The hybrid technique for reference materialization in object query processing

Resolving object references, or reference materialization, is a fundamental operation in object query evaluation. Existing reference materialization techniques fall into two categories: pointer-based and value-based. We identify several drawbacks of existing techniques and propose a hybrid technique that combines the advantages of each category. This technique relaxes the limitations of value-based techniques, while preserving much of their performance advantage over pointer-based techniques; it performs well in those cases where no existing algorithm is applicable or efficient. The hybrid technique shows even stronger performance advantages when moving from single-valued to collection-valued attributes. We present algebraic transformations to enable the hybrid technique in a rule-based query optimizer. Initial experimental results using a commercial object-oriented database show that the hybrid approach achieves significant speedup over current algorithms in many cases. The initial motivation for our work was the optimization and evaluation of object-oriented query languages, particularly OQL. However, the key features we have concentrated on, namely references and collection-valued attributes, are present in object-relational products and the SQL:1999 proposal