9 research outputs found
Generalized planning: Non-deterministic abstractions and trajectory constraints
We study the characterization and computation of general policies for families of problems that share a structure characterized by a common reduction into a single abstract problem. Policies mu that solve the abstract problem P have been shown to solve all problems Q that reduce to P provided that mu terminates in Q. In this work, we shed light on why this termination condition is needed and how it can be removed. The key observation is that the abstract problem P captures the common structure among the concrete problems Q that is local (Markovian) but misses common structure that is global. We show how such global structure can be captured by means of trajectory constraints that in many cases can be expressed as LTL formulas, thus reducing generalized planning to LTL synthesis. Moreover, for a broad class of problems that involve integer variables that can be increased or decreased, trajectory constraints can be compiled away, reducing generalized planning to fully observable nondeterministic planning
A Correctness Result for Synthesizing Plans With Loops in Stochastic Domains
Finite-state controllers (FSCs), such as plans with loops, are powerful and
compact representations of action selection widely used in robotics, video
games and logistics. There has been steady progress on synthesizing FSCs in
deterministic environments, but the algorithmic machinery needed for lifting
such techniques to stochastic environments is not yet fully understood. While
the derivation of FSCs has received some attention in the context of discounted
expected reward measures, they are often solved approximately and/or without
correctness guarantees. In essence, that makes it difficult to analyze
fundamental concerns such as: do all paths terminate, and do the majority of
paths reach a goal state?
In this paper, we present new theoretical results on a generic technique for
synthesizing FSCs in stochastic environments, allowing for highly granular
specifications on termination and goal satisfaction
On Plans With Loops and Noise
In an influential paper, Levesque proposed a formal specification for
analysing the correctness of program-like plans, such as conditional plans,
iterative plans, and knowledge-based plans. He motivated a logical
characterisation within the situation calculus that included binary sensing
actions. While the characterisation does not immediately yield a practical
algorithm, the specification serves as a general skeleton to explore the
synthesis of program-like plans for reasonable, tractable fragments.
Increasingly, classical plan structures are being applied to stochastic
environments such as robotics applications. This raises the question as to what
the specification for correctness should look like, since Levesque's account
makes the assumption that sensing is exact and actions are deterministic.
Building on a situation calculus theory for reasoning about degrees of belief
and noise, we revisit the execution semantics of generalised plans. The
specification is then used to analyse the correctness of example plans.Comment: Proceedings of AAMAS 201
Generalized Planning as Heuristic Search: A new planning search-space that leverages pointers over objects
Planning as heuristic search is one of the most successful approaches to
classical planning but unfortunately, it does not extend trivially to
Generalized Planning (GP). GP aims to compute algorithmic solutions that are
valid for a set of classical planning instances from a given domain, even if
these instances differ in the number of objects, the number of state variables,
their domain size, or their initial and goal configuration. The generalization
requirements of GP make it impractical to perform the state-space search that
is usually implemented by heuristic planners. This paper adapts the planning as
heuristic search paradigm to the generalization requirements of GP, and
presents the first native heuristic search approach to GP. First, the paper
introduces a new pointer-based solution space for GP that is independent of the
number of classical planning instances in a GP problem and the size of those
instances (i.e. the number of objects, state variables and their domain sizes).
Second, the paper defines a set of evaluation and heuristic functions for
guiding a combinatorial search in our new GP solution space. The computation of
these evaluation and heuristic functions does not require grounding states or
actions in advance. Therefore our GP as heuristic search approach can handle
large sets of state variables with large numerical domains, e.g.~integers.
