Querying markup language data sources using a relational query processor

• US 20030212664A1
• Filed: 05/10/2002
• Published: 11/13/2003
• Est. Priority Date: 05/10/2002
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Josifovski, Vanja, Schwarz, Peter M., Breining, Martin
• Granted Patent: US 7,457,810 B2
• Time in Patent Office: Days
• US Class Current: 707/3
• CPC Class Codes: G06F 16/83 Querying
• CPC Class Codes: G06F 16/84 Mapping; Conversion
• CPC Class Codes: Y10S 707/99942 Manipulating data structure, e.g. compression, compaction, compilation
• CPC Class Codes: Y10S 707/99943 Generating database or data structure, e.g. via user interface
• CPC Class Codes: Y10S 707/99944 Object-oriented database structure
• CPC Class Codes: Y10S 707/99945 Object-oriented database structure processing

Abstract

An XML wrapper queries an XML document in an on-the-fly manner so that only parent nodes in the document that satisfy the query are extracted and then unnested. The parent nodes and associated descendent nodes are located using XPath expressions contained as options in data definition language (DDL) statements. The parent nodes satisfying the query and associated descendent nodes are extracted and stored outside of a database according to a relational schema. The wrapper facilitates applications that use convention SQL queries and views to operate on that information stored according to the relational schema. The wrapper also responds to query optimizer requests for costs associated with queries against external data sources associated with the wrapper.

Claims

1. A method of querying data in a mark-up language document stored in a data source, the mark-up language document containing a plurality of nodes, the method comprising:

receiving, in response to a request to extract a node from the document, a data stream including a parent node;

evaluating the parent node with respect to a query; and

requesting, in response to evaluating the query, one or more nodes in a nested relationship with the parent node if the parent node satisfies the query.

2. The method of claim 1, further comprising mapping the data stream according to a relational schema into a plurality of tables buffered in a non-persistent memory.

3. The method of claim 2, wherein said mapping places the parent node in a first table and said one or more of the nested nodes in a second table.

4. The method of claim 2, further comprising processing the data in the plurality of tables using a database application.

5. The method of claim 1, further comprising translating the query into the request to extract the node from the document and sending the request to the data source.

6. The method of claim 5, wherein said translating the query into the request includes consulting a mapping specification to determine a location of the parent node within the document.

7. The method of claim 6, wherein said consulting a mapping specification includes evaluating an expression for locating the parent node.

8. The method of claim 7, wherein the document is an Extensible Markup Language (XML) document and the expression is an XPath expression.

9. The method of claim 8, wherein the mapping specification contains a data definition language statement with an option specifying the XPath expression.

10. The method of claim 9, wherein the query is a Structured Query Language (SQL) query.

11. A computer-readable medium of instructions for execution by a computer and suitable for specifying a mapping of a plurality of nodes contained in a mark-up language document according to a relational schema into a plurality of tables, comprising:

first program instructions for creating a first table based on a first type of node from the document, the first instructions including an option specifying a location within the mark-up language document of the first type of node; and

second program instructions for creating a second table based on a second type of node from the document, the second type of node related to the first type of node, and the second program instructions including an option specifying a location within the mark-up language document of the second type of node.

12. The computer-readable medium of instructions of claim 11, wherein the mark-up language document is an Extensible Markup Language (XML) document.

13. The computer-readable medium of instructions of claim 12, wherein the options included in the first and second instructions are XPath expressions.

14. The computer-readable medium of instructions of claim 11, wherein the second type of node is node is a child of the first type of node.

15. A method of querying a document containing hierarchical information that includes parent nodes and descendent nodes, comprising:

locating a first parent node in the document by using a mapping specification;

determining if the first parent node satisfies a query; and

fetching from the document nested descendent nodes relating to the first parent node in response to determining that the first parent node satisfies the query.

16. The method of claim 15, further comprising storing the first parent node in a first relational storage area and storing the fetched descendent nodes in a second relational storage area.

