Theoretical Computer Science
Finite-state unification automata and relational languages
Information and Computation
Theoretical Computer Science
Handbook of formal languages, vol. 3
Towards Regular Languages over Infinite Alphabets
MFCS '01 Proceedings of the 26th International Symposium on Mathematical Foundations of Computer Science
Finite state machines for strings over infinite alphabets
ACM Transactions on Computational Logic (TOCL)
Two-Variable Logic on Words with Data
LICS '06 Proceedings of the 21st Annual IEEE Symposium on Logic in Computer Science
Alternation-free modal mu-calculus for data trees
LICS '07 Proceedings of the 22nd Annual IEEE Symposium on Logic in Computer Science
Two-variable logic on data trees and XML reasoning
Journal of the ACM (JACM)
Tree acceptors and some of their applications
Journal of Computer and System Sciences
Variable automata over infinite alphabets
LATA'10 Proceedings of the 4th international conference on Language and Automata Theory and Applications
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We introduce variable tree automata with infinite input ranked alphabets. Our model is based on an underlying bottom-up tree automaton over a finite ranked alphabet containing variable symbols. The underlying tree automaton computes its tree language, and then replaces the variable symbols with symbols from the infinite alphabet following certain rules. We show that the class of recognizable tree languages over infinite ranked alphabets is closed under union and intersection but not under complementation. The emptiness problem is decidable, and the equivalence problem is decidable within special subclasses of variable tree automata. The universality problem is also decidable in a subclass of variable tree automata. We demonstrate the robustness of our model by connecting it to variable finite automata and indicating several characterizations of recognizable tree languages over infinite ranked alphabets.