Efficient recursive XML query processing in relational database systems

There is growing evidence that schema-conscious approaches are a better option than schema-oblivious techniques as far as XML query performance is concerned in relational environment. However, the issue of recursive XML queries for such approaches has not been dealt with satisfactorily. In this paper we argue that it is possible to design a schema-oblivious approach that outperforms schema-conscious approaches for certain types of recursive queries. To that end, we propose a novel schema-oblivious approach called SUCXENT++ that outperforms existing schema-oblivious approaches such as XParent by up to 15 times and schema-conscious approaches (Shared-Inlining) by up to 3 times for recursive query execution. Our approach has up to 2 times smaller storage requirements compared to existing schema-oblivious approaches and 10% less than schema-conscious techniques. In addition, existing schema-oblivious approaches are hampered by poor query plans generated by the relational query optimizer. We propose optimizations in the XML query to SQL translation process that generate queries with more optimal query plans.