A Fully Pipelined XQuery Processor

We present a high-performance, pull-based streaming processor for XQuery, called XQPull, that can handle many essential features of the language, including general predicates, recursive queries, backward axis steps, and function calls, using a very small amount of caching. Our framework is based on a new type of event streams, called retarded streams, which allow multiple and nested streams to be interleaved in the same physical stream, while postponing the caching of input events until is absolutely necessary, typically at the end of the query evaluation, just before the results are ready to print.