A pushdown machine for recursive XML processing

XML transformations are most naturally defined as recursive functions on trees. A naive implementation, however, would load the entire input XML tree into memory before processing. In contrast, programs in stream processing style minimise memory usage since it may release the memory occupied by the processed prefix of the input, but they are harder to write because the programmer is left with the burden to maintain a state. In this paper, we propose a model for XML stream processing and show that all programs written in a particular style of recursive functions on XML trees, the macro forest transducer, can be automatically translated to our stream processors. The stream processor is declarative in style, but can be implemented efficiently by a pushdown machine. We thus get the best of both worlds - program clarity, and efficiency in execution.