17. The method of claim 16, further comprising:

upon fetching a last nested descendent node relating to the first parent node, locating a second parent node in the document by using the mapping specification;

storing the second parent node in the first relational storage area;

fetching from the document nested descendent nodes relating to the second parent node; and

storing the fetched descendent nodes in the second relational storage area, wherein the nested descendent nodes are located by using the mapping specification.

18. The method of claim 15, wherein the nested descendent nodes are located by using the mapping specification.

19. The method of claim 15, wherein the mapping specification identifies for the first parent node, columns containing the descendent nodes relating to the first parent node.

20. The method of claim 15, wherein the document is an Extensible Markup Language (XML) document, and the mapping specification includes expressions suitable for locating the first parent node and the descendent nodes within the XML document.

21. The method of claim 20, wherein said expressions suitable for locating the first parent node and the descendent nodes within the XML document are XPath expressions.

22. A method of locating a path from a descendent node to a root node in a document containing hierarchical information, the method comprising joining a table holding information of the descendent node and a table holding information of the root node, wherein each of the tables has a primary key and a foreign key, columns of the table holding the descendent node information are selected, and predicates for the join are taken over the primary and foreign keys of the selected tables.

23. The method of claim 22, wherein the path from the descendent node to the root node contains at least one intermediate node, and said joining the tables includes joining tables holding information of said at least one intermediate node.

24. The method of claim 23, further comprising optimizing the joining of tables by rewriting a query.

25. The method of claim 22, wherein the document is a mark-up language document.

26. The method of claim 25, wherein the document is an Extensible Markup Language (XML) document.

27. A computer based system for querying a markup language document having hierarchical information including a parent node and descendent nodes related to the parent node, comprising:

a data source having stored therein a markup language document;

a wrapper unit configured to extract information from the markup language document in response to a query by consulting a mapping specification containing information for locating the parent node, and if the parent node satisfies the query to store the parent node in a first table, and to locate the descendent nodes by consulting the mapping specification if the parent node satisfies the query and store said descendent nodes in a second table.

28. The computer based system of claim 27, wherein said consulting a mapping specification includes evaluating an expression for locating the parent node.

29. The computer based system of claim 28, wherein the document is an Extensible Markup Language (XML) document and the expression is an XPath expression.

30. The computer based system of claim 29, wherein the mapping specification contains a data definition language statement with an option specifying the XPath expression.

31. The computer based system of claim 30, wherein the query is a Structured Query Language (SQL) query.

32. A computer based system for querying a markup language document having hierarchical information including a parent node and descendent nodes related to the parent node, comprising:

data source means for storing a markup language document; and

a wrapper configured to extract information from the markup language document in response to a query by consulting a mapping specification containing information for locating the parent node, the wrapper comprising;

means for storing the parent node in a first table if the parent node satisfies the query;

means for locating the descendent nodes by consulting a mapping specification; and

means for extracting the located descendent nodes if the parent node satisfies the query.

33. The computer based system of claim 32, wherein said consulting a mapping specification includes evaluating an expression for locating a node.

34. The computer based system of claim 33, wherein the document is an Extensible Markup Language (XML) document and the expression is an XPath expression.

35. The computer based system of claim 34, wherein the mapping specification contains a data definition language statement with an option specifying the XPath expression.

36. The computer based system of claim 35, wherein the query is a Structured Query Language (SQL) query.

37. A method of optimizing a query, comprising:

receiving a request for information concerning a cost of a query against a data source containing a markup language document;

determining a cost of performing the query in response to the request; and

responding to the request by providing information concerning the cost.

38. The method of claim 37, wherein the markup language document is an Extensible Markup Language (XML) document.

39. The method of claim 37, wherein the query is a Structured Query Language (SQL) query.

40. The method of claim 37, wherein the source is external to a database handling the request.

41. The method of claim 40, wherein the request is received by a wrapper suitable for managing the data source containing the XML document and the wrapper responds to a query optimizer.