43271530
Compositional analysis for verification of parameterized systems
Many safety-critical systems that have been considered by the verification community are parameterized by the number of concurrent components in the system, and hence describe an infinite family of systems. Traditional model checking techniques can only be used to verify specific instances of this family. In this paper, we present a technique based on compositional model checking and program analysis for automatic verification of infinite families of systems. The technique views a parameterized system as an expression in a process algebra (CCS) and interprets this expression over a domain of formulas (modal mu-calculus), considering a process as a property transformer. The transformers are constructed using partial model checking techniques. At its core, our technique solves the verification problem by finding the limit of a chain of formulas. We present a widening operation to find such a limit for properties expressible in a subset of modal mu-calculus. We describe the verification of a number of parameterized systems using our technique to demonstrate its utility.
16902988
A Cost-Sensitive Model for Preemptive Intrusion Response Systems
The proliferation of complex and fast-spreading intrusions not only requires advances in intrusion detection mechanisms but also demands development of sophisticated and automated intrusion response systems. In this paper we present a novel cost-sensitive model for intrusion response that incorporates preemptive deployment of the response actions. Specifically, our technique relies on comparing the cost of deploying a response against the cost of damage caused by an "'un-attended" intrusion and decides to preemptively deploy a response with maximum benefit. Our technique further allows adaptation of responses to the changing environment through evaluation of success and failure of previously triggered responses. We demonstrate the advantages of the approach and evaluate it using a damage reduction metric.
9852130
Parallel Web Service Composition in MoSCoE: A Choreography-Based Approach
We present a goal-driven approach to model a choreographer for realizing composite Web services. In this framework, the users start with an abstract, and possibly incomplete functional specification of a desired goal service. This specification is used to compose a choreographer that allows communication between the client and the set of available component services, and is functionally equivalent to the goal service. However, if such a composition cannot be realized, the proposed approach identifies the cause(s) for the failure of composition. This information can be used by the user to minimally reformulate the goal to reduce the `gap' between the desired functionality. The process can be iterated until a feasible composition is realized or the user decides to abort. The approach ensures that (i) a choreographer, if one is produced by our composition algorithm, in fact realizes the user-specified goal functionality; and (ii) the algorithm is guaranteed to find a composition that meets the user needs as captured in the goal specifications (whenever such a composition exists)
121785
Generation of All Counter-Examples for Push-Down Systems
We present a new, on-the-fly algorithm that given a push-down model representing a sequential program with (recursive) procedure calls and an extended finite-state automaton representing (the negation of) a safety property, produces a succinct, symbolic representation of all counter-examples; i.e., traces of system behaviors that violate the property. The class of what we call minimum-recursion loop-free counter-examples can then be generated from this representation on an as-needed basis and presented to the user. Our algorithm is also applicable, without modification, to finite-state system models. Simultaneous consideration of multiple counter-examples can minimize the number of model-checking runs needed to recognize common root causes of property violations. We illustrate the use of our techniques via application to a Java-Tar utility and an FTP-server program, and discuss a prototype tool implementation which offers several abstraction techniques for easy-viewing of generated counter-examples.
43133187
Parameterized Verification of pi-Calculus Systems
In this paper we present an automatic verification technique for parameterized systems where the subsystem behavior is modeled using the π-calculus. At its core, our technique treats each process instance in a system as a property transformer. Given a property ϕ that we want to verify of an N-process system, we use a partial model checker to infer the property ϕ′ (stated as a formula in a sufficiently rich logic) that must hold of an (N – 1)-process system. If the sequence of formulas ϕ,ϕ′,... thus constructed converges, and the limit is satisfied by the deadlocked process, we can conclude that the N-process system satisfies ϕ. To this end, we develop a partial model checker for the π-calculus that uses an expressive value-passing logic as the property language. We also develop a number of optimizations to make the model checker efficient enough for routine use, and a light-weight widening operator to accelerate convergence. We demonstrate the effectiveness of our technique by using it to verify properties of a wide variety of parameterized systems that are beyond the reach of existing techniques.
