On notions of regularity for data languages

Motivated by considerations in XML theory and model checking, data strings have been introduced as, an extension of finite alphabet strings which carry, at each position, a symbol and a data value from an infinite domain. Previous work has shown that it is not easy to come up with an expressive yet decidable automata model for data languages. Recently, such an automata model, data automata, was introduced. This paper introduces a simpler but equivalent model and investigates its expressive power, algorithmic and closure properties and some extensions.