Query evaluation via tree-decompositions
Journal of the ACM (JACM)
Elements Of Finite Model Theory (Texts in Theoretical Computer Science. An Eatcs Series)
Elements Of Finite Model Theory (Texts in Theoretical Computer Science. An Eatcs Series)
On preservation under homomorphisms and unions of conjunctive queries
PODS '04 Proceedings of the twenty-third ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Parameterized Complexity
On preservation under homomorphisms and unions of conjunctive queries
Journal of the ACM (JACM)
ICALP '08 Proceedings of the 35th international colloquium on Automata, Languages and Programming, Part II
European Journal of Combinatorics
Finite model theory on tame classes of structures
MFCS'07 Proceedings of the 32nd international conference on Mathematical Foundations of Computer Science
Boundedness of monadic FO over acyclic structures
ICALP'07 Proceedings of the 34th international conference on Automata, Languages and Programming
Model theory makes formulas large
ICALP'07 Proceedings of the 34th international conference on Automata, Languages and Programming
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A class of relational structures is said to have the extension preservation property if every first-order sentence that is preserved under extensions on the class is equivalent to an existential sentence. The class of all finite structures does not have the extension preservation property. We study the property on classes of finite structures that are better behaved. We show that the property holds of classes of acyclic structures, structures of bounded degree and more generally structures that are wide in a sense we make precise. We also show that the preservation property holds for the class of structures of treewidth at most k, for any k. In contrast, we show that the property fails for the class of planar graphs.