Query Evaluation on Compressed Trees (Extended Abstract).

This paper studies the problem of evaluating unary (or node-selecting)queries on unranked trees compressed in a naturalstructure-preserving way, by the sharing of common subtrees. Themotivation to study unary queries on unranked trees comes fromthe database field, where querying XML documents, which can beconsidered as unranked labelled trees, is an important task.We give algorithms and complexity results for the evaluationof XPath and monadic datalog queries. Furthermore, we proposea new automata-theoretic formalism for querying trees and givealgorithms for evaluating queries defined by such automata.