Piero A. Bonatti

A new semantics for overriding in description logics

Abstract Many modern applications of description logics (DLs, for short), such as biomedical ontologies and semantic web policies, provide fresh motivations for extending DLs with nonmonotonic inferences—a topic that has attracted a significant amount of attention along the years. Despite this, nonmonotonic inferences are not yet supported by DL technology due to a number of issues related to expressiveness, computational complexity, and optimizations. This paper contributes to the practical support of nonmonotonic inferences in description logics by introducing a new semantics expressly designed to address knowledge engineering needs. This formalism has appealing expressiveness, enjoys nice computational properties, and constitutes an interesting solution to an ample class of application needs. The formalism is validated through extensive comparison with the other nonmonotonic DLs, and systematic scalability tests. The test case generator and its novel validation methodology constitute a further contribution of this paper.

ERBAC: event-driven RBAC

Context-aware access control systems should reactively adapt access control decisions to dynamic environmental conditions. In this paper we present an extension of the TRBAC model that allows the specification and enforcement of general reactive policies. Then we extend XACML to support the new model, and illustrate a prototype implementation of the PDP.

E-Auctions for Multi-Cloud Service Provisioning

The cloud computing paradigm requires solutions supporting customers in the selection of services that satisfy their functional and non-functional requirements. These solutions must i) support the dynamic, multi-cloud nature of service provisioning, ii) manage scenarios where no total preference relation over service properties is available, and iii) prevent providers from misrepresenting or overstating their properties. In this paper we put forward the idea of modeling multi-cloud provisioning scenarios as procurement e-auctions (where the auctioneer is the customer and the bidders are service providers). We introduce a service selection process based on matching and ranking algorithms, and an e-auction mechanism that addresses the above requirements, encouraging trustworthy bids and therefore improving the truthfulness on the e-auction outcome. Finally we describe the implementation of a prototype used to evaluate the performance of our approach with respect to traditional query-based engines.

Datalog for security, privacy and trust

Logic-based policy languages are appreciated because of their clean semantics and expressiveness. Datalog has been used for a long time as a foundation of many security models and policy languages. Recently, Description Logics (DLs for short) have been adopted as policy languages, too. In this paper we carry out a comparison of Datalog and Description Logics as policy languages, based both on expressiveness analysis and on an assessment of the current maturity of the two fields, expressly related to the representation and reasoning tasks involved in policy authoring, enforcement, and management. We shall argue that Datalog-based approaches are currently more powerful and mature than those based on pure DLs, although the ongoing research on the latter might change the picture in a near future. The potential of hybrid approaches will be briefly discussed.

A Confidentiality Model for Ontologies

We illustrate several novel attacks to the confidentiality of knowledge bases (KB). Then we introduce a new confidentiality model, sensitive enough to detect those attacks, and a method for constructing secure KB views. We identify safe approximations of the background knowledge exploited in the attacks; they can be used to reduce the complexity of constructing secure KB views.

Optimizing the Computation of Overriding

We introduce optimization techniques for reasoning in

Event-driven RBAC

\mathcal {DL}^\mathrm {N}

Decidability of Circumscribed Description Logics Revisited

---a recently introduced family of nonmonotonic description logics whose characterizing features appear well-suited to model the examples naturally arising in biomedical domains and semantic web access control policies. Such optimizations are validated experimentally on large KBs with more than 30K axioms. Speedups exceed 1 order of magnitude. For the first time, response times compatible with real-time reasoning are obtained with nonmonotonic KBs of this size.