Yudith Cardinale

CPN-TWS: a coloured petri-net approach for transactional-QoS driven Web Service composition

In this paper, we address the issue of selecting and composing Web Services (WSs) considering functional and Quality of Service (QoS) requirements combined with transactional properties. We formalise the WS functional, QoS and transactional properties as well as the WS Composition problem. We have extended Coloured Petri Net (CPN) formalism to incorporate transactional WSs properties in the composition process. We present and prove our CPN Transactional WS (CPN-TWS) selection algorithm that satisfies the user query functional conditions expressed as input and output attributes, QoS requirements represented by weights over criteria, and transactional properties expressed as a risk level. The result of our algorithm is a CPN corresponding to a Transactional Composite WS whose WS components locally optimise the QoS. We present experimental results to study the performance and the efficiency of our selection algorithm compared with an exhaustive one.

Modeling dynamic recovery strategy for composite web services execution

During the execution of Composite Web Services (CWS), a component Web Service (WS) can fail and can be repaired with strategies such WS retry, substitution, compensation, roll-back, replication, or checkpointing. Each strategy behaves differently on different scenarios, impacting the CWS QoS. We propose a non intrusive dynamic fault tolerant model that analyses several levels of information: environment state, execution state, and QoS criteria, to dynamically decide the best recovery strategy when a failure occurs. We present an experimental study to evaluate the model and determine the impact on QoS parameters of different recovery strategies; and evaluate the intrusiveness of our strategy during the normal execution of CWSs.

Web Service Selection for Transactional Composition

In this work we address the issue of selecting and composing Web Services (WSs) considering functional requirements and transactional properties. We formalize the WS composition problem using the user query, the transactional properties of WSs and the composite WSs definition. We extends Colored Petri Net (CPN) formalism to incorporate transactional WSs properties. We present a CPN-WS selection algorithm that satisfies the user query functional conditions expressed as input and output attributes, and transactional properties expressed as a risk level. The result of our algorithm is a Colored Petri-Net allowing to execute a transactional composite WS.

Techniques to Produce Optimal Web Service Compositions

As Web Services proliferate, it becomes more difficult to find a service that can perform a given task, and a coordination of several services may be required. We present two algorithms to identify orderings of Web Service compositions. These algorithms follow different strategies to prune the space of possibilities while minimizing the evaluation cost. The first one, DP-BF, combines a best first strategy with a dynamic-programming technique and produces good Web Service compositions by exploring a small portion of the search space. The second one, PT-SAM, adapts a petri-net unfolding algorithm and tries to find a desired marking from an initial state. We conducted an experimental study to evaluate the behavior of DP-BF and PT-SAM comparedto SAM and to the exhaustive solution. Our experimentsshow that the quality of the compositions identified by ouralgorithms are close to the optimal solution produced by theexhaustive algorithm, while the optimization time is close to the time required by SAM to identify a solution.

Parallel checkpointing on a grid-enabled java platform

This article describes the implementation of checkpointing and recovery services in a Java-based distributed platform. Our case study is suma, a distributed execution platform implemented on top of Grid services. suma has been designed for execution of Java bytecode, with additional support for parallel processing. suma middleware is built on top of commodity software and communication technologies, including Java, Corba, and Globus services. The implementation of suma that runs on top of Globus services is called suma/g.

FaCETa: Backward and Forward Recovery for Execution of Transactional Composite WS

In distributed software contexts, Web Services (WSs) that provide transactional properties are useful to guarantee reliable Transactional Composite WSs (TCWSs) execution and to ensure the whole system consistent state even in presence of failures. Failures during the execution of a TCWS can be repaired by forward or backward recovery processes, according to the component WSs transactional properties. In this paper, we present the architecture and an implementation of a framework, called FaCETa, for efficient, fault tolerant, and correct distributed execution of TCWSs. FaCETa relies on WSs replacement, on a compensation protocol, and on unrolling processes of Colored Petri-Nets to support failures. We implemented FaCETa in a Message Passing Interface (MPI) cluster of PCs in order to analyze and compare the behavior of the recovery techniques and the intrusiveness of the framework.

Implementation of a CORBA-Based Metacomputing System

The access to distributed high performance computing facilities for execution of Java programs has generated considerable interest. A metacomputing system, or metasystem, allows uniform access to heterogeneous resources. Our case study is SUMA, a metasystem defined as a set of corba components, offering services for execution of both sequential and parallel applications. This document describes the most important aspects of suma design in terms of corba services. We present some experimental results related to execution overhead in a campus-wide environment.

Checkpointing Facility on a Metasystem

A metasystem allows seamless access to a collection of distributed computational resources. Checkpointing is an important service in high throughput computing, especially for process migration and recovery after system crash. This article describes the experiences on incorporating checkpointing and recovery facilities in a Java-based metasystem. Our case study is suma, a metasystem for execution of Java bytecode, both sequential and parallel. This paper also shows preliminary results on checkpointing and recovery overhead for single-node applications.

A Java-Based Distributed Genetic Algorithm Framework

Distributed genetic algorithm (DGA) is one of the most promising choices among the optimization methods. In this paper we describe DGAFrame, alpha flexible framework for evolutionary computation, written in Java. DGAFrame executes GAs across a range of machines communicating through RMI network technology, allowing the implementation of portable, flexible GAs that use the island model approach. Each island can be configured independently from others providing the implementation of heterogeneous DGAs. To evaluate the performance of DGAFrame, we implemented the protein structure prediction problem and compare the DGA execution to its sequential counterpart through quality of solution. We also measure the computation to communication ratio and results show that the proposals consistently outperform equivalent sequential GAs.

FACETA*: Checkpointing for Transactional Composite Web Service Execution based on Petri-Nets

Abstract Failures during the execution of Transactional Composite Web Services (TCWSs) can be repaired by forward or back–ward recovery processes, according to the component WSs transactional properties. In previous works, we presented TCWS fault tolerant execution approaches relying on WSs replacement, on a compensation protocol, and on unrolling processes of Colored Petri-Nets (CPNs) to support forward and backward recovery. We represent a TCWS and its corresponding backward recovery process by CPNs. Even though these recovery processes ensure system consistency, backward recovery means that users do not get the desired answer to their queries and forward recovery could imply long waiting time for users to finally get the desired response. In this paper, we present an alternative fault tolerant approach in which, in case of failures, the unrolling process of the CPN controlling the execution of a TCWS is check–pointed and the execution flow goes on as much as it is possible. In this way, users can have partial responses as soon as they are received and can re-submit the checkpointed CPN to re-start its execution from an advanced point of execution (checkpoint). We present the checkpointing algorithm integrated to our previous work.