A* shortest string decoding for non-idempotent semirings
Abstract
The single shortest path algorithm is undefined for weighted finite-state automata over non-idempotent semirings because such semirings do not guarantee the existence of a shortest path. However, in non-idempotent semirings admitting an order satisfying a monotonicity condition (such as the plus-times or log semirings), the notion of shortest string is well-defined. We describe an algorithm which finds the shortest string for a weighted non-deterministic automaton over such semirings using the backwards shortest distance of an equivalent deterministic automaton (DFA) as a heuristic for A* search performed over a companion idempotent semiring, which is proven to return the shortest string. While there may be exponentially more states in the DFA, this algorithm needs to visit only a small fraction of them if determinization is performed "on the fly".
Keywords
Cite
@article{arxiv.2204.07236,
title = {A* shortest string decoding for non-idempotent semirings},
author = {Kyle Gorman and Cyril Allauzen},
journal= {arXiv preprint arXiv:2204.07236},
year = {2024}
}
Comments
Ten pages, two figures. To appear in the proceedings of the 18th Conference of the European Chapter of the Association for Computational Linguistics