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	Author	Chierichetti, Flavio; Lattanzi, Silvio; Mari, Federico; Panconesi, Alessandro
	Title	On Placing Skips Optimally in Expectation			Type	Conference Article
	Year	2008	Publication	Web Search and Web Data Mining (WSDM 2008)	Abbreviated Journal
	Volume		Issue		Pages	15-24
	Keywords	Information Retrieval
	Abstract	We study the problem of optimal skip placement in an inverted list. Assuming the query distribution to be known in advance, we formally prove that an optimal skip placement can be computed quite efficiently. Our best algorithm runs in time O(n log n), n being the length of the list. The placement is optimal in the sense that it minimizes the expected time to process a query. Our theoretical results are matched by experiments with a real corpus, showing that substantial savings can be obtained with respect to the tra- ditional skip placement strategy, that of placing consecutive skips, each spanning sqrt(n) many locations.
	Address
	Corporate Author				Thesis
	Publisher	Acm	Place of Publication		Editor	Najork, M.; Broder, A.Z.; Chakrabarti, S.
	Language		Summary Language		Original Title
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN		ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	yes
	Call Number	Sapienza @ mari @ ChiLatMar08			Serial	94
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	Author	Tronci, Enrico; Della Penna, Giuseppe; Intrigila, Benedetto; Venturini Zilli, Marisa
	Title	A Probabilistic Approach to Automatic Verification of Concurrent Systems			Type	Conference Article
	Year	2001	Publication	8th Asia-Pacific Software Engineering Conference (APSEC)	Abbreviated Journal
	Volume		Issue		Pages	317-324
	Keywords
	Abstract	The main barrier to automatic verification of concurrent systems is the huge amount of memory required to complete the verification task (state explosion). In this paper we present a probabilistic algorithm for automatic verification via model checking. Our algorithm trades space with time. In particular, when memory is full because of state explosion our algorithm does not give up verification. Instead it just proceeds at a lower speed and its results will only hold with some arbitrarily small error probability. Our preliminary experimental results show that by using our probabilistic algorithm we can typically save more than 30% of RAM with an average time penalty of about 100% w.r.t. a deterministic state space exploration with enough memory to complete the verification task. This is better than giving up the verification task because of lack of memory.
	Address
	Corporate Author				Thesis
	Publisher	IEEE Computer Society	Place of Publication	Macau, China	Editor
	Language		Summary Language		Original Title
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0-7695-1408-1	ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	yes
	Call Number	Sapienza @ mari @ apsec01			Serial	43
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	Author	Coppo, Mario; Dezani-Ciancaglini, Mariangiola; Giovannetti, Elio; Salvo, Ivano
	Title	Mobility Types for Mobile Processes in Mobile Ambients			Type	Journal Article
	Year	2003	Publication	Electr. Notes Theor. Comput. Sci.	Abbreviated Journal
	Volume	78	Issue		Pages
	Keywords
	Abstract	We present an ambient-like calculus in which the open capability is dropped, and a new form of Ã¢â‚¬Å“lightweightÃ¢â‚¬Â process mobility is introduced. The calculus comes equipped with a type system that allows the kind of values exchanged in communications and the access and mobility properties of processes to be controlled. A type inference procedure determines the Ã¢â‚¬Å“minimalÃ¢â‚¬Â requirements to accept a system or a component as well typed. This gives a kind of principal typing. As an expressiveness test, we show that some well known calculi of concurrency and mobility can be encoded in our calculus in a natural way.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Summary Language		Original Title
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN		ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	yes
	Call Number	Sapienza @ mari @ Coppo-Dezani-Giovannetti-Salvo:03			Serial	74
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	Author	Barbanera, Franco; Dezani-Ciancaglini, Mariangiola; Salvo, Ivano; Sassone, Vladimiro
	Title	A Type Inference Algorithm for Secure Ambients			Type	Journal Article
	Year	2002	Publication	Electronic Notes in Theoretical Computer Science	Abbreviated Journal
	Volume	62	Issue		Pages	83-101
	Keywords
	Abstract	We consider a type discipline for the Ambient Calculus that associates ambients with security levels and constrains them to be traversed by or opened in ambients of higher security clearance only. We present a bottom-up algorithm that, given an untyped process P, computes a minimal set of constraints on security levels such that all actions during runs of P are performed without violating the security level priorities. Such an algorithm appears to be a prerequisite to use type systems to ensure security properties in the web scenario.
