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Description Logic Knowledge and Action Bases
, 2013
"... Description logic Knowledge and Action Bases (KAB) are a mechanism for providing both a semantically rich representation of the information on the domain of interest in terms of a description logic knowledge base and actions to change such information over time, possibly introducing new objects. We ..."
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Cited by 19 (9 self)
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Description logic Knowledge and Action Bases (KAB) are a mechanism for providing both a semantically rich representation of the information on the domain of interest in terms of a description logic knowledge base and actions to change such information over time, possibly introducing new objects. We resort to a variant of DLLite where the unique name assumption is not enforced and where equality between objects may be asserted and inferred. Actions are specified as sets of conditional effects, where conditions are based on epistemic queries over the knowledge base (TBox and ABox), and effects are expressed in terms of new ABoxes. In this setting, we address verification of temporal properties expressed in a variant of firstorder µcalculus with quantification across states. Notably, we show decidability of verification, under a suitable restriction inspired by the notion of weak acyclicity in data exchange.
Verification of AgentBased Artifact Systems
, 2014
"... Artifact systems are a novel paradigm for specifying and implementing business processes described in terms of interacting modules called artifacts. Artifacts consist of data and lifecycles, accounting respectively for the relational structure of the artifacts ’ states and their possible evolution ..."
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Cited by 10 (7 self)
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Artifact systems are a novel paradigm for specifying and implementing business processes described in terms of interacting modules called artifacts. Artifacts consist of data and lifecycles, accounting respectively for the relational structure of the artifacts ’ states and their possible evolutions over time. In this paper we put forward artifactcentric multiagent systems, a novel formalisation of artifact systems in the context of multiagent systems operating on them. Differently from the usual processbased models of services, we give a semantics that explicitly accounts for the data structures on which artifact systems are defined. We study the model checking problem for artifactcentric multiagent systems against specifications expressed in a quantified version of temporalepistemic logic expressing the knowledge of the agents in the exchange. We begin by noting that the problem is undecidable in general. We identify a noteworthy class of systems that admit bisimilar, finite abstractions. It follows that we can verify these systems by investigating their finite abstractions; we also show that the corresponding model checking problem is EXPSPACEcomplete. We then introduce artifactcentric programs, compact and declarative representations of the programs governing both the artifact system and the agents. We show that, while these in principle generate infinitestate systems, under natural conditions their verification problem can be solved on finite abstractions that can be effectively computed from the programs. We exemplify the theoretical results here pursued through a mainstream procurement scenario from the artifact systems literature.
B.: Verification of golog programs over description logic actions. LTCSReport 1308, Chair of Automata Theory
, 2013
"... Abstract. Highlevel action programming languages such as Golog have successfully been used to model the behavior of autonomous agents. In addition to a logicbased action formalism for describing the environment and the effects of basic actions, they enable the construction of complex actions using ..."
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Cited by 7 (4 self)
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Abstract. Highlevel action programming languages such as Golog have successfully been used to model the behavior of autonomous agents. In addition to a logicbased action formalism for describing the environment and the effects of basic actions, they enable the construction of complex actions using typical programming language constructs. To ensure that the execution of such complex actions leads to the desired behavior of the agent, one needs to specify the required properties in a formal way, and then verify that these requirements are met by any execution of the program. Due to the expressiveness of the action formalism underlying Golog (Situation Calculus), the verification problem for Golog programs is in general undecidable. Action formalisms based on Description Logic (DL) try to achieve decidability of inference problems such as the projection problem by restricting the expressiveness of the underlying base logic. However, until now these formalisms have not been used within Golog programs. In the present paper, we introduce a variant of Golog where basic actions are defined using such a DLbased formalism, and show that the verification problem for such programs is decidable. This improves on our previous work on verifying properties of infinite sequences of DL actions in that it considers (finite and infinite) sequences of DL actions that correspond to (terminating and nonterminating) runs of a Golog program rather than just infinite sequences accepted by a Büchi automaton abstracting the program. 1
StateBoundedness in DataAware Dynamic Systems
"... Verification of dynamic systems that manipulate data, stored in a database or ontology, has lately received increasing attention. A plethora of recent works has shown that verification of systems working over unboundedly many data is decidable even for very rich temporal properties, provided that t ..."
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Cited by 3 (1 self)
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Verification of dynamic systems that manipulate data, stored in a database or ontology, has lately received increasing attention. A plethora of recent works has shown that verification of systems working over unboundedly many data is decidable even for very rich temporal properties, provided that the system is statebounded. This condition requires the existence of an overall bound on the amount of data stored in each single state along the system evolution. In general, checking stateboundedness is undecidable. An open question is whether it is possible to isolate significant classes of dynamic systems for which stateboundedness is decidable. In this paper we provide a strong negative answer, by resorting to a novel connection with variants of Petri nets. In particular, we show undecidability for systems whose data component contains unary relations only, and whose action component queries and updates such relations in a very limited way. To contrast this result, we propose interesting relaxations of the sufficient conditions proposed in the concrete setting of DataCentric Dynamic Systems, building on recent results on chase termination for tuplegenerating dependencies. 1
Bounded Epistemic Situation Calculus Theories
"... We define the class of ebounded theories in the epistemic situation calculus, where the number of fluent atoms that the agent thinks may be true is bounded by a constant. Such theories can still have an infinite domain and an infinite set of states. We show that for them verification of an expressi ..."
