Transforming XML streams with references

Abstract

Many useful xml transformations can be formulated through deterministic top-down tree transducers. If transducers process parts of the input repeatedly or in non-document order, then they cannot be realized over the xml stream with constant or even depth-bounded memory. We show that by enriching streams by forward references both in the input and in the output, every such transformation can be compiled into a stream processor with a space consumption depending only on the transducer and the depth of the xml document. References allow to produce DAG-compressed output that is guaranteed to be linear in the size of the input (up to the space required for labels). Our model is designed so that without decompression, the output may again serve as the input of a subsequent transducer.