Techniques for partial rewrite of XPath queries in a relational database

• US 20050065949A1
• Filed: 11/08/2004
• Published: 03/24/2005
• Est. Priority Date: 05/01/2003
• Status: Active Grant

• Current Assignee: Oracle International Corporation (Oracle Corporation)
• Original Assignee: Oracle International Corporation (Oracle Corporation)
• Inventors: Manikutty, Anand, Arora, Vikas, Angrish, Rohan, Warner, James W., Krishnaprasad, Muralidhar, Liu, Zhen Hua, Kotsovolos, Susan M.
• Granted Patent: US 7,386,568 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 16/24534 Query rewriting; Transformation
• CPC Class Codes: G06F 16/8373 Query execution
• CPC Class Codes: G06F 16/86 Mapping to a database
• CPC Class Codes: Y10S 707/99943 Generating database or data structure, e.g. via user interface

Abstract

Techniques are described for executing queries that have XPath sections that specify unmappable paths. The techniques involve splitting the unmappable paths into (1) a mappable path fragment, and (2) an unmappable path fragment. After an unmappable path has been split into a mappable path fragment and an unmappable path fragment, the XPath section is replaced with a replacement XPath section. The replacement XPath section specifies two operations: a “mappable operation” that is based on the mappable path fragment, and an “unmappable operation” that is based on the unmappable path fragment. The portion of the replacement XPath section that specifies the mappable operation is rewritten to access underlying relational structures. Consequently, when the rewritten query is executed, a smaller amount of XML data needs to be materialized to evaluate the unmappable path fragment than would otherwise have been required to evaluate the original unmappable path.

Claims

1. A method for processing a database command that includes an XPath section with an unmappable path, the method comprising the steps of:

splitting the unmappable path into a plurality of path fragments, wherein the plurality of path fragments includes a mappable path fragment and an unmappable path fragment; and

replacing the XPath section with a replacement XPath section that specifies operations involving path fragments from the plurality of path fragments,

wherein the operations include;

a mappable operation whose target is defined by the mappable path fragment; and

an unmappable operation whose target is defined by the unmappable path fragment.

2. The method of claim 1 wherein:

the mappable operation is defined by a particular portion of the replacement XPath section; and

the method further comprises the step of rewriting the particular portion prior to executing the database command.

3. The method of claim 2 wherein the step of rewriting the particular portion includes rewriting the particular portion over structured schema-based storage.

4. The method of claim 2 wherein the step of rewriting the particular portion includes rewriting the particular portion over one or more SQL/XML views.

5. The method of claim 2 wherein the step of rewriting the particular portion includes rewriting the particular portion over one or more object views.

6. The method of claim 2 wherein the step of rewriting the particular portion includes rewriting the particular portion over a combination of two or more storage types from a set of storage types that consists of object views, SQL/XML views, and structured schema-based storage.

7. The method of claim 1 wherein the method further includes determining that the unmappable path can be split into mappable and unmappable fragments prior to splitting the unmappable path into a mappable path fragment and an unmappable path fragment.

8. The method of claim 7 wherein the step of determining that the unmappable path can be split into mappable and unmappable fragments includes determining that the unmappable path does not have an unmappable element as the first node in the unmappable path.

9. The method of claim 7 wherein the step of determining that the unmappable path can be split into mappable and unmappable fragments includes determining that the unmappable path does not point to a collection element.

10. The method of claim 7 wherein the step of determining that the unmappable path can be split into mappable and unmappable fragments includes determining that the unmappable path does not have a reference to an ancestor, ancestor-or-self, preceding, preceding-sibling, parent, following, or following-sibling axis at any level beneath an unrewritable node.

11. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 1.

12. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 2.

13. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 3.

14. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 4.

15. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 5.

16. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 6.

17. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 7.

18. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 8.

19. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 9.

20. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 10.