Marco Alberti

A spatial agent-based model for assessing strategies of adaptation to climate and tourism demand changes in an alpine tourism destination

A vast body of literature suggests that the European Alpine Region is amongst the most sensitive socio-ecosystems to climate change impacts. Our model represents the winter tourism socio-ecosystem of Auronzo di Cadore, located in the Dolomites (Italy), which economic and environmental conditions are highly vulnerable to climate variations. This agent-based model includes eight types of agents corresponding to different winter tourist profiles based on their socio-economic background and activity targets. The model is calibrated with empirical data while results are authenticated through direct interaction of local stakeholders with the model. The model is then used for assessing three hypothetical and contrasted infrastructure-oriented adaptation strategies for the winter tourism industry, that have been previously discussed with local stakeholders, as possible alternatives to the business-as-usual situation. These strategies are tested against multiple future scenarios that include: (a) future weather conditions in terms of snow cover and temperature, (b) the future composition and total number of tourists and (c) the type of market competition. A set of socio-economic indicators, which are strongly coupled with relevant environmental consequences, are considered in order to draw conclusions on the robustness of the selected strategies.

Normative systems represented as hybrid knowledge bases

Normative systems have been advocated as an effective tool to regulate interaction in multi-agent systems. n nLogic programming rules intuitively correspond to conditional norms, and their semantics is based on the closed world assumption, which allows default negation, often used in norms. However, there are cases where the closed world assumption is clearly not adequate, and others that require reasoning about unknown individuals, which is not possible in logic programming. n nOn the other hand, description logics are based on the open world assumption and support reasoning about unknown individuals, but do not support default negation. n nIn this paper, we demonstrate the need for the aforementioned features (closed and open world assumptions, and reasoning about unknown individuals) in order to model human laws, with examples from the Portuguese Penal Code. We advocate the use of hybrid knowledge bases combining rules and ontologies, which provide the joint expressivity of logic programming and description logics. n nWe define a normative scenario as the pair of a set of facts and a set of norms, and give it a formal semantics by translation into an MKNF knowledge base. n nWe describe the implementation of the language, which computes the relevant consequences of given facts and norms, and use it to establish the resulting sentence in a penal scenario.

Abductive Logic Programming as an Effective Technology for the Static Verification of Declarative Business Processes

We discuss the static verification of declarative Business Processes. We identify four desiderata about verifiers, and propose a concrete framework which satisfies them. The framework is based on the ConDec graphical notation for modeling Business Processes, and on Abductive Logic Programming technology for verification of properties. Empirical evidence shows that our verification method seems to perform and scale better, in most cases, than other state of the art techniques (model checkers, in particular). A detailed study of our framework’s theoretical properties proves that our approach is sound and complete when applied to ConDec models that do not contain loops, and it is guaranteed to terminate when applied to models that contain loops.

The CHR-based Implementation of the SCIFF Abductive System

Abduction is a form of inference that supports hypothetical reasoning and has been applied to a number of domains, such as diagnosis, planning, protocol verification. Abductive Logic Programming ALP is the integration of abduction in logic programming. Usually, the operational semantics of an ALP language is defined as a proof procedure. The first implementations of ALP proof-procedures were based on the meta-interpretation technique, which is flexible but limits the use of the built-in predicates of logic programming systems. Another, more recent, approach exploits theoretical results on the similarity between abducibles and constraints. With this approach, which bears the advantage of an easy integration with built-in predicates and constraints, Constraint Handling Rules has been the language of choice for the implementation of abductive proof procedures. The first CHR-based implementation mapped integrity constraints directly to CHR rules, which is an efficient solution, but prevents defined predicates from being in the body of integrity constraints and does not allow a sound treatment of negation by default. In this paper, we describe the CHR-based implementation of the SCIFF abductive proof-procedure, which follows a different approach. The SCIFF implementation maps integrity constraints to CHR constraints, and the transitions of the proof-procedure to CHR rules, making it possible to treat default negation, while retaining the other advantages of CHR-based implementations of ALP proof-procedures.

