Functional-join processing

Inter-object references are one of the key concepts of object-relational an d object-oriented database systems. In this work, we investigate alternativ e techniques to implement inter-object references and make the best use of them in query processing, i.e., in evaluating functional joins. We will giv e a comprehensive overview and performance evaluation of all known techniqu es for simple (single-valued) as well as multi-valued functional joins. Fur thermore, we will describe special order-preserving functional-join techniq ues that are particularly attractive for decision support queries that requ ire ordered results. While most of the presentation of this paper is focuse d on object-relational and object-oriented database systems, some of the re sults can also be applied to plain relational databases because index neste d-loop joins along key/foreign-key relationships, as they are frequently fo und in relational databases, are just one particular way to execute a funct ional join.