Unification of concept terms in description logics
Journal of Symbolic Computation
Automata theory for XML researchers
ACM SIGMOD Record
The Complexity of Set Constraints
CSL '93 Selected Papers from the 7th Workshop on Computer Science Logic
Rewriting for Cryptographic Protocol Verification
CADE-17 Proceedings of the 17th International Conference on Automated Deduction
Query Evaluation on Compressed Trees (Extended Abstract)
LICS '03 Proceedings of the 18th Annual IEEE Symposium on Logic in Computer Science
Unification Modulo ACUI Plus Distributivity Axioms
Journal of Automated Reasoning
Computation: finite and infinite machines
Computation: finite and infinite machines
Path queries on compressed XML
VLDB '03 Proceedings of the 29th international conference on Very large data bases - Volume 29
Tree Automata with Global Constraints
DLT '08 Proceedings of the 12th international conference on Developments in Language Theory
LATA '09 Proceedings of the 3rd International Conference on Language and Automata Theory and Applications
Recognition of a Spanning Tree of Directed Acyclic Graphs by Tree Automata
CIAA '09 Proceedings of the 14th International Conference on Implementation and Application of Automata
Finite automata on unranked and unordered DAGs
DLT'07 Proceedings of the 11th international conference on Developments in language theory
Recognition of directed acyclic graphs by spanning tree automata
Theoretical Computer Science
Rigid tree automata and applications
Information and Computation
The parameterized complexity of chosen problems for finite automata on trees
LATA'11 Proceedings of the 5th international conference on Language and automata theory and applications
Tree automata and XPath on compressed trees
CIAA'05 Proceedings of the 10th international conference on Implementation and Application of Automata
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Tree automata are widely used in various contexts. They are closed under boolean operations and their emptiness problem is decidable in polynomial time. Dag automata are natural extensions of tree automata, operating on dags instead of on trees; they can also be used for solving problems. Our purpose in this paper is to show that algebraically they behave differently: the class of dag automata is not closed under complementation, dag automata are not determinizable, their membership problem is NP-complete, the universality problem is undecidable, and the emptiness problem is NP-complete even for deterministic labeled dag automata.