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Compositions of n tree transducers

Published: 01 May 1972 Publication History

Abstract

Top-down tree transductions, introduced as models of syntax-directed translations and transformational grammars in [12] and [11], are not closed under relational composition. However, closure under relational composition is not always needed; for example, in establishing closure properties of surface sets.(Surface sets are tree-languages obtained as ranges of transductions.) One such closure property, whether the image of a surface set under a transduction is a surface set, remained open.
In this paper, we show that transductions need not preserve surface sets. In fact, we exhibit a hierarchy of tree languages obtained by successive transductions. We do not have a good proof that the hierarchy inclusions are proper, but there are strong reasons for so suspecting.
As is customary in tree automata papers, we spend some effort on notation. This time, we present a list of first-order axioms for plane (ordered) trees. The Gorn-Brainerd-Doner representation of trees as prefix-closed sets of sequences ([5],[2],[3]) really is a representation in the sense that any (well-founded) abstract tree satisfying our axioms is isomorphic to a prefix-closed set. We then adopt Rosen's notation [10] for trees in subsequent definitions. In our opinion, however, a universally acceptable notation remains to be discovered.

References

[1]
Berge, C. The theory of graphs. Methuen: London, 1962.
[2]
Brainerd, W.S. Tree generating regular systems. Information and Control 14 (1969), 217-;231.
[3]
Doner, J. Tree accepters and some of their applications. J. Comput. and Syst. Sci., vol. 4, no. 5 (1970), 406-;450.
[4]
Engelfriet, J. Bottomup and topdown tree transducers - a comparison. Tech. report. Technische Hogeschule Twente, Netherlands, 1971.
[5]
Gorn, S. An axiomatic approach to prefix languages. In Symbolic Languages in Data Processing, Gordon and Breach, New York (1962), 1-;21.
[6]
Jech, T.J. Trees. J. Symbolic Logic, vol. 36, no. 1 (1971), 1-;14.
[7]
Knuth, D. The Art of Computer Programming, vol. 1. Addison-Wesley, Reading, 1968.
[8]
Meyers, W. Linear representation of tree structure. Proc. Third Annual Symp. on Theory of Computing, Shaker Heights, Ohio (1971), 50-;63.
[9]
Morley, M. Partitions and models. In Proceedings of the Summer School in Logic: Leeds, 1967, Springer-Verlag Lecture notes in Mathematics, Berlin, 1968.
[10]
Rosen, B. Subtree replacement systems. Ph.D. dissertation, Harvard Univ., 1971. (To appear in J. Assoc. Comput. Mach).
[11]
Rounds, W. Mappings and grammars on trees. Math. Systems Theory, vol. 4, no. 3 (1970), 257-;287.
[12]
Thatcher, J.W. Generalized2 sequential machine maps. J. Comp. and Sys. Sci. 4, (1970), 339-;367.

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cover image ACM Conferences
STOC '72: Proceedings of the fourth annual ACM symposium on Theory of computing
May 1972
275 pages
ISBN:9781450374576
DOI:10.1145/800152
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Published: 01 May 1972

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