Lastly, the paper defines an upgraded version of our novel algorithm for GP
called Best-First Generalized Planning (BFGP), that implements a best-first
search in our pointer-based solution space, and that is guided by our
evaluation/heuristic functions for GP.Comment: Under review in the Artificial Intelligence Journal (AIJ
Recolha e conceptualização de experiências de atividades robóticas baseadas em planos para melhoria de competências no longo prazo
Robot learning is a prominent research direction in intelligent robotics. Robotics involves dealing with the issue of integration of multiple technologies, such as sensing, planning, acting, and learning. In robot learning, the long term goal is to develop robots that learn to perform tasks and continuously improve their knowledge and skills through observation and exploration of the environment and interaction with users. While significant research has been performed in the area of learning motor behavior primitives, the topic of learning high-level representations of activities and classes of activities that, decompose into sequences of actions, has not been sufficiently addressed. Learning at the task level is key to increase the robots’ autonomy and flexibility. High-level task knowledge is essential for intelligent robotics since it makes robot programs less dependent on the platform and eases knowledge exchange between robots with different kinematics. The goal of this thesis is to contribute to the development of cognitive robotic capabilities, including supervised experience acquisition through human-robot interaction, high-level task learning from the acquired experiences, and task planning using the acquired task knowledge. A framework containing the required cognitive functions for learning and reproduction of high-level aspects of experiences is proposed. In particular, we propose and formalize the notion of Experience-Based Planning Domains (EBPDs) for long-term learning and planning. A human-robot interaction interface is used to provide a robot with step-by-step instructions on how to perform tasks. Approaches to recording plan-based robot activity experiences including relevant perceptions of the environment and actions taken by the robot are presented. A conceptualization methodology is presented for acquiring task knowledge in the form of activity schemata from experiences. The conceptualization approach is a combination of different techniques including deductive generalization, different forms of abstraction and feature extraction. Conceptualization includes loop detection, scope inference and goal inference. Problem solving in EBPDs is achieved using a two-layer problem solver comprising an abstract planner, to derive an abstract solution for a given task problem by applying a learned activity schema, and a concrete planner, to refine the abstract solution towards a concrete solution. The architecture and the learning and planning methods are applied and evaluated in several real and simulated world scenarios. Finally, the developed learning methods are compared, and conditions where each of them has better applicability are discussed.Aprendizagem de robôs é uma direção de pesquisa proeminente em robótica inteligente. Em robótica, é necessário lidar com a questão da integração de várias tecnologias, como percepção, planeamento, atuação e aprendizagem. Na aprendizagem de robôs, o objetivo a longo prazo é desenvolver robôs que aprendem a executar tarefas e melhoram continuamente os seus conhecimentos e habilidades através da observação e exploração do ambiente e interação com os utilizadores. A investigação tem-se centrado na aprendizagem de comportamentos básicos, ao passo que a aprendizagem de representações de atividades de alto nível, que se decompõem em sequências de ações, e de classes de actividades, não tem sido suficientemente abordada. A aprendizagem ao nível da tarefa é fundamental para aumentar a autonomia e a flexibilidade dos robôs. O conhecimento de alto nível permite tornar o software dos robôs menos dependente da plataforma e facilita a troca de conhecimento entre robôs diferentes. O objetivo desta tese é contribuir para o desenvolvimento de capacidades cognitivas para robôs, incluindo aquisição supervisionada de experiência através da interação humano-robô, aprendizagem de tarefas de alto nível com base nas experiências acumuladas e planeamento de tarefas usando o conhecimento adquirido. Propõe-se uma abordagem que integra diversas funcionalidades cognitivas para aprendizagem e reprodução de aspetos de alto nível detetados nas experiências acumuladas. Em particular, nós propomos e formalizamos a noção de Domínio de Planeamento Baseado na Experiência (Experience-Based Planning Domain, or EBPD) para aprendizagem e planeamento num âmbito temporal alargado. Uma interface para interação humano-robô é usada para fornecer ao robô instruções passo-a-passo sobre como realizar tarefas. Propõe-se uma abordagem para extrair experiências de atividades baseadas em planos, incluindo as percepções relevantes e as ações executadas pelo robô. Uma metodologia de conceitualização é apresentada para a aquisição de conhecimento de tarefa na forma de schemata a partir de experiências. São utilizadas diferentes técnicas, incluindo generalização dedutiva, diferentes formas de abstracção e extração de características. A metodologia inclui detecção de ciclos, inferência de âmbito de aplicação e inferência de objetivos. A resolução de problemas em EBPDs é alcançada usando um sistema de planeamento com duas camadas, uma para planeamento abstrato, aplicando um schema aprendido, e outra para planeamento detalhado. A arquitetura e os métodos de aprendizagem e planeamento são aplicados e avaliados em vários cenários reais e simulados. Finalmente, os métodos de aprendizagem desenvolvidos são comparados e as condições onde cada um deles tem melhor aplicabilidade são discutidos.Programa Doutoral em Informátic