On the Enumeration Complexity of Unions of Conjunctive Queries

@article{Carmeli2019OnTE,
  title={On the Enumeration Complexity of Unions of Conjunctive Queries},
  author={Nofar Carmeli and Markus Kr{\"o}ll},
  journal={Proceedings of the 38th ACM SIGMOD-SIGACT-SIGAI Symposium on Principles of Database Systems},
  year={2019}
}
  • Nofar Carmeli, Markus Kröll
  • Published 2019
  • Computer Science
  • Proceedings of the 38th ACM SIGMOD-SIGACT-SIGAI Symposium on Principles of Database Systems
We study the enumeration complexity of Unions of Conjunctive Queries (UCQs). We aim to identify the UCQs that are tractable in the sense that the answer tuples can be enumerated with a linear preprocessing phase and a constant delay between every successive tuples. It has been established that, in the absence of self joins and under conventional complexity assumptions, the CQs that admit such an evaluation are precisely the free-connex ones. A union of tractable CQs is always tractable. We… Expand
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