Modal logic
Computers and Intractability: A Guide to the Theory of NP-Completeness
Computers and Intractability: A Guide to the Theory of NP-Completeness
Verifying lossy channel systems has nonprimitive recursive complexity
Information Processing Letters
What You Always Wanted to Know About Datalog (And Never Dared to Ask)
IEEE Transactions on Knowledge and Data Engineering
Secure XML querying with security views
SIGMOD '04 Proceedings of the 2004 ACM SIGMOD international conference on Management of data
Efficient algorithms for processing XPath queries
ACM Transactions on Database Systems (TODS)
The expressivity of XPath with transitive closure
Proceedings of the twenty-fifth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Frontiers of tractability for typechecking simple XML transformations
Journal of Computer and System Sciences
Efficient algorithms for processing XPath queries
VLDB '02 Proceedings of the 28th international conference on Very Large Data Bases
XPath satisfiability in the presence of DTDs
Journal of the ACM (JACM)
XPath, transitive closure logic, and nested tree walking automata
Proceedings of the twenty-seventh ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
LTL with the freeze quantifier and register automata
ACM Transactions on Computational Logic (TOCL)
Two-variable logic on data trees and XML reasoning
Journal of the ACM (JACM)
Satisfiability of downward XPath with data equality tests
Proceedings of the twenty-eighth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Future-Looking Logics on Data Words and Trees
MFCS '09 Proceedings of the 34th International Symposium on Mathematical Foundations of Computer Science 2009
Forward-XPath and extended register automata on data-trees
Proceedings of the 13th International Conference on Database Theory
A Decidable Two-Way Logic on Data Words
LICS '11 Proceedings of the 2011 IEEE 26th Annual Symposium on Logic in Computer Science
Satisfiability of XPath queries with sibling axes
DBPL'05 Proceedings of the 10th international conference on Database Programming Languages
First order paths in ordered trees
ICDT'05 Proceedings of the 10th international conference on Database Theory
On XPath with transitive axes and data tests
Proceedings of the 32nd symposium on Principles of database systems
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We investigate the satisfiability problem for downward-XPath, the fragment of XPath that includes the child and descendant axes, and tests for (in)equality of attributes’ values. We prove that this problem is decidable, EXPTIME-complete. These bounds also hold when path expressions allow closure under the Kleene star operator. To obtain these results, we introduce a Downward Data automata model (DD automata) over trees with data, which has a decidable emptiness problem. Satisfiability of downward-XPath can be reduced to the emptiness problem of DD automata and hence its decidability follows. Although downward-XPath does not include any horizontal axis, DD automata are more expressive and can perform some horizontal tests. Thus, we show that the satisfiability remains in EXPTIME even in the presence of the regular constraints expressible by DD automata. However, the same problem in the presence of any regular constraint is known to have a nonprimitive recursive complexity. Finally, we give the exact complexity of the satisfiability problem for several fragments of downward-XPath.