Streaming XPath Processing with Forward and Backward Axes

We present a novel streaming algorithm for evaluating XPath expressions that use backward axes (parent and ancestor) and forward axes in a single document-order traversal of an XML document. Other streaming XPath processors, such as YFilter, XTrie, and TurboXPath handle only forward axes. We show through experiments that our algorithm significantly outperforms (by more than a factor of two) a traditional non-streaming XPath engine. Furthermore, since our algorithm only retains relevant portions of the input document in memory, it scales better than traditional XPath engines. It can process large documents; we have successfully tested documents over 1GB in size. On the other hand, the traditional XPath engine degrades considerably in performance for documents over 100 MB in size and fails to complete for documents of size over 200 MB.