Showing papers by "Giuseppe De Giacomo published in 2015"

Synthesis for LTL and LDL on finite traces

Abstract: In this paper, we study synthesis from logical specifications over finite traces expressed in LTLf and its extension LDLf. Specifically, in this form of synthesis, propositions are partitioned in controllable and uncontrollable ones, and the synthesis task consists of setting the controllable propositions over time so that, in spite of how the value of the uncontrollable ones changes, the specification is fulfilled. Conditional planning in presence of declarative and procedural trajectory constraints is a special case of this form of synthesis. We characterize the problem computationally as 2EXPTIME-complete and present a sound and complete synthesis technique based on DFA (reachability) games.

Declarative Process Modeling in BPMN

Abstract: Traditional business process modeling notations, including the standard Business Process Model and Notation (BPMN), rely on an imperative paradigm wherein the process model captures all allowed activity flows. In other words, every flow that is not specified is implicitly disallowed. In the past decade, several researchers have exposed the limitations of this paradigm in the context of business processes with high variability. As an alternative, declarative process modeling notations have been proposed (e.g., Declare). These notations allow modelers to capture constraints on the allowed activity flows, meaning that all flows are allowed provided that they do not violate the specified constraints. Recently, it has been recognized that the boundary between imperative and declarative process modeling is not crisp. Instead, mixtures of declarative and imperative process modeling styles are sometimes preferable, leading to proposals for hybrid process modeling notations. These developments raise the question of whether completely new notations are needed to support hybrid process modeling. This paper answers this question negatively. The paper presents a conservative extension of BPMN for declarative process modeling, namely BPMN-D, and shows that Declare models can be transformed into readable BPMN-D models.

Bounded Situation Calculus Action Theories

Abstract: In this paper, we investigate bounded action theories in the situation calculus. A bounded action theory is one which entails that, in every situation, the number of object tuples in the extension of fluents is bounded by a given constant, although such extensions are in general different across the infinitely many situations. We argue that such theories are common in applications, either because facts do not persist indefinitely or because the agent eventually forgets some facts, as new ones are learnt. We discuss various classes of bounded action theories. Then we show that verification of a powerful first-order variant of the mu-calculus is decidable for such theories. Notably, this variant supports a controlled form of quantification across situations. We also show that through verification, we can actually check whether an arbitrary action theory maintains boundedness.

Data Complexity of Query Answering in Description Logics (Extended Abstract)

Abstract: We study the data complexity of answering conjunctive queries over Description Logic knowledge bases constituted by a TBox and an ABox. In particular, we are interested in characterizing the FOrewritability and the polynomial tractability boundaries of conjunctive query answering, depending on the expressive power of the DL used to express the knowledge base. What emerges from our complexity analysis is that the Description Logics of the DL-Lite family are essentially the maximal logics allowing for conjunctive query answering through standard database technology.

Knowledge representation and reasoning: what's hot

Abstract: This is an extended abstract about what is hot in the field of Knowledge Representation and Reasoning.

Description logic based dynamic systems: modeling, verification, and synthesis

Abstract: In this paper, we overview the recently introduced general framework of Description Logic Based Dynamic Systems, which leverages Levesque's functional approach to model systems that evolve the extensional part of a description logic knowledge base by means of actions. This framework is parametric w.r.t. the adopted description logic and the progression mechanism. In this setting, we discuss verification and adversarial synthesis for specifications expressed in a variant of first-order µ-calculus, with a controlled form of quantification across successive states and present key decidability results under the natural assumption of state-boundedness.

Service Composition with PDDL Representations and Visualization over Videogame Engines (Short Paper)

Abstract: We devise a succinct knowledge representation framework based on a nondeterministic variant of a well-known Artificial Intelligence formalism, called PDDL, for representing dynamic domains in Planning. We represent the environment and the agents' (high-level) behavior as distinct PDDL action domains and exploit service composition techniques, to compose agent behaviors so as to realize a collective behavior of interest to the user. Specifically, we characterize the computational complexity of the problem and give effective algorithms for solving it, taking advantage of the succinct representation in PDDL. We explore the visualization of service composition over this framework based on the videogame metaphor of virtual worlds using a popular engine. The execution then of agents as game characters provides a form of procedural attachment of atomic actions to concrete interactions within a realistic 3D space.

