Method and computer program for evaluating database queries involving relational and hierarchical data

摘要

A method and apparatus for resolving conjunctive queries, comprising relational predicates and external predicates, such as XML predicates. The method and apparatus obtain results from a relational engine or from an external engine, and then use the obtained results as input for the other engine, so as to optimize the activity of the other engine. The process may repeat further times, with the results obtained by the other engine being input to the first engine. The method and apparatus further disclose handling value, being isomorphic hierarchical subtrees.

主权项

1. A method for evaluating a conjunctive query, the method executed as a computer program by a general purpose computer, the conjunctive query comprising an at least one first predicate having variables; wherein the at least one first predicate is a relational predicate that is evaluated with a first engine using a relational database, and an at least one second predicate having variables, wherein the at least one second predicate is an external predicate that is evaluated using a second engine without using a relational database; the method comprising the steps of:
defining the relational predicates as untreated and defining the external predicates as untreated; receiving a first algorithm (A) that defines a method of dividing up the external predicates; extracting external predicates based on the received first algorithm (A) and marking them as treated; associating the extracted external predicates with untreated relational predicates that appear as variables of the external predicates and indicating the associated relational predicates as treated; evaluating the extracted external predicates using a second algorithm to produce a result; repeating said extracting, associating and evaluating for additional sets from the external predicates and performing a join operation on the results.