The Logic of Counting Query Answers
summary
A logic called sharp logic is defined that outputs a numeric value for a formula on a finite structure and supports casting first‑order formulas, projection, multiplication, addition and integer constants; bounded width evaluation runs in polynomial time. A dichotomy is proved for existential positive queries: fixed‑parameter tractability holds iff the query compiles to a bounded‑width sharp logic representation. An algorithm uses inclusion–exclusion to normalize, applies width minimization (computable), and relies on an independence theorem showing linear independence of homomorphism‑count vectors.
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chapters (8)
- 0:00Intro
- 0:28Query evaluation
- 3:15Studying complexity
- 5:33Parameterized complexity
- 7:13Classification
- 17:12Example
- 18:56Width minimization
- 24:23Open issues
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