. We deal with matching and locating of patterns in forests of variable arity. A pattern consists of a structural and a contextual condition for subtrees of a forest, both of which are given as tree or forest regular languages. We use the notation of constraint systems to uniformly specify both kinds of conditions. In order to implement pattern matching we introduce the class of pushdown forest automata. We identify a special class of contexts such that not only pattern matching but also locating all of a forest's subtrees matching in context can be performed in a single traversal. We also give a method for computing the reachable states of an automaton in order to minimize the size of transition tables. 1 Introduction In Standard Generalized Markup Language (SGML) [Gol90] documents are represented as trees. A node in a document tree may have arbitrarily many children, independent of the symbol at that node. A sequence of documents or subdocuments is called a forest. A main task in do...

Abstract. We propose a construction that augments the precomputation step of a regular tree pattern matching algorithm to include cost analysis. The matching device generated is a pushdown automaton in contrast with the conventionallygenerated tree pattern matching automaton. Our technique can handle a larger class of cost augmented regular tree grammars than can be preprocessed byconventional methods, and has been tested on some input problem instances representing instruction sets for processors. 1

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We propose a new technique for constructing code-generator generators, which combines the advantages of the Graham-Glanville parsing technique and the bottom-up tree parsing approach. Machine descriptions are similar to Yacc specifications. The construction effectively generates a pushdown automaton as the matching device. This device is able to handle ambiguous grammars, and can be used to generate locally optimal code without the use of heuristics. Cost computations are performed at preprocessing time. The class of regular tree grammars augmented with costs that can be handled by our system properly includes those that can be handled by bottom-up systems based on finite-state tree parsing automata. Parsing time is linear in the size of the subject tree. We have tested the system on specifications for some systems and report table sizes.

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