determined that the XML component operation can be transformed to a relational database operation that does not involve the XML component operation, then
• rewriting the XML component operation to a particular relational database operation that does not involve the XML component operation, and
• evaluating the particular relational database operation on the particular set of one or more relational database constructs.

A computer-readable storage medium carrying one or more sequences of instructions for executing database commands that involve generating an extensible markup language (XML) type from relational database constructs, wherein execution of the one or more sequences of instructions by one or more processors causes the one or more processors to perform the steps of:

• determining a primitive set of XML generation operations for generating any XML construct from a relational database construct;
• determining whether a database command involves a particular XML generation operation that is not a member of the primitive set;
• and
• if it is determined that the database command involves the particular XML generation operation that is not a member of the primitive set, then
• determining a particular set of one or more XML generation operations from the primitive set that produces a same result as the particular XML generation operation, and
• using the particular set of one or more XML generation operations from the primitive set to evaluate the database command.