Cost register automata (CRA) and its subclass, copyless CRA, were recently proposed by Alur et al. as a new model for computing functions over words. We study the expressiveness and closure properties of copyless CRA. In particular we compare this model with the well-know model of weighted automata.
Weighted automata can be naturally characterized by a subfragment of weighted logic, a quantitative extension of MSO introduced by Droste and Gastin. Our results show that a similar characterization of copyless CRA seems to be unlikely. We introduce a new quantitative logic, which turns out to be equally expressive to a natural subclass of copyless CRA.
Based on joint work with Cristian Riveros.