A conjunctive query problem in relational database theory is a problem to determine whether or not a tuple belongs to the answer of a conjunctive query over a database. Here, a tuple and a conjunctive query are regarded as a ground atom and a nonrecursive function-free definite clause, respectively. While the conjunctive query problem is NP-complete in general, it becomes efficiently solvable if a conjunctive query is acyclic. Concerned with this problem, we investigate the learnability of acyclic conjunctive queries from an instance with a j-database which is a finite set of ground unit clauses containing at most j-ary predicate symbols. We deal with two kinds of instances, a simple instance as a set of ground atoms and an extended instance as a set of pairs of a ground atom and a description. Then, we show that, for each j ≥ 3, there exist a j-database such that acyclic conjunctive queries are not polynomially predictable from an extended instance under the cryptographic assumptions. Also we show that, for each n > 0 and a polynomial p, there exists a p(n)-database of size O(2p(n)) such that predicting Boolean formulae of size p(n) over n variables reduces to predicting acyclic conjunctive queries from a simple instance. This result implies that, if we can ignore the size of a database, then acyclic conjunctive queries are not polynomially predictable from a simple instance under the cryptographic assumptions. Finally, we show that, if either j = 1, or j = 2 and the number of element of a database is at most l (≥ 0), then acyclic conjunctive queries are paclearnable from a simple instance with j-databases.
CITATION STYLE
Hirata, K. (2000). On the hardness of learning acyclic conjunctive queries. In Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) (Vol. 1968, pp. 238–251). Springer Verlag. https://doi.org/10.1007/3-540-40992-0_18
Mendeley helps you to discover research relevant for your work.