Fernando Luís Dotti

Verification of Distributed Object-Based Systems

Distributed systems for open environments, like the Internet, are becoming more frequent and important. However, it is difficult to assure that such systems have the required functional properties. In this paper we use a visual formal specification language, called Object-Based Graph Grammars (OBGG), to specify asynchronous distributed systems. After discussing the main concepts of OBGG, we propose an approach for the verification of OBGG specifications using model checking. This approach consists on the translation of OBGG specifications into PROMELA (PROcess/PROtocol MEta LAnguage), which is the input language of the SPIN model checker. The approach we use for verification allows one to write properties based on the OBGG specification instead of on the generated PROMELA model.

Translating Java Code to Graph Transformation Systems

We propose a faithful encoding of Java programs (written in a suitable fragment of the language) to Graph Transformation Systems. Every program is translated to a set of rules including some basic rules, common to all programs and providing the operational semantics of Java (data and control) operators, and the program specific rules, namely one rule for each method or constructor declared in the program.

Specification of mobile code system using graph grammars

In this paper we introduce a formal approach for the specification of mobile code systems. This approach is based on graph grammars, that is a formal description technique that is suitable for the description of highly parallel systems, and is intuitive even for non-theoreticians We define a special class of graph grammars using the concepts of object-based systems and include location information explicitly. Aspects of modularity and execution in an open environment are discussed.

Verifying Object-Based Graph Grammars

Object-Based Graph Grammars (OBGG) is a formal language suitable for the specification of distributed systems. On previous work, a translation from OBGG models to PROMELA (the input language of the SPIN model checker) was defined, enabling the verification of OBGG models using SPIN. This paper builds on these results, where we extend the approach for property specification and define an approach to interpret PROMELA traces as OBGG derivations, generating graphical counter-examples for properties that are not true for an OBGG model.

Verifying Object-based Graph Grammars

The development of concurrent and reactive systems is gaining importance since they are well-suited to modern computing platforms, such as the Internet. However, the development of correct concurrent and reactive systems is a non-trivial task. Object-based graph grammar (OBGG) is a visual formal language suitable for the specification of this class of systems. In previous work, a translation from OBGG to PROMELA (the input language of the SPIN model checker) was defined, enabling the verification of OBGG models using SPIN. In this paper we extend this approach in two different ways: (1) the approach for property specification is improved, enabling to prove properties not only about possible OBGG derivations, but also about the internal state of involved objects; (2) an approach is defined to interpret PROMELA races as OBGG derivations, generating graphical counter-examples for properties that are not true for a given OBGG model. Another contribution of this paper is (3) the definition of a method for model checking partial systems (isolated objects or a set of objects) using an assume-guarantee approach. A gas station system modeled with OBGGs is used to illustrate the contributions.

Analytical modeling of random waypoint mobility patterns

Mobility, in its various forms, is one of the sources of several technical challenges being addressed in the last years to achieve a more flexible computing and communication infrastructure. In this context, the study and characterization of node mobility in wireless networks is extremely important to foresee the node distribution in the network, thus enabling the creation of suitable models and a more accurate prediction of performance and dependability levels.In this paper we adopt a Markovian formalism, namely SAN (Stochastic Automata Networks), to model and analyze various aspects of the Random Waypoint mobility pattern. We first show the compatibility of our results with existing continuous state studies and then we extend the analysis of the Random Waypoint by addressing different specific, but far from irrelevant, aspects of the mobility pattern. In this sense, this contribution shows both results for this mobility pattern as well as the suitability of the SAN formalism to detailed description of such pattern

An Environment for the Development of Concurrent Object-Based Applications

Object-Based Graph Grammars (OBGG) is a formal specification language suitable for modeling concurrent object-based systems. On previous work we have mainly discussed the language along with case studies and analysis techniques (model checking and simulation) for systems described in OBGG. In this paper we present the set of tools we have developed and/or integrated to build an environment for the development of concurrent object-based systems. With this environment, we support the specification and analysis of concurrent object-based systems specified using OBGG.

Towards Theorem Proving Graph Grammars using Event-B

Graph grammars may be used as specification technique for different kinds of systems, specially in situations in which states are complex structures that can be adequately modeled as graphs (possibly with an attribute data part) and in which the behavior involves a large amount of parallelism and can be described as reactions to stimuli that can be observed in the state of the system. The verification of properties of such systems is a difficult task due to many aspects: in many situations the systems have an infinite number of states; states themselves are complex and large; there are a number of different computation possibilities due to the fact that rule applications may occur in parallel. There are already some approaches to verification of graph grammars based on model checking, but in these cases only finite state systems can be analyzed. Other approaches propose over- and/or under-approximations of the state-space, but in this case it is not possible to check arbitrary properties. In this work, we propose to use the Event-B formal method and its theorem proving tools to analyze graph grammars. We show that a graph grammar can be translated into an Event-B specification preserving its semantics, such that one can use several theorem provers available for Event-B to analyze the reachable states of the original graph grammar. The translation is based on a relational definition of graph grammars, that was shown to be equivalent to the Single-Pushout approach to graph grammars.

A formal framework for the development of concurrent object-based systems

In this paper we present a framework for developing concurrent object-based systems. The framework is based on graph grammars and includes techniques for specification, simulation, animation and verification.

Structured Markovian models for discrete spatial mobile node distribution

The study and characterization of node mobility in wireless networks is extremely important to foresee the node distribution in the network, enabling the creation of suitable models, and thus a more accurate prediction of performance and dependability levels.In this paper we adopt a structured Markovian formalism, namely SAN (Stochastic Automata Networks), to model and analyze two popular mobility models for wireless networks: the Random Waypoint and Random Direction.Our modeling considers mobility over a discrete space, i.e., over a space divided in a given number of slots, allowing a suitable analytical representation of structured regions. We represent several important aspects of mobility models, such as varying speed and pause times, and several border behaviors that may take place. One, two, and three-dimensional models are presented. For the two-dimensional models, we show that any regular or irregular convex polygon can be modeled, and we describe several routing strategies in two dimensions.In all cases, the spatial node distribution obtained from the steady state analysis is presented and whenever analogous results over continuous spaces were available in the literature, the comparison with the ones obtained in this paper is shown to be coherent.Besides showing the suitability of SAN to model this kind of reality, the paper also contributes to new findings for the modeled mobility models over a noncontinuous space.