On the undecidability of the situation calculus extended with description logic ontologies

Abstract: In this paper we investigate situation calculus action theories extended with ontologies, expressed as description logics TBoxes that act as state constraints. We show that this combination, while natural and desirable, is particularly problematic: it leads to undecidability of the simplest form of reasoning, namely satisfiability, even for the simplest kinds of description logics and the simplest kind of situation calculus action theories.

Synchronous Games in the Situation Calculus (Extended Abstract)

Abstract: We develop a situation calculus-based account of multi-player synchronous games. These are represented as action theories called situation calculus synchronous game structures (SCSGSs) that involve a single action tick whose eects depend on the combination of moves chosen by the players. Properties of games, e.g., winning conditions, playability, weak and strong winnability, etc. can be expressed in a rst-order variant of alternating-time mu-calculus. Computationally eective verication can be performed. SCSGSs can be viewed as a variant of the Game Description Language (GDL) where states are represented by rst-order theories.

Synchronous Games in the Situation Calculus

Abstract: We develop a situation calculus-based account of multi-player synchronous games. These are represented as action theories called situation calculus synchronous game structures (SCSGSs) that involve a single action tick whose effects depend on the combination of moves chosen by the players. Properties of games, e.g., winning conditions, playability, weak and strong winnability, etc. can be expressed in a first-order variant of alternating-time mu-calculus. Computationally effective verification can be performed. SCSGSs can be viewed as a variant of the Game Description Language (GDL) where states are represented by first-order theories.

Adding DL-Lite TBoxes to Proper Knowledge Bases

Abstract: Levesque's proper knowledge bases proper KBs correspond to infinite sets of ground positive and negative facts, with the notable property that for FOL formulas in a certain normal form, which includes conjunctive queries and positive queries possibly extended with a controlled form of negation, entailment reduces to formula evaluation. However proper KBs represent extensional knowledge only. In description logic terms, they correspond to ABoxes. In this paper, we augment them with DL-Lite TBoxes, expressing intensional knowledge i.e., the ontology of the domain. DL-Lite has the notable property that conjunctive query answering over TBoxes and standard description logic ABoxes is reducible to formula evaluation over the ABox only. Here, we investigate whether such a property extends to ABoxes consisting of proper KBs. Specifically, we consider two DL-Lite variants: $$\textit{DL-Lite}_{ rdfs }$$, roughly corresponding to RDFS, and $$\textit{DL-Lite}_{ core }$$, roughly corresponding to OWL 2 QL. We show that when a $$\textit{DL-Lite}_{ rdfs }$$ TBox is coupled with a proper KB, the TBox can be compiled away, reducing query answering to evaluation on the proper KB alone. But this reduction is no longer possible when we associate proper KBs with $$\textit{DL-Lite}_{ core }$$ TBoxes. Indeed, we show that in the latter case, query answering even for conjunctive queries becomes coNP-hard in data complexity.

Temporal Reasoning in Bounded Situation Calculus

Abstract: In this talk, we survey recent results on situation calculus bounded action theories. These are action theories with the constraints that the size of the extension of fluents in every situation must be bounded, though such an extension changes from situation to situation. Such action theories give rise to infinite transition systems that can be faithfully abstracted into finite ones, making verification decidable.

Fixpoint Node Selection Query Languages for Trees

Abstract: The study of node selection query languages for (finite) trees has been a major topic in the recent research on query languages for Web documents. On one hand, there has been an extensive study of XPath and its various extensions. On the other hand, query languages based on classical logics, such as first-order logic (FO) or Monadic Second-Order Logic (MSO), have been considered. Results in this area typically relate an XPath-based language to a classical logic. What has yet to emerge is an XPath-related language that is as expressive as MSO, and at the same time enjoys the computational properties of XPath, which are linear time query evaluation and exponential time query-containment test. In this paper we propose muXPath, which is the alternation-free fragment of XPath extended with fixpoint operators. Using two-way alternating automata, we show that this language does combine desired expressiveness and computational properties, placing it as an attractive candidate for the definite node-selection query language for trees.