Multiple Path Join for Nested Relational Databases

This paper presents a solution to the problem of how to eeciently process queries which include join operations in the nested relational model. We focus on the join operation, and introduce a new join operator called P-join. The P-join operator merges two scheme trees. It combines the advantages of the extended natural join and recursive join for eecient data access. The algebraic expression of queries, when expressed using P-join, is more succinct and more easily optimized than it is when using other join operators. We also present a series of algebraic equivalences which are useful for query optimization in the nested relational model and prove the correctness of the P-join operation by adapting the criteria of faithfulness and precision of generalization.