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Abstract

Feature trees have been used to accommodate records in constraint programming and record like structures in computational linguistics. Feature trees model records and subtree selection constraints yield extensible and modular record descriptions. We introduce the constraint system \FEAT\ of ordering constraints interpreted over feature trees. Under the view that feature trees represent symbolic information, the $\leq$-relation corresponds to the information ordering (``carries less information than''). We present a polynomial algorithm that decides the satisfiability of conjunctions of positive and negative information ordering constraints over feature trees. Our results include algorithms for the satisfiability problem and the entailment problem of \FEAT\ in time $O(n^3)$. We also show that \FEAT\ has the independence property (and are thus able to handle negative conjuncts via entailment). Furthermore, we reduce the satisfiability problem of D\"orre's weak-subsumption constraints to the satisfiability problem of \FEAT. This improves the complexity bound for solving weak subsumption constraints from $O(n^5)$ to $O(n^3)$.