Data processing: database and file management or data structures – Database design – Data structure types
Reexamination Certificate
1998-07-23
2001-04-17
Black, Thomas (Department: 2771)
Data processing: database and file management or data structures
Database design
Data structure types
C707S793000, C707S793000, C707S793000, C707S793000, C707S793000, C707S793000, C707S793000
Reexamination Certificate
active
06219663
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the data processing field, and more particularly, relates to a method and computer program product for implementing pushdown queries in a distributed object management system.
DESCRIPTION OF THE RELATED ART
Pushdown queries in a distributed object management system are necessary for efficiently extracting data from an underlying persistent datastore. Pushdown queries rely on the datastore query facilities such as those found in a relational database. With the distribution of objects among several address spaces it becomes difficult to ensure efficient and correct pushdown query capability.
Objects that are distributed in the network may have changed state that affects the results of the pushdown query operation.
A need exists for a mechanism that allows a query to be pushed down to the datastore query facilities that detects and corrects for object state changes affecting the results of the query.
SUMMARY OF THE INVENTION
A principal object of the present invention is to provide a method and computer program product for implementing pushdown queries in a distributed object management system. Other important objects of the present invention are to provide such method and computer program product for implementing pushdown queries substantially without negative effect and that overcome some of the disadvantages of prior art arrangements.
In brief, a method and computer program product are provided for implementing pushdown queries in a distributed object management system. A pushdown query to a system datastore is performed for a query type returning a single object. Responsive to the system datastore finding the match, checking whether the match refers to an object changed in the current transaction is performed. Responsive to the match not referring to a changed object, the object is returned. Responsive to the match referring to the changed object and the changed object matching the pushdown query, the changed object is returned. Responsive to the system datastore not finding the match, a list of changed objects in a current transaction is obtained. Each of the changed objects are in a current transactional state. An object query is performed on the changed objects in the list of changed objects.
In accordance with features of the invention, a multiple object pushdown query to the system datastore is performed for a query type returning multiple objects. Then the list of changed objects in the current transaction is obtained and the object query is performed on the changed objects. Results of the multiple object pushdown query and object query are merged and returned.
REFERENCES:
patent: 5588150 (1996-12-01), Lin et al.
patent: 5613106 (1997-03-01), Thurman et al.
patent: 5892949 (1999-04-01), Noble
patent: 5930793 (1999-07-01), Kleewein et al.
patent: 5966706 (1999-10-01), Biliris et al.
patent: 6092062 (2000-07-01), Lohman et al.
IEEE publication, “A Rule Engine for Query Transformation in Starburst and IBM DB2 C/S DBMS” by Hamid Pirahesh et al., IBM Almaden Research Center, pp. 391-400, Apr. 1997.
Baxter Randy Dee
McKeehan Michael Dennis
Pasch Mark Alan
Voldal Erik Edward
Black Thomas
International Business Machines - Corporation
Mizrahi Diane
Pennington Joan
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