NO Revision and NO Contraction

One goal of normative multi-agent system theory is to formulate principles for normative system change that maintain the rule-like structure of norms and preserve links between norms and individual agent obligations. A central question raised by this problem is whether there is a framework for norm change that is at once specific enough to capture this rule-like behavior of norms, yet general enough to support a full battery of norm and obligation change operators. In this paper we propose an answer to this question by developing a bimodal logic for norms and obligations called NO. A key to our approach is that norms are treated as propositional formulas, and we provide some independent reasons for adopting this stance. Then we define norm change operations for a wide class of modal systems, including the class of NO systems, by constructing a class of modal revision operators that satisfy all the AGM postulates for revision, and constructing a class of modal contraction operators that satisfy all the AGM postulates for contraction. More generally, our approach yields an easily extendable framework within which to work out principles for a theory of normative system change.

A Computational Logic Application Framework for Service Discovery and Contracting

In Semantic Web technologies, searching for a service means identifying components that can potentially satisfy user needs in terms of inputs and outputs discovery and devise a fruitful interaction with the customer contracting. In this paper, the authors present an application framework that encompasses both the discovery and the contracting steps in a unified search process. In particular, the authors accommodate service discovery by ontology-based reasoning and contracting by reasoning about behavioural interfaces, published in a formal language. To this purpose, the authors consider a formal approach grounded on Computational Logic. They define, illustrate, and evaluate a framework, called SCIFF Reasoning Engine SRE, which can establish if a Semantic Web Service and a requester can fruitfully inter-operate, by computing a possible interaction plan based on the behavioural interfaces of both. The same operational machinery used for contracting can be used for runtime verification.

Deon + : abduction and constraints for normative reasoning

Deontic concepts and operators have been widely used in several fields where representation of norms is needed, including legal reasoning and normative multi-agent systems. n nIn the meantime, abductive logic programming (ALP for short) has been exploited to formalize societies of agents, commitments and institutions, taking advantage from ALP operational support as (static or dynamic) verification tool. n nNonetheless, the modal nature of deontic operators smoothly fits into abductive semantics and abductive reasoning, where hypotheses can be raised at run-time on the basis of the specified formulas. n nIn recent works, a mapping of the most common deontic operators (obligation, prohibition, permission) to the abductive expectations of an ALP framework for agent societies has been proposed. This mapping was supported by showing a correspondence between declarative semantics of abductive expectations and Kripke semantics for deontic operators. n nBuilding upon such correspondence, in this work we introduce Deon +, a language where the two basic deontic operators (namely, obligation and prohibition) are enriched with quantification over time, by means of ALP and Constraint Logic Programming (CLP for short). In this way, we can take into account different flavors for obligations and prohibitions over time, i.e., existential or universal. We also discuss how to address consistency verification of such deontic specifications by a suitable ALP proof procedure, enriched with CLP constraints.

Integration of Abductive Reasoning and Constraint Optimization in SCIFF

Abductive Logic Programming (ALP) and Constraint Logic Programming (CLP) share the feature to constrain the set of possible solutions to a program via integrity or CLP constraints. These two frameworks have been merged in works by various authors, who developed efficient abductive proof-procedures empowered with constraint satisfaction techniques. However, while almost all CLP languages provide algorithms for finding an optimal solution with respect to some objective function (and not just any solution), the issue has received little attention in ALP. n nIn this paper we show how optimisation meta-predicates can be included in abductive proof-procedures, achieving in this way a significant improvement to research and practical applications of abductive reasoning. n nIn the paper, we give the declarative and operational semantics of an abductive proof-procedure that encloses constraint optimization meta-predicates, and we prove soundness in the three-valued completion semantics. In the proof-procedure, the abductive logic program can invoke optimisation meta-predicates, which can invoke abductive predicates, in a recursive way.

Observation strategies for event detection with incidence on runtime verification: theory, algorithms, experimentation

Many applications (such as system and user monitoring, runtime verification, diagnosis, observation-based decision making, intention recognition) all require to detect the occurrence of an event in a system, which entails the ability to observe the system. Observation can be costly, so it makes sense to try and reduce the number of observations, without losing full certainty about the event’s actual occurrence. In this paper, we propose a formalization of this problem. We formally show that, whenever the event to be detected follows a discrete spatial or temporal pattern, then it is possible to reduce the number of observations. We discuss exact and approximate algorithms to solve the problem, and provide an experimental evaluation of them. We apply the resulting algorithms to verification of linear temporal logics formulæ. Finally, we discuss possible generalizations and extensions, and, in particular, how event detection can benefit from logic programming techniques.