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Pushdown Compression Albert, Pilar Mayordomo, Elvira Moser, Philip Perifel, Sylvain Finite-state compression Lempel-Ziv algorithm pumping-lemma pushdown compression XML document The pressing need for efficient compression schemes for XML documents has recently been focused on stack computation (Hariharan and Shankar 2006, League and Eng 2007), and in particular calls for a formulation of information-lossless stack or pushdown compressors that allows a formal analysis of their performance and a more ambitious use of the stack in XML compression, where so far it is mainly connected to parsing mechanisms. In this paper we introduce the model of pushdown compressor, based on pushdown transducers that compute a single injective function while keeping the widest generality regarding stack computation. The celebrated Lempel-Ziv algorithm LZ78 was introduced as a general purpose compression algorithm that outperforms finite-state compressors on all sequences. We compare the performance of the Lempel-Ziv algorithm with that of the pushdown compressors, or compression algorithms that can be implemented with a pushdown transducer. This comparison is made without any a priori assumption on the data's source and considering the asymptotic compression ratio for infinite sequences. We prove that Lempel-Ziv is incomparable with pushdown compressors. Schloss Dagstuhl – Leibniz-Zentrum für Informatik Pilar Albert and Elvira Mayordomo and Philip Moser and Sylvain Perifel 2008 Is Part Of LIPIcs, Volume 1, 25th International Symposium on Theoretical Aspects of Computer Science (2008) InProceedings Text doc-type:ResearchArticle publishedVersion application/pdf doi:10.4230/LIPIcs.STACS.2008.1332 urn:nbn:de:0030-drops-13327 https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2008.1332 eng https://creativecommons.org/licenses/by-nd/3.0/legalcode