	Address
	Corporate Author				Thesis
	Publisher	Elsevier	Place of Publication		Editor
	Language		Summary Language		Original Title
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN		ISBN		Medium
	Area		Expedition		Conference
	Notes	TOSCA 2001, Theory of Concurrency, Higher Order Languages and Types			Approved	yes
	Call Number	Sapienza @ mari @ Barbanera-Dezani-Salvo-Sassone:01			Serial	73
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	Author	Della Penna, Giuseppe; Intrigila, Benedetto; Melatti, Igor; Tronci, Enrico; Venturini Zilli, Marisa
	Title	Finite horizon analysis of Markov Chains with the Mur$\varphi$ verifier			Type	Journal Article
	Year	2006	Publication	Int. J. Softw. Tools Technol. Transf.	Abbreviated Journal
	Volume	8	Issue	4	Pages	397-409
	Keywords
	Abstract	In this paper we present an explicit disk-based verification algorithm for Probabilistic Systems defining discrete time/finite state Markov Chains. Given a Markov Chain and an integer k (horizon), our algorithm checks whether the probability of reaching an error state in at most k steps is below a given threshold. We present an implementation of our algorithm within a suitable extension of the Mur$\varphi$ verifier. We call the resulting probabilistic model checker FHP-Mur$\varphi$ (Finite Horizon Probabilistic Mur$\varphi$). We present experimental results comparing FHP-Mur$\varphi$ with (a finite horizon subset of) PRISM, a state-of-the-art symbolic model checker for Markov Chains. Our experimental results show that FHP-Mur$\varphi$ can handle systems that are out of reach for PRISM, namely those involving arithmetic operations on the state variables (e.g. hybrid systems).
	Address
	Corporate Author				Thesis
	Publisher	Springer-Verlag	Place of Publication	Berlin, Heidelberg	Editor
	Language		Summary Language		Original Title
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1433-2779	ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	yes
	Call Number	Sapienza @ mari @ Dimtz06			Serial	78
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	Author	Della Penna, Giuseppe; Intrigila, Benedetto; Melatti, Igor; Tronci, Enrico; Venturini Zilli, Marisa
	Title	Exploiting Transition Locality in Automatic Verification of Finite State Concurrent Systems			Type	Journal Article
	Year	2004	Publication	Sttt	Abbreviated Journal
	Volume	6	Issue	4	Pages	320-341
	Keywords
	Abstract	In this paper we show that statistical properties of the transition graph of a system to be verified can be exploited to improve memory or time performances of verification algorithms. We show experimentally that protocols exhibit transition locality. That is, with respect to levels of a breadth-first state space exploration, state transitions tend to be between states belonging to close levels of the transition graph. We support our claim by measuring transition locality for the set of protocols included in the Mur$\varphi$ verifier distribution. We present a cache-based verification algorithm that exploits transition locality to decrease memory usage and a disk-based verification algorithm that exploits transition locality to decrease disk read accesses, thus reducing the time overhead due to disk usage. Both algorithms have been implemented within the Mur$\varphi$ verifier. Our experimental results show that our cache-based algorithm can typically save more than 40% of memory with an average time penalty of about 50% when using (Mur$\varphi$) bit compression and 100% when using bit compression and hash compaction, whereas our disk-based verification algorithm is typically more than ten times faster than a previously proposed disk-based verification algorithm and, even when using 10% of the memory needed to complete verification, it is only between 40 and 530% (300% on average) slower than (RAM) Mur$\varphi$ with enough memory to complete the verification task at hand. Using just 300 MB of memory our disk-based Mur$\varphi$ was able to complete verification of a protocol with about $10^9$ reachable states. This would require more than 5 GB of memory using standard Mur$\varphi$.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Summary Language		Original Title
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN		ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	yes
	Call Number	Sapienza @ mari @ DIMTZ04j			Serial	91
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	Author	Mari, Federico; Tronci, Enrico
	Title	CEGAR Based Bounded Model Checking of Discrete Time Hybrid Systems			Type	Conference Article
	Year	2007	Publication	Hybrid Systems: Computation and Control (HSCC 2007)	Abbreviated Journal
	Volume		Issue		Pages	399-412
	Keywords	Model Checking, Abstraction, CEGAR, SAT, Hybrid Systems, DTHS
	Abstract	Many hybrid systems can be conveniently modeled as Piecewise Affine Discrete Time Hybrid Systems PA-DTHS. As well known Bounded Model Checking (BMC) for such systems comes down to solve a Mixed Integer Linear Programming (MILP) feasibility problem. We present a SAT based BMC algorithm for automatic verification of PA-DTHSs. Using Counterexample Guided Abstraction Refinement (CEGAR) our algorithm gradually transforms a PA-DTHS verification problem into larger and larger SAT problems. Our experimental results show that our approach can handle PA-DTHSs that are more then 50 times larger than those that can be handled using a MILP solver.
	Address
	Corporate Author				Thesis
	Publisher	Springer	Place of Publication		Editor	Bemporad, A.; Bicchi, A.; Buttazzo, G.C.
