154 research outputs found
The CIFF Proof Procedure for Abductive Logic Programming with Constraints: Theory, Implementation and Experiments
We present the CIFF proof procedure for abductive logic programming with
constraints, and we prove its correctness. CIFF is an extension of the IFF
proof procedure for abductive logic programming, relaxing the original
restrictions over variable quantification (allowedness conditions) and
incorporating a constraint solver to deal with numerical constraints as in
constraint logic programming. Finally, we describe the CIFF system, comparing
it with state of the art abductive systems and answer set solvers and showing
how to use it to program some applications. (To appear in Theory and Practice
of Logic Programming - TPLP)
A New Rational Algorithm for View Updating in Relational Databases
The dynamics of belief and knowledge is one of the major components of any
autonomous system that should be able to incorporate new pieces of information.
In order to apply the rationality result of belief dynamics theory to various
practical problems, it should be generalized in two respects: first it should
allow a certain part of belief to be declared as immutable; and second, the
belief state need not be deductively closed. Such a generalization of belief
dynamics, referred to as base dynamics, is presented in this paper, along with
the concept of a generalized revision algorithm for knowledge bases (Horn or
Horn logic with stratified negation). We show that knowledge base dynamics has
an interesting connection with kernel change via hitting set and abduction. In
this paper, we show how techniques from disjunctive logic programming can be
used for efficient (deductive) database updates. The key idea is to transform
the given database together with the update request into a disjunctive
(datalog) logic program and apply disjunctive techniques (such as minimal model
reasoning) to solve the original update problem. The approach extends and
integrates standard techniques for efficient query answering and integrity
checking. The generation of a hitting set is carried out through a hyper
tableaux calculus and magic set that is focused on the goal of minimality.Comment: arXiv admin note: substantial text overlap with arXiv:1301.515
Negative non-ground queries in well founded semantics
Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Computational LogicThe existing implementations of Well Founded Semantics restrict or forbid the use of
variables when using negative queries, something which is essential for using logic
programming as a programming language.
We present a procedure to obtain results under the Well Founded Semantics that
removes this constraint by combining two techniques: the transformation presented
in [MMNMH08] to obtain from a program its dual and the derivation procedure presented
in [PAP+91] to determine if a query belongs or not to the Well Founded Model
of a program.
Some problems arise during their combination, mainly due to the original environment
for which each one was designed: results obtained in the first one obey a
variant of Kunen Semantics and non-ground programs are not allowed (or previously
grounded) in the second one.
Most of these problems were solved by using abductive techniques, which lead
us to observe that the existing implementations of abduction in logic programming
disallow the use of variables.
The reason for that is the impossibility to evaluate non-ground queries, so it
seemed interesting to develop an abductive framework making use of our negation
system.
Both goals are achieved in this thesis: the capability of solving non-ground queries
under Well Founded Semantics and the use of variables in abductive logic programming
Logical settings for concept learning from incomplete examples in First Order Logic
We investigate here concept learning from incomplete examples. Our first
purpose is to discuss to what extent logical learning settings have to be
modified in order to cope with data incompleteness. More precisely we are
interested in extending the learning from interpretations setting introduced by
L. De Raedt that extends to relational representations the classical
propositional (or attribute-value) concept learning from examples framework. We
are inspired here by ideas presented by H. Hirsh in a work extending the
Version space inductive paradigm to incomplete data. H. Hirsh proposes to
slightly modify the notion of solution when dealing with incomplete examples: a
solution has to be a hypothesis compatible with all pieces of information
concerning the examples. We identify two main classes of incompleteness. First,
uncertainty deals with our state of knowledge concerning an example. Second,
generalization (or abstraction) deals with what part of the description of the
example is sufficient for the learning purpose. These two main sources of
incompleteness can be mixed up when only part of the useful information is
known. We discuss a general learning setting, referred to as "learning from
possibilities" that formalizes these ideas, then we present a more specific
learning setting, referred to as "assumption-based learning" that cope with
examples which uncertainty can be reduced when considering contextual
information outside of the proper description of the examples. Assumption-based
learning is illustrated on a recent work concerning the prediction of a
consensus secondary structure common to a set of RNA sequences
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