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Cited by 2 (2 self)
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We define the class of ebounded theories in the epistemic situation calculus, where the number of fluent atoms that the agent thinks may be true is bounded by a constant. Such theories can still have an infinite domain and an infinite set of states. We show that for them verification of an expressive class of firstorder µcalculus temporal epistemic properties is decidable. We also show that if the agent’s knowledge in the initial situation is ebounded and the objective part of an action theory maintains boundedness, then the entire epistemic theory is ebounded.
Shape and Content Incorporating Domain Knowledge into Shape Analysis
"... Abstract. The verification community has studied dynamic data structures primarily in a bottomup way by analyzing pointers and the shapes induced by them. Recent work in fields such as separation logic has made significant progress in extracting shapes from program source code. Many real world pro ..."
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Abstract. The verification community has studied dynamic data structures primarily in a bottomup way by analyzing pointers and the shapes induced by them. Recent work in fields such as separation logic has made significant progress in extracting shapes from program source code. Many real world programs however manipulate complex data whose structure and content is most naturally described by formalisms from object oriented programming and databases. In this paper, we attempt to bridge the conceptual gap between these two communities. Our approach is based on description logic, a widely used knowledge representation paradigm which gives a logical underpinning for diverse modeling frameworks such as UML and ER. We show how description logic can be used on top of an existing shape analysis to add content descriptions to the shapes. Technically, we assume that we have separation logic shape invariants obtained from a shape analysis tool, and requirements on the program data in terms of description logic. Thus, we obtain a modular description logic based verification methodology which is able to exploit shape information. 1
Model Checking Auctions as Artifact Systems: Decidability via Finite Abstraction
"... Abstract. The formal verification of auctions has recently received considerable attention in the AI and logic community. We tackle this problem by adopting methodologies and techniques originally developed for Artifact Systems, a novel paradigm in Service Oriented Computing. Specifically, we intro ..."
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Cited by 1 (0 self)
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Abstract. The formal verification of auctions has recently received considerable attention in the AI and logic community. We tackle this problem by adopting methodologies and techniques originally developed for Artifact Systems, a novel paradigm in Service Oriented Computing. Specifically, we introduce a typed version of artifactcentric multiagent systems (ACMAS), a multiagent setting for Artifact Systems, and consider the model checking problem against typed firstorder temporal epistemic specifications. Notably, this formal framework is expressive enough to capture a relevant class of auctions: parallel English (ascending bid) auctions. We prove decidability of the model checking problem for ACMAS via finite abstraction. In particular, we put forward a methodology to formally verify interesting properties of auctions. 1
On Decidable Verification of Nonterminating Golog Programs
"... The highlevel action programming language GOLOG has proven to be a useful means for the control of autonomous agents such as mobile robots. Usually, such agents perform openended tasks, and their control programs are hence nonterminating. Before deploying such a program to the robot, it is often ..."
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The highlevel action programming language GOLOG has proven to be a useful means for the control of autonomous agents such as mobile robots. Usually, such agents perform openended tasks, and their control programs are hence nonterminating. Before deploying such a program to the robot, it is often desirable if not crucial to verify that it meets certain requirements, preferably by means of an automated method. For this purpose, Claßen and Lakemeyer recently introduced algorithms for the verification of temporal properties of nonterminating GOLOG programs, based on the firstorder modal Situation Calculus variant ES, and regressionbased reasoning. However, while GOLOG’s high expressiveness is a desirable feature, it also means that their verification procedures cannot be guaranteed to terminate in general. In this paper, we address this problem by showing that, for a relevant subset, the verification of nonterminating GOLOG programs is indeed decidable, which is achieved by means of three restrictions. First, we use the ES variant of a decidable twovariable fragment of the Situation Calculus that was introduced by Gu and Soutchanski. Second, we have to restrict the GOLOG program to contain ground action only. Finally, we consider special classes of successor state axioms, namely the contextfree ones and those that only admit local effects.
Progression and Verification of Situation Calculus Agents with Bounded Beliefs
 In Proc. of AAMAS’14
"... In this paper we investigate agents that have incomplete information and make decisions based on their beliefs, expressed as situation calculus bounded action theories. Such theories have an infinite object domain, but the number of objects that belong to fluents at each time point is bounded by ..."
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In this paper we investigate agents that have incomplete information and make decisions based on their beliefs, expressed as situation calculus bounded action theories. Such theories have an infinite object domain, but the number of objects that belong to fluents at each time point is bounded by a given constant. Recently it has been shown that verifying temporal properties over such theories is decidable. Here, we first show that we can actually check whether an arbitrary action theory maintains boundedness. Secondly, we examine progression. Progression can be thought of as capturing the notion of belief states resulting from actions in the situation calculus. In the general case, such belief states can be expressed only in secondorder logic. Here, we show that for bounded action theories, progression, and hence belief states, can always be represented in firstorder logic. Based on this result, we further prove decidability of temporal verification over online executions, i.e., those executions resulting from agents performing only actions that are feasible according to their beliefs. Categories and Subject Descriptors