To add another one: Lucene uses a finite state transducer to represent a part of its term index: <a href="http:&#x2F;&#x2F;blog.mikemccandless.com&#x2F;2010&#x2F;12&#x2F;using-finite-state-transducers-in.html" rel="nofollow">http:&#x2F;&#x2F;blog.mikemccandless.com&#x2F;2010&#x2F;12&#x2F;using-finite-state-tr...</a> --- It&#x27;s essentially a dictionary as you say, but instead of a direct NLP use case, it might map a word to some numerical value (like a file offset where the term&#x27;s postings list resides).<p>I actually haven&#x27;t been able to find anyone else using transducers for this purpose (sans OpenSextant, I think), but I&#x27;d be curious to hear about it if others knew. It seems like a really awesome way to represent nearly arbitrary maps&#x2F;sets of billions of strings.