Gianni Conte

The effect of execution policies on the semantics and analysis of stochastic Petri nets

Petri nets in which random delays are associated with atomic transitions are defined in a comprehensive framework that contains most of the models already proposed in the literature. To include generally distributed firing times into the model one must specify the way in which the next transition to fire is chosen, and how the model keeps track of its past history; this set of specifications is called an execution policy. A discussion is presented of the impact that different execution policies have on semantics of the mode, as well as the characteristics of the stochastic process associated with each of these policies. When the execution policy is completely specified by the transition with the minimum delay (race policy) and the firing distributions are of the phase type, an algorithm is provided that automatically converts the stochastic process into a continuous time homogeneous Markov chain. An execution policy based on the choice of the next transition to fire independently of the associated delay (preselection policy) is introduced, and its semantics is discussed together with possible implementation strategies. >

Generalized stochastic Petri nets: a definition at the net level and its implications

The class of Petri nets obtained by eliminating timing from generalized stochastic Petri net (GSPN) models while preserving the qualitative behavior is identified. Structural results for those nets are derived, obtaining the first structural analysis of Petri nets with priority and inhibitor arcs. A revision of the GSPN definition based on the structural properties of the models is presented. It is shown that for a (wide) class of nets, the definition of firing probabilities of conflicting immediate transitions does not require the information on reachable markings. Identification of the class of models for which the net-level specification is possible is also based on the structural analysis results. The procedure for the model specification is illustrated by means of an example. It is also shown that a net-level specification of the model associated with efficient structural analysis techniques can have a substantial impact on model analysis. >

An introduction to generalized stochastic Petri nets

Abstract The paper decribes the GSPN approach to the performance evaluation of distributed systems. The structural properties and temporal specifications of GSPN are summarized, and application examples are then illustrated, trying to emphasize the methodology to be followed in the model development and validation, rather than the numerical results that can be obtained from the specific models developed in the paper.

Parallel State Space Exploration for GSPN Models

Generalized Stochastic Petri Nets (GSPN) have gained a wide acceptance as a modeling tool for the performance analysis of concurrent systems. However, the applicability of this methodology is severely limited by the potential state space explosion phenomenon. In this paper we describe massively parallel approaches to the most computing-intensive part of the solution of GSPN models: the state space construction. The effectiveness of these parallel approaches stays, for every GSPN, in their ability to deal with very large reachability spaces in reasonable time. Both the SIMD and the MIMD programming models are considered, and examples are given using recent massively parallel processing architectures (CM-5, T3D).

SP2A: a service-oriented framework for P2P-based Grids

Service-Oriented Architectures (SOAs) are rapidly becoming the key approach for achieving new levels of interoperability and scalability in the development of Grid applications. Within SOA solutions, current approaches for advertising service providers and for allowing prospective clients to discover them are mostly based on centralized registries. Envisioning Virtual Organizations in which all participants are both resource providers and consumers, in a peer-to-peer fashion, seems to be an appealing approach.In this paper we propose the Service-oriented Peer-to-Peer Architecture (SP2A), a framework enabling peer-to-peer resource sharing in Grid environments. Resources are not directly exposed but can be accessed through Resource Provision Services, whose semantically enriched interfaces are published in the network. The framework has been implemented as a Java API, which currently supports a number of important technologies such as JXTA (peer-to-peer routing), Web Services (service deployment), and OWL-S (semantic description of services).

The Paprica massively parallel processor

This paper describes a complete 6-year project, starting from its theoretical basis up to the hardware and software system implementation, and to the description of its future evolution. The main goal of the project is to develop a subsystem that operates as a processing unit attached to a standard workstation and in perspective as a low-cost low-sized specialized embedded system devoted to low level image analyses and cellular neural networks emulation. The architecture has been extensively used for basic low level image analysis tasks up to optical flow computation and feature tracking, showing encouraging performances even in the first prototype version.<<ETX>>

Analysis of large GSPN models: a distributed solution tool

Distributed computing systems, making available large memories and powerful computational resources allow the analysis of problems of unprecedented complexity. The exploitation of the potential offered by these systems highly depends upon the availability of efficient tools devoted to the solution of specific problems. The paper describes a distributed approach to the analysis of large GSPN models whose applicability to real systems was often constrained by the explosion in the size of the underlying state space representation. A performing algorithm for distributed construction of large state space graphs generated by GSPN models is described in detail. The subsequent distributed numerical solution of the Markov chain is then presented and discussed, along with its current limitations. The implementation of the complete distributed solution tool is integrated with the well known GreatSPN package. The use of the widespread MPI Message Passing library makes the tool portable on a large class of distributed and parallel architectures. Performance results in the case of nets with large stale space cardinalities are discussed, considering an experimental low-cost, general purpose PC cluster.

ARGO prototype vehicle

Publisher Summary This chapter presents the experience of the ARGO project. The main target of the ARGO project is the development of an active safety system with the ability to act as an automatic pilot for a standard road vehicle also. In 1997, the ARGO prototype vehicle was set up with sensors and actuators, and the first version of the GOLD software system—able to locate one lane marking and generic obstacles on the vehicles path—was installed. In June 1998, the vehicle underwent a major test to analyze the complete equipment. The analysis of this test enabled the improvement of the system. The current implementation of the GOLD system, featured by enhanced lane detection abilities and extended obstacle detection abilities, such as the detection of leading vehicles and pedestrians are also presented in this chapter.

The PAPRICA SIMD array: Critical reviews and perspectives

The PAPRICA project started in 1988 as an experimental VLSI architecture devoted to the efficient computation of data with two-dimensional structure. The main goal of the project is to develop a subsystem that could operate as an attached processing unit to a standard workstation and in perspective as a specialized processing module in dedicated systems devoted to low level image analysis, cellular neural networks emulation, DRC algorithms. The architecture has been extensively used for basic low level image analysis tasks up to optical flow computation and feature tracking, showing encouraging performance even in the first prototype version. The authors discuss the actual implementation and present a critical analysis of the project, allowing to identify some crucial points of PAPRICA design (and of array processors in general) that must be carefully considered in the case of redesign.<<ETX>>

Design and Implementation of the PAPRICA Parallel Architecture

In this paper PAPRICA, a massively parallel coprocessor devoted to the analysis of bitmapped images is presented considering first the computational model, then the architecture and its implementation, and finally the performance analysis. The main goal of the project was to develop a subsystem to be attached to a standard workstation and to operate as a specialized processing module in dedicated systems. The computational model is strongly related to the concepts of mathematical morphology, and therefore the instruction set of the processing units implements basic morphological transformations. Moreover, the specific processor virtualization mechanism allows to handle and process multiresolution data sets. The actual implementation consists of a mesh of 256 single bit processing units operating in a SIMD style and is based on a set of custom VLSI circuits. The architecture comprises specific hardware extensions that significantly improved performances in real-time applications.