Using Structural Joins and Holistic Twig Joins for Native XML Query Optimization

One of the most important factors for success of native XML database systems is a powerful query optimizer. Surprisingly, little has been clone to develop cost models to enable cost-based optimization in such systems. Since the entire optimization process is so complex, only a stepwise approach will lead to a satisfying (future) solution. In this work, we are paving the way for cost-based XML query optimization by developing cost formulae for two important join operators, which allow to perform join reordering and join fusion in a cost-aware way, and, therefore, make joint application of Structural Joins and Holistic Twig Joins possible.