Datalog-Expressibility for Monadic and Guarded Second-Order Logic

@inproceedings{Bodirsky2021DatalogExpressibilityFM,
  title={Datalog-Expressibility for Monadic and Guarded Second-Order Logic},
  author={Manuel Bodirsky and Simon Kn{\"a}uer and Sebastian Rudolph},
  booktitle={ICALP},
  year={2021}
}
We characterise the sentences in Monadic Second-order Logic (MSO) that are over finite structures equivalent to a Datalog program, in terms of an existential pebble game. We also show that for every class C of finite structures that can be expressed in MSO and is closed under homomorphisms, and for all integers l,k, there exists a *canonical* Datalog program Pi of width (l,k), that is, a Datalog program of width (l,k) which is sound for C (i.e., Pi only derives the goal predicate on a finite… 

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