Mario R. F. Benevides

Building Reliable Web Services Compositions

The recent evolution of internet technologies, mainly guided by the Extensible Markup Language (XML) and its related technologies, are extending the role of the World Wide Web from information interaction to service interaction. This next wave of the internet era is being driven by a concept named Web services. The Web services technology provides the underpinning to a new business opportunity, i.e., the possibility of providing value-added Web services. However, the building of value-added services on this new environment is not a trivial task. Due to the many singularities of the Web service environment, such as the inherent structural and behavioral heterogeneity of Web services, as well as their strict autonomy, it is not possible to rely on the current models and solutions to build and coordinate compositions of Web services. In this paper, we present a framework for building reliable Web service compositions on top of heterogeneous and autonomous Web services.

Mediating heterogeneous Web services

Web services technology provides the foundation for a new business opportunity, i.e., the possibility of providing value-added Web services. However, building value-added services in this new environment is not a trivial task. Due to many singularities of the Web service environment, such as the inherent structural and behavioral heterogeneity of Web services, in addition to their strict autonomy, it is not possible to rely on current models and solutions to build and coordinate compositions of Web services. We present a mediation service layer within an architecture, named WebTransact, which provides the necessary mechanisms for homogenizing heterogeneous Web services. Such architecture separates the task of aggregating and homogenizing heterogeneous Web services from the task of specifying transaction interaction patterns, thus providing a new general mechanism to deal with the complexity introduced by a large number of Web services.

A Propositional Dynamic Logic for CCS Programs

This work presents a Propositional Dynamic Logic in which the programs are CCS terms (CCS-PDL). Its goal is to reason about properties of concurrent systems specified in CCS. CCS is a process algebra that models the concurrency and interaction between processes through individual acts of communication. At a first step, we consider only CCS processes without constants and give a complete axiomatization for this logic, which is very similar to *-free PDL. Then, we proceed to include CCS processes with constants. In this case, we impose some restrictions on the form of the recursive equations that can be built with those constants. We also give an axiomatization for this second logic and prove its completeness using a Fischer-Ladner construction. Unlike Concurrent PDL (with channels) [1,2], our logic has a simple Kripke semantics, a complete axiomatization and the finite model property.

Verification of epistemic properties in probabilistic multi-agent systems

Over the past decade Multi-Agent Systems (MAS) have emerged as a successful approach to develop distributed applications. In recent years proposals have been made to extend MAS models with probabilistic behavior. Languages to reason about such systems were presented in order to deal with uncertainty that can be encountered in practical application domains.While in recent works model checking techniques have been successfully applied for verifying knowledge in classical MAS, no methods for verifying knowledge in probabilistic MAS yet exist. This paper proposes such a model checking approach for probabilistic MAS. The approach comprises a compositional modeling process, a modal logic with operators for the specification of epistemic and temporal properties, the corresponding model checking procedure, and an outline of how these techniques can be implemented into existing model checking tools. The advantages of the chosen design include the possibility to analyze the MAS both from the global perspective as well as from the perspective of the agents, and the polynomial complexity of the model checking algorithm.

Propositional Dynamic Logic with Storing, Recovering and Parallel Composition

This work extends Propositional Dynamic Logic (PDL) with parallel composition operator and four atomic programs which formalize the storing and recovering of elements in data structures. A generalization of Kripke semantics is proposed that instead of using set of possible states it uses structured sets of possible states. This new semantics allows for representing data structures and using the five new operator one is capable of reasoning about the manipulation of these data structures. The use of the new language (PRSPDL) is illustrated with some examples. We present sound and complete set of axiom schemata and inference rules to prove all the valid formulas for a restricted fragment called RSPDLo.

Propositional dynamic logic for Petri nets

Propositional Dynamic Logic (PDL) is a multi-modal logic used for specifying and reasoning on sequential programs. Petri Net is a widely used formalism to specify and to analyse concurrent programs with a very nice graphical representation. In this work, we propose a PDL to reasoning about Petri Nets. First we define a compositional encoding of Petri Nets from basic nets as terms. Second, we use these terms as PDL programs and provide a compositional semantics to PDL Formulas. Finally, we present an axiomatization and prove completeness w.r.t. our semantics. The advantage of our approach is that we can do reasoning about Petri Nets using our dynamic logic and we do not need to to translate it to other formalisms. Moreover our approach is compositional allowing for construction of complex nets using basic ones.

Using modal logics to express and check global graph properties

Graphs are among the most frequently used structures in Computer Science. Some of the properties that must be checked in many applications are connectivity, acyclicity and the Eulerian and Hamiltonian properties. In this work, we analyze how we can express these four properties with modal logics. This involves two issues: whether each of the modal languages under consideration has enough expressive power to describe these properties and how complex (computationally) it is to use these logics to actually test whether a given graph has some desired property. First, we show that these properties are not definable in a basic modal logic or in any bisimulation-invariant extension of it, like the modal μ-calculus. We then show that it is possible to express some of the above properties in a basic hybrid logic. Unfortunately, the Hamiltonian and Eulerian properties still cannot be efficiently checked. In a second attempt, we propose an extension of CTL∗ with nominals and show that the Hamiltonian property can be more efficiently checked in this logic than in the previous one. In a third attempt, we extend the basic hybrid logic with the ↓ operator and show that we can check the Hamiltonian property with optimal (NP) complexity in this logic. Finally, we tackle the Eulerian property in two different ways. First, we develop a generic method to express edge-related properties in hybrid logics and use it to express the Eulerian property. Second, we express a necessary and sufficient condition for the Eulerian property to hold using a graded modal logic.

A Propositional Dynamic Logic for Concurrent Programs Based on the π-Calculus

This work presents a Propositional Dynamic Logic (@pDL) in which the programs are described in a language based on the @p-Calculus without replication. Our goal is to build a dynamic logic that is suitable for the description and verification of properties of communicating concurrent systems, in a similar way as PDL is used for the sequential case. We build a simple Kripke semantics for this logic, provide a complete axiomatization for it and show that it has the finite model property.

Modal logics for finite graphs

We present modal logics for four classes of finite graphs: finite directed graphs, finite acyclic directed graphs, finite undirected graphs and finite loopless undirected graphs. For all these modal proof theories we discuss soundness and completeness results with respect to each of these classes of graphs. Moreover, we investigate whether some well-known properties of undirected graphs are modally definable or not: k-colouring, planarity, connectivity and properties that a graph is Eulerian or Hamiltonian. Finally, we present an axiomatization for colouring and prove that it is sound and complete with respect to the class of finite k-colourable graphs. One of most interesting feature of this approach is the use of the axioms of Dynamic Logic together with the Lob axiom to ensure acyclicity.

On Graph Calculi for Multi-modal Logics

We introduce a method, based on graphical representation, for formulating sound and complete calculi for multi-modal logics. This approach provides uniform tools for expressing and manipulating modal formulas. We illustrate the method by constructing, in a natural manner, correct graph calculi for some multi-modal logics, which may include the global and difference modalities, and may have some special properties.