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キーワード:
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要旨:
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 $O(n^3)$.