12323199
On Context-Specific Substitutability of Web Services
Web service substitution refers to the problem of identifying a service that can replace another service in the context of a composition with a specified functionality. Existing solutions to this problem rely on detecting the functional and behavioral equivalence of a particular service to be replaced and candidate services that could replace it. We introduce the notion of context-specific substitutability, where context refers to the overall functionality of the composition that is required to be maintained after replacement of its constituents. Using the context information, we investigate two variants of the substitution problem, namely environment-independent and environment- dependent, where environment refers to the constituents of a composition and show how the substitutability criteria can be relaxed within this model. We provide a logical formulation of the resulting criteria based on model checking techniques as well as prove the soundness and completeness of the proposed approach.
5085726
Uniform quantifier elimination and constraint query processing
Saugata Basu* Mathematical Sciences Research Institute Berkeley, CA 94720, USA
8225775
A global lower bound on parameter estimation error with periodic distortion functions
We present a global Ziv-Zakai (1969) type lower bound on the mean square error for estimation of signal parameter vectors, where some components of the distortion function may be periodic. Periodic distortion functions arise naturally in the context of direction of arrival or phase estimation problems. The bound is applied to an image registration problem, and compared to the performance of the maximum-likelihood estimator (MLE).
761465
New results on quantifier elimination over real closed fields and applications to constraint databases
In this paper, we give a new algorithm for quantifier elimination in the first order theory of real closed fields that improves the complexity of the best known algorithm for this problem till now. Unlike previously known algorithms [Basu et al. 1996; Renegar 1992; Heintz et al. 1990], the combinatorial part of the complexity (the part depending on the number of polynomials in the input) of this new algorithm is independent of the number of free variables. Moreover, under the assumption that each polynomial in the input depends only on a constant number of the free variables, the algebraic part of the complexity(the part depending on the degrees of the input polynomials) can also be made independent of the number of free variables. This new feature of our algorithm allow us to obtain a new algorithm for a variant of the quantifier elimination problem. We give an almost optimal algorithm for this new problem, which we call the uniform quantifier elimination problem.
Using tthe uniform quantifier elimination algorithm, we give an algorithm for solving a problem arising in the field of constraint databases with real polynomial constraints. We give an algorithm for converting a query with natural domain semantics to an equivalent one with active domain semantics. A nonconstructive version of this result was proved in Benedikt et al. [1998]. Very recently, a constructive proof was also given independently in Benedikt and Libkin [1997]. However, complexity issues were not considered and no algorithm with a reasonable complexity bound was known for this latter problem till now.
We also point out interesting logical consequences of this algorithmic result, concerning the expressive power of a constraint query language over the reals. This leads to simpler and constructive proofs for these inexpressibility results than the ones known before.
Moreover, our improved algorithm for performing quantifier elimination immediately leads to improved algorithms for several problems for which quantifier elimination is a basic step, for example, the problem of computing the closure of a given semi-algebraic set.
2261271
Selecting and Composing Web Services through Iterative Reformulation of Functional Specifications
We propose a specification-driven approach to Web service composition. The proposed framework allows users to start with a high-level, possibly incomplete specification of a desired (goal) service that is to be realized using a subset of the available component services. These services are represented by the system using transition systems augmented with guards over variables with infinite domains and are used to determine a strategy for their composition that would realize the goal service. In the event that the goal service cannot be realized using the available services, the system identifies the cause(s) for such failure which can then be used by the developer to reformulate the goal specification. Thus, the system supports Web service composition through iterative refinement of the functional specifications. We present a prototype implementation in tabled-logic programming environment that illustrates the key features of the proposed approach
6997851
Computing the betti numbers of arrangements
(MATH) In this paper, we consider the problem of computing the Betti numbers of an arrangement of $n$ compact semi-algebraic sets, $S_1,\ldots,S_n \subset \R^k$, where each $S_i$ is described using a constant number of polynomials with degrees bounded by a constant. Such arrangements are ubiquitous in computational geometry. We give an algorithm for computing $\ell$-th Betti number, $\beta_\ell(\cup_i S_i), 0 \leq \ell \leq k-1$, using $O(n^{\ell+2})$ algebraic operations. Additionally, one has to perform linear algebra on matrices of size bounded by $O(n^{\ell+1})$. All previous algorithms for computing the Betti numbers of arrangements, triangulated the arrangement giving rise to a complex of size $O(n^{2^k})$ in the worst case. To our knowledge this is the first algorithm for computing $\beta_\ell(\cup_i S_i)$ that does not rely on such a global triangulation, and has a graded complexity which depends on $\ell$.