Efficient implementation of typed view hierarchies for ORDBMS

• US 6,421,658 B1
• Filed: 07/30/1999
• Issued: 07/16/2002
• Est. Priority Date: 07/30/1999
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Carey, Michael J., Pirahesh, Mir Hamid, Lapis, George, Vance, Bennet, Rielau, Serge P.
• Primary Examiner(s): Corrielus, Jean M.
• Assistant Examiner(s): TRUONG, CAM Y T
• Application Number:
  US09/365,590
• Time in Patent Office: 1,082 Days
• Field of Search: 707/3, 707/104, 707/5, 707/2, 707/10, 707/1, 207/1-3, 207/10, 207/5
• US Class Current: 1/1
• CPC Class Codes: G06F 16/284 Relational databases
• CPC Class Codes: Y10S 707/99931 Database or file accessing
• CPC Class Codes: Y10S 707/99932 Access augmentation or optimizing
• CPC Class Codes: Y10S 707/99933 Query processing, i.e. searching
• CPC Class Codes: Y10S 707/99935 Query augmenting and refining, e.g. inexact access
• CPC Class Codes: Y10S 707/99945 Object-oriented database structure processing

Abstract

A method for typed view hierarchies for an object-relational database management (OPDBMS). The views in the hierarchy are merged into a unified hierarchy view through case expressions for mapping and wrapping of overloaded columns. During the merge, the underlying logical tables are eliminated which results in a simplified query graph. The transformation is a non-loss operation which condenses the type information within the case expressions. This allows update, delete and insert operations to be resolved on the query graph on a local level. Using query rewrite rules, the case expressions may be simplified further.

Claims

1. In a relational database management system, a method for creating a hierarchy view on top of a table hierarchy, comprising:

(a) storing a user definition for a table hierarchy and a table type hierarchy, wherein the table hierarchy includes a physical table storing all columns of one or more typed tables in the table type hierarchy; and

(b) generating a hierarchy view from the table hierarchy and table type hierarchy, wherein the hierarchy view comprises a single unified view on the table hierarchy comprised of one or more logical views for each of the typed tables in the table type hierarchy.

2. The method as claimed in claim 1, wherein the hierarchy view is shareable by one or more query targets.

3. The method as claimed in claim 2, wherein said step (b) of generating a hierarchy view comprises merging the logical views specified in a view type hierarchy into a case expression for type mapping of rows read from the table hierarchy.

4. The method as claimed in claim 3, further including the step of using a case expression in a select list to unify expressions in the select list of a logical view in the view type hierarchy.

5. The method as claimed in claim 1, wherein more than one table hierarchy is stored, and further including the steps of generating a hierarchy view for each of the table hierarchies and grouping the hierarchy views according to the underlying table hierarchies.

6. The method as claimed in claim 1, wherein logical views are used as query targets for accessing the hierarchy view.

7. The method as claimed in claim 3, wherein said step of merging the logical views into a case expression comprises (i) generating an empty case for a first view in the view type hierarchy, (ii) determining if an expression exists for columns in the first view, (iii) if the expression exists, then adding a typecode for the first view to a corresponding branch in the case expression, (iv) if the expression does not exist, then adding a new branch for the columns, and (v) repeating steps (ii) to (iv) for other logical views.

18. The method as claimed in claim 2, wherein more than one table hierarchy is stored, and further including the steps of generating a hierarchy view for each of the table hierarchies and grouping the hierarchy views according to the underlying table hierarchies.

19. The method as claimed in claim 2, wherein logical views are used as query targets for accessing the hierarchy view.

8. A computer program product for use on a computer wherein queries are entered for retrieving data from tables stored in memory and wherein means are included for defining a table hierarchy for retrieving data from the tables, said computer program product comprising:

a recording medium;

means recorded on said medium for instructing said computer to perform the steps of,

(a) storing a user definition for a table hierarchy and a table type hierarchy, wherein the table hierarchy includes a physical table storing all columns of one or more typed tables in the table type hierarchy; and

(b) generating a hierarchy view from the table hierarchy and table type hierarchy, wherein the hierarchy view comprises a single unified view on the table hierarchy comprised of one or more logical views for each of the typed tables in the table type hierarchy.

9. The computer program product as claimed in claim 8, wherein the hierarchy view is shareable by one or more query targets.

10. The computer program product as claimed in claim 9, wherein said step (b) of generating a hierarchy view comprises merging the logical views specified in a view type hierarchy into a case expression for type mapping of rows read from the table hierarchy.

11. The computer program product as claimed in claim 10, further including the step of using a case expression in a select list to unify expressions in the select list of a logical view in the view type hierarchy.

12. The computer program product as claimed in claim 8, wherein more than one table hierarchy is stored, and further including the steps of generating a hierarchy view for each of the table hierarchies and grouping the hierarchy views according to the underlying table hierarchies.

13. The computer program product as claimed in claim 8, wherein logical views are used as query targets for accessing the hierarchy view.

14. The computer program product as claimed in claim 10, wherein said step of merging the logical views into a case expression comprises (i) generating an empty case for a first view in the view type hierarchy, (ii) determining if an expression exists for columns in the first view, (iii) if the expression exists, then adding a typecode for the first view to a corresponding branch in the case expression, (iv) if the expression does not exist, then adding a new branch for the columns, and (v) repeating steps (ii) to (iv) for other logical views.

15. A relational database management system for use with a computer system wherein queries are entered for retrieving data from tables and wherein means are included for defining a table hierarchy for retrieving data from the tables, said system comprising:

(a) means for receiving a user definition for a table hierarchy and a table type hierarchy, wherein the table hierarchy includes a physical table storing all columns of one or more typed tables in the table type hierarchy; and

(b) means for generating a hierarchy view from the table hierarchy and the table type hierarchy, wherein the hierarchy view comprises a single unified view on the table hierarchy comprised of one or more logical views for each of the typed tables in table type hierarchy.

16. The relational database management system as claimed in claim 15, wherein the hierarchy view is shareable by one or more query targets.

17. The relational database management system as claimed in claim 16, wherein said means for generating include means for merging the views specified in a view type hierarchy into a case expression for type mapping of rows read from the table hierarchy.