Homomorphism preservation theorems

Published

Journal Article

The homomorphism preservation theorem (h.p.t.), a result in classical model theory, states that a first-order formula is preserved under homomorphisms on all structures (finite and infinite) if and only if it is equivalent to an existential-positive formula. Answering a long-standing question in finite model theory, we prove that the h.p.t. remains valid when restricted to finite structures (unlike many other classical preservation theorems, including the o - Tarski theorem and Lyndon's positivity theorem). Applications of this result extend to constraint satisfaction problems and to database theory via a correspondence between existential-positive formulas and unions of conjunctive queries. A further result of this article strengthens the classical h.p.t.: we show that a first-order formula is preserved under homomorphisms on all structures if and only if it is equivalent to an existential-positive formula of equal quantifier-rank. © 2008 ACM.

Full Text

Duke Authors

Cited Authors

  • Rossman, B

Published Date

  • July 1, 2008

Published In

Volume / Issue

  • 55 / 3

Electronic International Standard Serial Number (EISSN)

  • 1557-735X

International Standard Serial Number (ISSN)

  • 0004-5411

Digital Object Identifier (DOI)

  • 10.1145/1379759.1379763

Citation Source

  • Scopus