	Language		Summary Language		Original Title
	Series Editor		Series Title	Lecture Notes in Computer Science	Abbreviated Series Title
	Series Volume	4416	Series Issue		Edition
	ISSN		ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	yes
	Call Number	Sapienza @ mari @ MarTro07			Serial	92
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	Author	Della Penna, Giuseppe; Intrigila, Benedetto; Melatti, Igor; Tronci, Enrico; Venturini Zilli, Marisa
	Title	Finite Horizon Analysis of Stochastic Systems with the Mur$\varphi$ Verifier			Type	Conference Article
	Year	2003	Publication	Theoretical Computer Science, 8th Italian Conference, ICTCS 2003, Bertinoro, Italy, October 13-15, 2003, Proceedings	Abbreviated Journal
	Volume		Issue		Pages	58-71
	Keywords
	Abstract	Many reactive systems are actually Stochastic Processes. Automatic analysis of such systems is usually very difficult thus typically one simplifies the analysis task by using simulation or by working on a simplified model (e.g. a Markov Chain). We present a Finite Horizon Probabilistic Model Checking approach which essentially can handle the same class of stochastic processes of a typical simulator. This yields easy modeling of the system to be analyzed together with formal verification capabilities. Our approach is based on a suitable disk based extension of the Mur$\varphi$ verifier. Moreover we present experimental results showing effectiveness of our approach.
	Address
	Corporate Author				Thesis
	Publisher	Springer	Place of Publication		Editor	Blundo, C.; Laneve, C.
	Language		Summary Language		Original Title
	Series Editor		Series Title	Lecture Notes in Computer Science	Abbreviated Series Title
	Series Volume	2841	Series Issue		Edition
	ISSN	3-540-20216-1	ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	yes
	Call Number	Sapienza @ mari @ DIMTZ03c			Serial	90
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	Author	Della Penna, Giuseppe; Intrigila, Benedetto; Melatti, Igor; Tronci, Enrico; Venturini Zilli, Marisa
	Title	Bounded Probabilistic Model Checking with the Mur$\varphi$ Verifier			Type	Conference Article
	Year	2004	Publication	Formal Methods in Computer-Aided Design, 5th International Conference, FMCAD 2004, Austin, Texas, USA, November 15-17, 2004, Proceedings	Abbreviated Journal
	Volume		Issue		Pages	214-229
	Keywords
	Abstract	In this paper we present an explicit verification algorithm for Probabilistic Systems defining discrete time/finite state Markov Chains. We restrict ourselves to verification of Bounded PCTL formulas (BPCTL), that is, PCTL formulas in which all Until operators are bounded, possibly with different bounds. This means that we consider only paths (system runs) of bounded length. Given a Markov Chain $\cal M$ and a BPCTL formula Φ, our algorithm checks if Φ is satisfied in $\cal M$. This allows to verify important properties, such as reliability in Discrete Time Hybrid Systems. We present an implementation of our algorithm within a suitable extension of the Mur$\varphi$ verifier. We call FHP-Mur$\varphi$ (Finite Horizon Probabilistic Mur$\varphi$) such extension of the Mur$\varphi$ verifier. We give experimental results comparing FHP-Mur$\varphi$ with (a finite horizon subset of) PRISM, a state-of-the-art symbolic model checker for Markov Chains. Our experimental results show that FHP-Mur$\varphi$ can effectively handle verification of BPCTL formulas for systems that are out of reach for PRISM, namely those involving arithmetic operations on the state variables (e.g. hybrid systems).
	Address
	Corporate Author				Thesis
	Publisher	Springer	Place of Publication		Editor	Hu, A.J.; Martin, A.K.
	Language		Summary Language		Original Title
	Series Editor		Series Title	Lecture Notes in Computer Science	Abbreviated Series Title
	Series Volume	3312	Series Issue		Edition
	ISSN	3-540-23738-0	ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	yes
	Call Number	Sapienza @ mari @ Dimtz04			Serial	87
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	Author	Tronci, Enrico; Della Penna, Giuseppe; Intrigila, Benedetto; Venturini Zilli, Marisa
	Title	Exploiting Transition Locality in Automatic Verification			Type	Conference Article
	Year	2001	Publication	11th IFIP WG 10.5 Advanced Research Working Conference on Correct Hardware Design and Verification Methods (CHARME)	Abbreviated Journal
	Volume		Issue		Pages	259-274
	Keywords
	Abstract	In this paper we present an algorithm to contrast state explosion when using Explicit State Space Exploration to verify protocols. We show experimentally that protocols exhibit transition locality. We present a verification algorithm that exploits transition locality as well as an implementation of it within the Mur$\varphi$ verifier. Our algorithm is compatible with all Breadth First (BF) optimization techniques present in the Mur$\varphi$ verifier and it is by no means a substitute for any of them. In fact, since our algorithm trades space with time, it is typically most useful when one runs out of memory and has already used all other state reduction techniques present in the Mur$\varphi$ verifier. Our experimental results show that using our approach we can typically save more than 40% of RAM with an average time penalty of about 50% when using (Mur$\varphi$) bit compression and 100% when using bit compression and hash compaction.
	Address
	Corporate Author				Thesis
	Publisher	Springer	Place of Publication	Livingston, Scotland, UK	Editor	Margaria, T.; Melham, T.F.
	Language		Summary Language		Original Title
	Series Editor		Series Title	Lecture Notes in Computer Science	Abbreviated Series Title
	Series Volume	2144	Series Issue		Edition
	ISSN	3-540-42541-1	ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	yes
	Call Number	Sapienza @ mari @ charme01			Serial	44
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