The complexity of containment and satisfiability of conjunctive queries over finite, unranked, labeled trees is studied with respect to the axes Child, NextSibling, their transitive and reflexive closures, and Following. For the containment problem a trichotomy is presented, classifying the problems as in PTIME, coNP-complete, or Π P 2 -complete. For the satisfiability problem most problems are classified as either in PTIME or NP-complete.
REF studied containment of conjunctive queries over tree-structured data and and proved a trichotomy, classifying the problems as in PTIME, CONP-complete, or Π p 2 -complete.
Conjunctive query containment over trees
In 11th International Symposium on Database Programming Languages (DBPL
Mathematics Computer Science