This paper presents a unified solution to the problem of extending stratified DATALOG to express database complexity classes ranging from to; is the query hierarchy containing the decision problems that can be solved in polynomial time by a deterministic Turing machine using a constant number of calls to an -oracle. The solution is based on (i) stratified negation as the core of a simple, declarative semantics for negation, (ii) the use of a “choice” construct to capture the nondeterminism of stable models in a disciplined fashion, (iii) the ability to bind a query to the lowest complexity level that includes the problem at hand, and (iv) a general algorithm that adapts its behavior to the desired level of complexity required by the query so that exponential time computation is only required for hard problems.
Extending Stratified Datalog to Capture Complexity Classes Ranging from P to QH
GRECO, Sergio;SACCA', Domenico;
2001-01-01
Abstract
This paper presents a unified solution to the problem of extending stratified DATALOG to express database complexity classes ranging from to; is the query hierarchy containing the decision problems that can be solved in polynomial time by a deterministic Turing machine using a constant number of calls to an -oracle. The solution is based on (i) stratified negation as the core of a simple, declarative semantics for negation, (ii) the use of a “choice” construct to capture the nondeterminism of stable models in a disciplined fashion, (iii) the ability to bind a query to the lowest complexity level that includes the problem at hand, and (iv) a general algorithm that adapts its behavior to the desired level of complexity required by the query so that exponential time computation is only required for hard problems.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.