Rewriting node reference-based XQuery using SQL/SML

• US 7,870,124 B2
• Filed: 12/13/2007
• Issued: 01/11/2011
• Est. Priority Date: 12/13/2007
• Status: Active Grant

• Current Assignee: Oracle International Corporation (Oracle Corporation)
• Original Assignee: Oracle International Corporation (Oracle Corporation)
• Inventors: Chang, Hui Joe, Warner, James W., Liu, Zhen Hua
• Primary Examiner(s): Vo; Tim T.
• Assistant Examiner(s): OWYANG, MICHELLE N
• Application Number:
  US11/955,944
• Publication Number:
  US 20090157722A1
• Time in Patent Office: 1,125 Days
• Field of Search: 707705-780
• US Class Current: 707/718
• CPC Class Codes: G06F 16/8358 Query translation

Abstract

Techniques for processing reference-based SQL/XML operators are provided. Instead of extracting copies of one or more nodes from XML data, a reference-based operator returns a reference to a node. Such a reference is used to determine, for example, whether the corresponding node comes logical before, after, or is the same as another node. An SQL/XML query that includes a reference-based operator may be the original query, or may be generated (e.g., rewritten) from a non-SQL/XML query, such as an XQuery query. One or more physical rewrites may be performed on the SQL/XML query, depending on how the XML data is stored and/or whether an XML index exists for the XML data.

Claims

1. A method comprising:

receiving a first query that conforms to a first XML query language;

determining that an operator included in the first query requires one or more node references, to one or more nodes, as operands of the operator instead of a value of any of the one or more nodes;

wherein the operator included in the first query is one of a node comparison operator or an operator that requires context node traversal; and

in response to determining that the operator included in the first query requires one or more node references as operands of the operator, generating, based on the first query, a second query (a) that conforms to a second XML query language that is different than the first XML query language and (b) that includes a particular operator not included in the first query;

wherein execution of the particular operator included in the second query causes a reference, to a node in an XML document, to be returned instead of a value of the node;

wherein the steps are performed by one or more computing devices.

2. The method of claim 1, wherein the first XML query language is an XQuery query language.

3. The method of claim 1, wherein the second XML query language is an SQL/XML query language.

4. The method of claim 1, further comprising:

determining how XML data, that is targeted by the first query, can be accessed;

generating, based on the second query and how the XML data can be accessed, a third query that indicates one or more data structures; and

executing the third query, wherein the one or more data structures are accessed to execute the third query.

5. The method of claim 4, wherein:

determining how the XML data can be accessed includes determining that an XML index exists on the XML data; and

the one or more data structures are one or more data structures of the XML index.

6. The method of claim 4, wherein:

determining how the XML data can be accessed includes determining that the XML data is stored object-relationally; and

the one or more data structures are one or more object-relational data structures.

7. The method of claim 1, wherein the particular operator takes a path expression as input.

8. A method comprising:

executing an SQL/XML query that includes a reference-based operator, wherein the reference-based operator includes a set of one or more operands that each refer to one or more nodes of an XML document, wherein the reference-based operator is one of a node comparison operator or an operator that requires context node traversal;

wherein execution of the reference-based operator returns a reference to the one or more nodes instead of a value of the one or more nodes;

wherein executing the SQL/XML query includes;

determining a reference for each of the one or more nodes; and

generating results of the SQL/XML query based on the-reference;

wherein the steps are performed by one or more computing devices.

9. The method of claim 8, wherein the SQL/XML query is generated from compiling an XQuery query that is received by a database server.

10. The method of claim 8, wherein before executing the SQL/XML query, the method further comprises:

determining how XML data, that is targeted by the SQL/XML query, can be accessed;

generating, based on the SQL/XML query and how the XML data can be accessed, a rewritten query that indicates one or more data structures; and

executing the rewritten query, wherein the one or more data structures are accessed to execute the rewritten query.

11. The method of claim 10, wherein:

determining how the XML data can be accessed includes determining that an XML index exists on the XML data; and

the one or more data structures are one or more data structures of the XML index.

12. The method of claim 10, wherein:

determining how the XML data can be accessed includes determining that the XML data is stored object-relationally; and

the one or more data structures are one or more object-relational data structures.

13. A machine-readable storage medium storing instructions which, when executed by one or more processors, causes:

receiving a first query that conforms to a first XML query language;

determining that an operator included in the first query requires one or more node references, to one or more nodes, as operands of the operator instead of a value of any of the one or more nodes;

wherein the operator included in the first query is one of a node comparison operator or an operator that requires context node traversal; and

in response to determining that the operator included in the first query requires one or more node references as operands of the operator, generating, based on the first query, a second query (a) that conforms to a second XML query language that is different than the first XML query language and (b) that includes a particular operator not included in the first query;

wherein execution of the particular operator included in the second query causes a reference, to a node in an XML document, to be returned instead of a value of the node.

14. The machine-readable storage medium of claim 13, wherein the first XML query language is an XQuery query language.

15. The machine-readable storage medium of claim 13, wherein the second XML query language is an SQL/XML query language.

16. The machine-readable storage medium of claim 13, wherein the instructions, when executed by the one or more processors, further cause the one or more processors to perform the steps of:

determining how XML data, that is targeted by the first query, can be accessed;

generating, based on the second query and how the XML data can be accessed, a third query that indicates one or more data structures; and

executing the third query, wherein the one or more data structures are accessed to execute the third query.

17. The machine-readable storage medium of claim 16, wherein:

determining how the XML data can be accessed includes determining that an XML index exists on the XML data; and

the one or more data structures are one or more data structures of the XML index.

18. The machine-readable storage medium of claim 16, wherein:

determining how the XML data can be accessed includes determining that the XML data is stored object-relationally; and

the one or more data structures are one or more object-relational data structures.

19. The machine-readable storage medium of claim 13, wherein the particular operator takes a path expression as input.

20. A machine-readable storage medium storing instructions which, when executed by one or more processors, cause:

executing an SQL/XML query that includes a reference-based operator, wherein the reference-based operator includes a set of one or more operands that each refer to one or more nodes of an XML document, wherein the reference-based operator is one of a node comparison operator or an operator that requires context node traversal;

wherein execution of the reference-based operator returns a reference to the one or more nodes instead of a value of the one or more nodes;

wherein executing the SQL/XML query includes;

determining a reference for each of the one or more nodes; and

generating results of the SQL/XML query based on the reference.

21. The machine-readable storage medium of claim 20, wherein the SQL/XML query is generated from compiling an XQuery query that is received by a database server.

22. The machine-readable storage medium of claim 20, wherein the instructions, when executed by the one or more processors, further cause the one or more processors to perform the step of, before executing the SQL/XML query:

determining how XML data, that is targeted by the SQL/XML query, can be accessed;

generating, based on the SQL/XML query and how the XML data can be accessed, a rewritten query that indicates one or more data structures; and

executing the rewritten query, wherein the one or more data structures are accessed to execute the rewritten query.

23. The machine-readable storage medium of claim 22, wherein:

determining how the XML data can be accessed includes determining that an XML index exists on the XML data; and

the one or more data structures are one or more data structures of the XML index.

24. The machine-readable storage medium of claim 22, wherein:

determining how the XML data can be accessed includes determining that the XML data is stored object-relationally; and

the one or more data structures are one or more object-relational data structures.