7 research outputs found
Learning-Based Synthesis of Safety Controllers
We propose a machine learning framework to synthesize reactive controllers
for systems whose interactions with their adversarial environment are modeled
by infinite-duration, two-player games over (potentially) infinite graphs. Our
framework targets safety games with infinitely many vertices, but it is also
applicable to safety games over finite graphs whose size is too prohibitive for
conventional synthesis techniques. The learning takes place in a feedback loop
between a teacher component, which can reason symbolically about the safety
game, and a learning algorithm, which successively learns an overapproximation
of the winning region from various kinds of examples provided by the teacher.
We develop a novel decision tree learning algorithm for this setting and show
that our algorithm is guaranteed to converge to a reactive safety controller if
a suitable overapproximation of the winning region can be expressed as a
decision tree. Finally, we empirically compare the performance of a prototype
implementation to existing approaches, which are based on constraint solving
and automata learning, respectively
Optimal Strategies in Pushdown Reachability Games
An algorithm for computing optimal strategies in pushdown reachability games was given by Cachat. We show that the information tracked by this algorithm is too coarse and the strategies constructed are not necessarily optimal. We then show that the algorithm can be refined to recover optimality. Through a further non-trivial argument the refined algorithm can be run in 2EXPTIME by bounding the play-lengths tracked to those that are at most doubly exponential. This is optimal in the sense that there exists a game for which the optimal strategy requires a doubly exponential number of moves to reach a target configuration
Reverse engineering queries in ontology-enriched systems: the case of expressive horn description logic ontologies
We introduce the query-by-example (QBE) paradigm for query answering in the presence of ontologies. Intuitively, QBE permits non-expert users to explore the data by providing examples of the information they (do not) want, which the system then generalizes into a query. Formally, we study the following question: given a knowledge base and sets of positive and negative examples, is there a query that returns all positive but none of the negative examples? We focus on description logic knowledge bases with ontologies formulated in Horn-ALCI and (unions of) conjunctive queries. Our main contributions are characterizations, algorithms and tight complexity bounds for QBE
Solving Infinite Games in the Baire Space
Infinite games (in the form of Gale-Stewart games) are studied where a play
is a sequence of natural numbers chosen by two players in alternation, the
winning condition being a subset of the Baire space . We
consider such games defined by a natural kind of parity automata over the
alphabet , called -MSO-automata, where transitions are
specified by monadic second-order formulas over the successor structure of the
natural numbers. We show that the classical B\"uchi-Landweber Theorem (for
finite-state games in the Cantor space ) holds again for the present
games: A game defined by a deterministic parity -MSO-automaton is
determined, the winner can be computed, and an -MSO-transducer
realizing a winning strategy for the winner can be constructed.Comment: Minor revision. 26 pages, 1 figur