9 research outputs found
Symmetry Breaking for Answer Set Programming
In the context of answer set programming, this work investigates symmetry
detection and symmetry breaking to eliminate symmetric parts of the search
space and, thereby, simplify the solution process. We contribute a reduction of
symmetry detection to a graph automorphism problem which allows to extract
symmetries of a logic program from the symmetries of the constructed coloured
graph. We also propose an encoding of symmetry-breaking constraints in terms of
permutation cycles and use only generators in this process which implicitly
represent symmetries and always with exponential compression. These ideas are
formulated as preprocessing and implemented in a completely automated flow that
first detects symmetries from a given answer set program, adds
symmetry-breaking constraints, and can be applied to any existing answer set
solver. We demonstrate computational impact on benchmarks versus direct
application of the solver.
Furthermore, we explore symmetry breaking for answer set programming in two
domains: first, constraint answer set programming as a novel approach to
represent and solve constraint satisfaction problems, and second, distributed
nonmonotonic multi-context systems. In particular, we formulate a
translation-based approach to constraint answer set solving which allows for
the application of our symmetry detection and symmetry breaking methods. To
compare their performance with a-priori symmetry breaking techniques, we also
contribute a decomposition of the global value precedence constraint that
enforces domain consistency on the original constraint via the unit-propagation
of an answer set solver. We evaluate both options in an empirical analysis. In
the context of distributed nonmonotonic multi-context system, we develop an
algorithm for distributed symmetry detection and also carry over
symmetry-breaking constraints for distributed answer set programming.Comment: Diploma thesis. Vienna University of Technology, August 201
Contextual and Possibilistic Reasoning for Coalition Formation
In multiagent systems, agents often have to rely on other agents to reach
their goals, for example when they lack a needed resource or do not have the
capability to perform a required action. Agents therefore need to cooperate.
Then, some of the questions raised are: Which agent(s) to cooperate with? What
are the potential coalitions in which agents can achieve their goals? As the
number of possibilities is potentially quite large, how to automate the
process? And then, how to select the most appropriate coalition, taking into
account the uncertainty in the agents' abilities to carry out certain tasks? In
this article, we address the question of how to find and evaluate coalitions
among agents in multiagent systems using MCS tools, while taking into
consideration the uncertainty around the agents' actions. Our methodology is
the following: We first compute the solution space for the formation of
coalitions using a contextual reasoning approach. Second, we model agents as
contexts in Multi-Context Systems (MCS), and dependence relations among agents
seeking to achieve their goals, as bridge rules. Third, we systematically
compute all potential coalitions using algorithms for MCS equilibria, and given
a set of functional and non-functional requirements, we propose ways to select
the best solutions. Finally, in order to handle the uncertainty in the agents'
actions, we extend our approach with features of possibilistic reasoning. We
illustrate our approach with an example from robotics
Abstract Modular Inference Systems and Solvers
Integrating diverse formalisms into modular knowledge representation systems offers increased expressivity, modeling convenience and computational benefits. We introduce the concepts of abstract inference modules and abstract modular inference systems to study general principles behind the design and analysis of model-generating programs, or solvers, for integrated multilogic systems.We show how modules and modular systems give rise to transition graphs, which are a natural and convenient representation of solvers, an idea pioneered by the SAT community. We illustrate our approach by showing how it applies to answer-set programming and propositional logic, and to multi-logic systems based on these two formalisms
On Abstract Modular Inference Systems and Solvers
Integrating diverse formalisms into modular knowledge representation systems offers increased expressivity, modeling convenience, and computational benefits. We introduce the concepts of abstract inference modules and abstract modular inference systems to study general principles behind the design and analysis of model generating programs, or solvers, for integrated multi-logic systems. We show how modules and modular systems give rise to transition graphs, which are a natural and convenient representation of solvers, an idea pioneered by the SAT community. These graphs lend themselves well to extensions that capture such important solver design features as learning. In the paper, we consider two flavors of learning for modular formalisms, local and global. We illustrate our approach by showing how it applies to answer set programming, propositional logic, multi-logic systems based on these two formalisms and, more generally, to satisfiability modulo theories
Arithmetic and Modularity in Declarative Languages for Knowledge Representation
The past decade has witnessed the development of many important declarative languages for knowledge representation and reasoning such as answer set programming (ASP) languages and languages that extend first-order logic. Also, since these languages depend on background solvers, the recent advancements in the efficiency of solvers has positively affected the usability of such languages. This thesis studies extensions of knowledge representation (KR) languages with arithmetical operators and methods to combine different KR languages. With respect to arithmetic in declarative KR languages, we show that existing KR languages suffer from a huge disparity between their expressiveness and their computational power. Therefore, we develop an ideal KR language that captures the complexity class NP for arithmetical search problems and guarantees universality and efficiency for solving such problems. Moreover, we introduce a framework to language-independently combine modules from different KR languages. We study complexity and expressiveness of our framework and develop algorithms to solve modular systems. We define two semantics for modular systems based on (1) a model-theoretical view and (2) an operational view on modular systems. We prove that our two semantics coincide and also develop mechanisms to approximate answers to modular systems using the operational view. We augment our algorithm these approximation mechanisms to speed up the process of solving modular system. We further generalize our modular framework with supported model semantics that disallows self-justifying models. We show that supported model semantics generalizes our two previous model-theoretical and operational semantics. We compare and contrast the expressiveness of our framework under supported model semantics with another framework for interlinking knowledge bases, i.e., multi-context systems, and prove that supported model semantics generalizes and unifies different semantics of multi-context systems. Motivated by the wide expressiveness of supported models, we also define a new supported equilibrium semantics for multi-context systems and show that supported equilibrium semantics generalizes previous semantics for multi-context systems. Furthermore, we also define supported semantics for propositional programs and show that supported model semnatics generalizes the acclaimed stable model semantics and extends the two celebrated properties of rationality and minimality of intended models beyond the scope of logic programs
Anales del XIII Congreso Argentino de Ciencias de la Computaci贸n (CACIC)
Contenido:
Arquitecturas de computadoras
Sistemas embebidos
Arquitecturas orientadas a servicios (SOA)
Redes de comunicaciones
Redes heterog茅neas
Redes de Avanzada
Redes inal谩mbricas
Redes m贸viles
Redes activas
Administraci贸n y monitoreo de redes y servicios
Calidad de Servicio (QoS, SLAs)
Seguridad inform谩tica y autenticaci贸n, privacidad
Infraestructura para firma digital y certificados digitales
An谩lisis y detecci贸n de vulnerabilidades
Sistemas operativos
Sistemas P2P
Middleware
Infraestructura para grid
Servicios de integraci贸n (Web Services o .Net)Red de Universidades con Carreras en Inform谩tica (RedUNCI
Anales del XIII Congreso Argentino de Ciencias de la Computaci贸n (CACIC)
Contenido:
Arquitecturas de computadoras
Sistemas embebidos
Arquitecturas orientadas a servicios (SOA)
Redes de comunicaciones
Redes heterog茅neas
Redes de Avanzada
Redes inal谩mbricas
Redes m贸viles
Redes activas
Administraci贸n y monitoreo de redes y servicios
Calidad de Servicio (QoS, SLAs)
Seguridad inform谩tica y autenticaci贸n, privacidad
Infraestructura para firma digital y certificados digitales
An谩lisis y detecci贸n de vulnerabilidades
Sistemas operativos
Sistemas P2P
Middleware
Infraestructura para grid
Servicios de integraci贸n (Web Services o .Net)Red de Universidades con Carreras en Inform谩tica (RedUNCI