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SemiInflationary DATALOG: A Declarative Database Language with Procedural Features
"... This paper presents a rulebased database language which extends stratified DATALOG by adding a controlled form of inflationary fixpoint, immersed in a context of classical stratified negation with least fixpoint. The proposed language, called SemiInflationary DATALOG (DATALOG for short), smooth ..."
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This paper presents a rulebased database language which extends stratified DATALOG by adding a controlled form of inflationary fixpoint, immersed in a context of classical stratified negation with least fixpoint. The proposed language, called SemiInflationary DATALOG (DATALOG for short), smoothly combines the declarative purity of stratified negation with the procedural style of the inflationary fixpoint, in a mixed style: declarative rules, whenever it is natural and convenient, and procedural ones, any time it is easier to list the sequence of single actions. In the latter case, in order not to oblige the programmer to supply unnecessary procedural details, a number of choice constructs are available to express don't care nondeterminism. The semantics of a DATALOG @(*) program is given using stable models by means of rule rewriting into a DATALOG program with choice and XYstratification. In addition the complexity and expressive power of DATALOG @(*) queries is precisely characterized and some lights are put on the related class NQPTIME as well
Multivalued Functions: Turing Characterizations and Complexity Results
"... This paper presents a nice Turing characterization of important classes of multivalued functions (used to model search problems) which elucidates properties of such classes as well as relationships among them. The results are based on a Turing transducer, called writenondeterministic (WND) tran ..."
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This paper presents a nice Turing characterization of important classes of multivalued functions (used to model search problems) which elucidates properties of such classes as well as relationships among them. The results are based on a Turing transducer, called writenondeterministic (WND) transducer, which extends deterministic Turing machines with a simple nondeterministic construct which leaves track of each guess on the output tape. Moreover, the paper
On PolynomialTime Computable NonDeterministic Queries
, 1999
"... A search problem is typically modeled by a multivalued function, say M , since any problem instance has in general many solutions. However, when answering a problem, we are usually interested in obtaining just one of its solutions; therefore, we replace M with a singlevalued function F "r ..."
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A search problem is typically modeled by a multivalued function, say M , since any problem instance has in general many solutions. However, when answering a problem, we are usually interested in obtaining just one of its solutions; therefore, we replace M with a singlevalued function F "rening" it, i.e., F has the same domain as M and, for each input X, F (X) is an element of M(X). A nondeterministic query is a "generic" multivalued function from the family of databases on B to the family of all relations on R, where B and R are the schemes of a database and of a relation, respectively. Desirable classes of nondeterministic queries are those that can be rened by a polynomialtime singlevalued functions: we say that the queries in such classes are polynomialtime computable. An important class of polynomialtime computable nondeterministic queries is NQPTIME, that is the class of all queries computed by polynomial time transducers such that for each input, each ...