Abstract not found

When enacting a web service orchestration defined using the Business Process Execution Language (BPEL) we observed various safety property violations. This surprised us considerably as we had previously established that the orchestration was free of such property violations using existing BPEL model checking techniques. In this paper, we describe the origins of these violations. They result from a combination of design and deployment decisions, which include the distribution of services across hosts, the choice of synchronisation primitives in the process and the threading configuration of the servlet container that hosts the orchestrated web services. This leads us to conclude that model checking approaches that ignore resource constraints of the deployment environment are insufficient to establish safety and liveness properties of service orchestrations specifically, and distributed systems more generally. We show how model checking can take execution resource constraints into account. We evaluate the approach by applying it to the above application and are able to demonstrate that a change in allocation of services to hosts is indeed safe, a result that we are able to confirm experimentally in the deployed system. The approach is supported by a tool suite, known as WS-Engineer, providing automated process translation, architecture and model-checking views.

Abstract — BPEL is the de facto standard for business process modeling in today’s enterprises and is a promising candidate for the integration of business and Grid applications. Current BPEL implementations do not provide mechanisms to schedule service calls with respect to the load of the target hosts. In this paper, a solution that automatically schedules workflow steps to underutilized hosts and provides new hosts using Cloud computing infrastructures in peak-load situations is presented. The proposed approach does not require any changes to the BPEL standard. An implementation based on the ActiveBPEL engine and Amazon’s Elastic Compute Cloud is presented. I.

In grid workflow systems, temporal correctness is critical to assure the timely completion of grid workflow execution. To monitor and control the temporal correctness, fixed-time constraints are often assigned to a grid workflow and then verified. A checkpoint selection strategy is used to select checkpoints along grid workflow execution for verifying fixed-time constraints. The problem of existing representative strategies is that they do not differentiate fixed-time constraints as once a checkpoint is selected, they verify all fixed-time constraints. However, these checkpoints do not need to be taken for those constraints whose consistency can be deduced from others. The corresponding verification of such constraints is consequently unnecessary and can severely impact the efficiency of overall temporal verification. To address the problem, in this paper, we develop a new temporal dependency based checkpoint selection strategy which can select checkpoints according to different fixed-time constraints. With our strategy, the corresponding unnecessary verification can be avoided. The comparison and experimental simulation further demonstrate that our new strategy can improve the efficiency of overall temporal verification significantly over the existing representative strategies.

Abstract — BPEL is the de-facto standard for business process modeling in today’s enterprises and is a promising candidate for the integration of business and Grid applications. While BPEL works well for traditional web services, it has a number of drawbacks with respect to the more complex world of WSRFbased Grid computing, especially where security is concerned. In this paper, a solution that extends the BPEL security approach to encompass secure Grid application interactions is presented. The proposed approach is capable of handling both web service and Grid service resources and their corresponding security mechanisms. The BPEL language is extended by security-related settings. An implementation of a GSI-compliant BPEL engine that can also manage the lifetime of proxy certificates is presented. I.

Abstract — The widespread deployment of mobile devices like PDAs and mobile phones has created a vast computation and communication platform for pervasive computing applications. However, these devices feature an array of incompatible hardware and software architectures, discouraging ad-hoc interactions among devices. The Business Process Execution Language (BPEL) allows users in wired computing settings to model applications of significant complexity, leveraging Web standards to guarantee interoperability. However, BPEL’s inflexible communication model effectively prohibits its deployment on the kinds of dynamic wireless networks used by most pervasive computing devices. This paper presents extensions to BPEL that address these restrictions, transforming BPEL into a versatile platform for interoperable pervasive computing applications. We discuss our implementation of these extensions in Sliver, a lightweight BPEL execution engine that we have developed for mobile devices. We also evaluate a pervasive computing application prototype implemented in BPEL, running on Sliver. I.

Abstract not found

Abstract. Grid computing aims to create an accessible virtual supercomputer by integrating distributed computers to form a parallel infrastructure for processing applications. To enable service-oriented Grid computing, the Grid computing architecture was aligned with the current Web service technologies; thereby, making it possible for Grid applications to be exposed as Web services. The WSRF set of specifications standardized the association of state information with Web services (WS-Resource) while providing interfaces for the management of state data. Key to the realization of the benefits of Grid computing is the ability to integrate WS-Resources to create higher-level applications. The Business Process Execution Language (BPEL) is the leading standard for integrating Web services and as such has a natural affinity to the integration of Grid services. In this paper, we share our experience on using BPEL to integrate, create, and manage WS-Resources that implement the factory pattern. We use a Bioinformatics application as a case study to show how BPEL can be used to orchestrate Grid services. The execution environment for our case study comprises the Globus Toolkit as the Grid middleware and the ActiveBPEL as the BPEL engine. To the best of our knowledge, this work is among the handful approaches that successfully use BPEL for orchestrating WSRF-based services and the only one that includes the discovery and management of instances.

Abstract. Grid computing aims to create an accessible virtual supercomputer by integrating distributed computers to form a parallel infrastructure for processing applications. To enable service-oriented Grid computing, the Grid computing architecture was aligned with current Web service technologies. Thereby making it possible for Grid applications to be exposed as Web services. The WSRF set of specifications standardized the association of state information with Web services (WS-Resource) while providing interfaces for the management of state data. Key to the realization of the benefits of Grid computing is the ability to integrate WS-Resources to create higher-level applications. The Business Process Execution Language (BPEL) is the leading standard for integrating Web services and as such has a natural affinity to the integration of Grid services. In this paper, we share our experience on using BPEL to integrate, create, and manage WS-Resources that implement the factory/instance pattern.

Web services are increasingly used in inter-organizational settings. If an organization depends on the service quality provided by another organization it often enters into a bilateral service level agreement (SLA) to precisely determine service quality and permitted service use. SLAs then also determine penalty payments as risk mitigation against poor service quality and overuse of the service. Once these agreements are entered into, it becomes necessary to monitor for both poor service quality and also abuse of the provision beyond the agreed limits. We address the question of how service level agreements can be monitored efficiently and automatically. We show how timeliness constraints, such as latency, throughput, availability and reliability, in formal service level agreements can be translated into timed automata. We attach time stamps to SOAP messages and consider these messages as timed letters. We are then able to reduce the question of detecting SLA violations to acceptance of timed words by the timed automata that have been derived from the SLA. Acceptance of a timed word by a timed automaton can be decided in polynomial time and because the timed automata can operate while SOAP messages are exchanged at run-time there effectively is only a linear run-time overhead. We evaluate the efficiency and scalability of this approach using a large-scale case study in a service-oriented computational grid. 1.