The Reactive Engine for Modular Transducers

This paper explains the design of the second release of the Zen toolkit (5-7). It presents a notion of reactive engine which simulates finite-state machines represented as shared aums (8). We show that it yields a modular interpreter for finite state machines described as local transducers. For instance, in the manner of Berry and Sethi, we define a compiler of regular expressions into a scheduler for the reactive engine, chaining through aums labeled with phases — associated with the letters of the regular expression. This gives a modular composition scheme for general finite-state machines. Many variations of this basic idea may be put to use according to cir- constances. The simplest one is when aums are reduced to dictionaries, i.e. to (minimalized) acyclic deterministic automata recognizing finite languages. Then one may proceed to adding supplementary structure to the aum algebra, namely non-determinism, loops, and transduction. Such additional choice points require fitting some additional control to the reactive engine. Further parameters are required for some functional- ities. For instance, the local word access stack is handy as an argument to the output routine in the case of transducers. Internal virtual addresses demand the full local state access stack for their interpretation. A characteristic example is provided, it gives a complete analyser for compound substantives. It is an abstraction from a modular version of the Sanskrit segmenter presented in (9). This improved segmenter uses a regular relation condition relating the phases of morphology genera- tion, and enforcing the correct geometry of morphemes. Thus we obtain compound nouns from iic*.(noun+iic.ifc), where iic and ifc are the re- spectively prefix and sux substantival forms for compound formation.