Combining Streaming And Navigation For Evaluating XML Queries

• US 20090125480A1
• Filed: 11/08/2007
• Published: 05/14/2009
• Est. Priority Date: 11/08/2007
• Status: Active Grant

• Current Assignee: Oracle International Corporation (Oracle Corporation)
• Original Assignee: Oracle International Corporation (Oracle Corporation)
• Inventors: Zhang, Ning, Baby, Thomas, Chandrasekar, Sivasankaran, Agarwal, Nipun
• Granted Patent: US 8,180,791 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 16/8358 Query translation
• CPC Class Codes: G06F 16/8365 Query optimisation

Abstract

A query is rewritten to combine streaming evaluation and XML index evaluation. The query is rewritten to include a streaming operator (e.g. function) that, when executed, uses streaming evaluation. Further, the query is rewritten so that XML index evaluation of a path expression also produces location information that identifies the location of a node within an XML document. The streaming operator is able to exploit the location information to begin and end scanning rather than scanning the entire XML document.

Claims

1. A computer-implemented method comprising:

rewriting an original query into a rewritten query, said original query including;

first path-based expressions that evaluate to first one or more values, and

second path-based expressions;

wherein the rewritten query includes first rewritten expressions that cause the first one or more values to be computed using streaming evaluation;

wherein the rewritten query includes second rewritten expressions that correspond to said second path-based expressions; and

computing the first written expressions using a streaming evaluation; and

computing the second rewritten expressions using XML index evaluation.

2. The method of claim 1, wherein the second rewritten expressions evaluate to a certain output for location information within a representation of an XML document, wherein said output is an input to said first rewritten expressions.

3. The method of claim 2, wherein computing the first rewritten expressions includes using said location information to locate an element within said representation.

4. The method of claim 1, wherein the location information specifies a location within an LOB storing said representation.

5. The method of claim 1, wherein the first expressions are in a SELECT clause and the second expressions are within a WHERE clause.

6. The method of claim 1, wherein the first rewritten expressions include an expression that evaluates to a system-defined function not prescribed by a database language.

7. The method of claim 1, wherein after rewriting, a query optimizer compiling said rewritten query, said compiling including selecting a secondary index to use to compute said second rewritten expressions.

8. A computer-implemented method comprising:

a database server rewriting an original query into a rewritten query, said original query including;

first path-based expressions in a SELECT clause that evaluate to first one or more values, and

second path-based expressions in both a FROM clause and a WHERE clause;

wherein the rewritten query includes first rewritten expressions that cause the first one or more values to be computed using streaming evaluation;

wherein the rewritten query includes second rewritten expressions that correspond to said second path-based expressions;

said database server computing the first written expressions using streaming evaluation;

said database server computing the second rewritten expressions using XML index evaluation; and

wherein the second rewritten expressions evaluate to a certain output for location information within a representation of an XML document, wherein said output is an input to said first rewritten expressions.

9. The method of claim 8, wherein computing the first rewritten expressions includes using said location information to locate an element within said representation.

10. The method of claim 8, wherein after rewriting, a query optimizer compiling said rewritten query, said compiling including selecting a secondary index to use to compute said second rewritten expressions.

11. A computer-readable medium carrying one or more sequences of instructions, 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:

rewriting an original query into a rewritten query, said original query including;

first path-based expressions that evaluate to first one or more values, and

second path-based expressions;

wherein the rewritten query includes first rewritten expressions that cause the first one or more values to be computed using streaming evaluation;

wherein the rewritten query includes second rewritten expressions that correspond to said second path-based expressions; and

computing the first written expressions using a streaming evaluation; and

computing the second rewritten expressions using XML index evaluation.

12. The computer-readable medium of claim 11, wherein the second rewritten expressions evaluate to a certain output for location information within a representation of an XML document, wherein said output is an input to said first rewritten expressions.

13. The computer-readable medium of claim 12, wherein computing the first rewritten expressions includes using said location information to locate an element within said representation.

14. The computer-readable medium of claim 11, wherein the location information specifies a location within an LOB storing said representation.

15. The computer-readable medium of claim 11, wherein the first expressions are in a SELECT clause and the second expressions are within a WHERE clause.

16. The computer-readable medium of claim 11, wherein the first rewritten expressions include an expression that evaluates to a system-defined function not prescribed by a database language.

17. The computer-readable medium of claim 11, the steps further including:

after rewriting, a query optimizer compiling said rewritten query, said compiling including selecting a secondary index to use to compute said second rewritten expressions.

18. A computer-readable medium carrying one or more sequences of instructions, 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:

a database server rewriting an original query into a rewritten query, said original query including;

first path-based expressions in a SELECT clause that evaluate to first one or more values, and

second path-based expressions in both a FROM clause and a WHERE clause;

wherein the rewritten query includes first rewritten expressions that cause the first one or more values to be computed using streaming evaluation;

wherein the rewritten query includes second rewritten expressions that correspond to said second path-based expressions;

said database server computing the first written expressions using streaming evaluation;

said database server computing the second rewritten expressions using XML index evaluation; and

wherein the second rewritten expressions evaluate to a certain output for location information within a representation of an XML document, wherein said output is an input to said first rewritten expressions.

19. The computer-readable medium of claim 18, wherein computing the first rewritten expressions includes using said location information to locate an element within said representation.

20. The computer-readable medium of claim 18, the steps further including:

wherein after rewriting, a query optimizer compiling said rewritten query, said compiling including selecting a secondary index to use to compute said second rewritten expressions.