Andrew L. Wendelborn

Process Networks as a High-Level Notation for Metacomputing

Our work involves the development of a prototype Geographical Information System (GIS) as an example of the use of process networks as a well-defined high-level semantic model for the composition of GIS operations. Our Java-based implementation of this prototype is known as PAGIS (Process network Architecture for GIS).

Geographic Information Systems Application on an ATM-based Distributed High Performance Computing System

We present a distributed geographic information system (DGIS) built on a distributed high performance computing environment[1] using a number of software infrastructural building blocks and computational resources interconnected by an ATM-based broadband network. Archiving, access and processing of scientific data are discussed in the context of geographic and environmental applications with special emphasis on the potential for local-area weather, agriculture, soil and land management products. In particular, we discuss the capabilities of a distributed high-performance environment incorporating: high bandwidth communications networks such as Telstras Experimental Broadband Network (EBN)[3]; large capacity hierarchical storage systems; and high performance parallel computing resources.

Component-based stream processing "in the cloud"

In earlier work, we reported on modeling of stream processing in terms of distributed components (as exemplified in the EU CoreGrid project ProActive), showing how a stream processing system can be built from components in composition, with dynamic reconfiguration and distributed management of the streams. In this paper, we introduce the Web Service Stream Deployer (WSSD), for the remote establishment and deployment of streams across widely distributed resources, allowing a user to set-up, control and reconfigure a stream remotely and dynamically. We demonstrate this concept with streams on a cloud testbed, using Nimbus cloud infrastructure at the University of Chicago. In particular, we show that our web-services based WSSD exhibits minimal adverse latency effect when used over an intercontinental network to manipulate, from our client in Australia, a cloud-based stream in the USA; we believe that this represents a useful mode of remote interaction with cloud-based applications. We outline some ideas in scheduling of cloud-based streams; we present a model of interaction with Gridbus, a widely used framework for exploring different scheduling algorithms (such as economic scheduling), whereby scheduling criteria expressed in Gridbus can be used to automatically deploy stream components.

Distributed, parallel Web service orchestration using XSLT

GridXSLT is an implementation of the XSLT programming language designed for distributed Web service orchestration. Based on the functional semantics of the language, it compiles programs into dataflow graphs which can be efficiently executed across a collection of machines in a cluster or grid environment. Calls to Web services can be made using the standard function call semantics provided by the language, and occur in parallel using the dataflow model of computation. The programmer is not required to explicitly specify the parallelism, as the details of how programs are scheduled and executed in a distributed environment are abstracted away by the runtime engine. XSLT provides a higher level programming model than many other approaches to Web services composition; we explore its use here as a means of easing the task of orchestrating the interactions between services. In addition to the normal XSLT syntax, our system also supports programs written in XSLiTe, an alternative syntax we have developed which uses more concise representations of language constructs, increasing the ease of development, and bringing code readability closer to that of traditional programming languages. Our goal is to ease the construction of applications based on Web services composition, such as those used in eScience and other fields in which service oriented architectures are prominent

The PAGIS grid application environment

Although current programming models provide adequate performance, many prove inadequate to support the effective development of efficient Grid applications. Many of the hard issues, such as the dynamic nature of the Grid environment, are left to the programmer. We are developing a programming model that incorporates a familiar, formal computational model and a reflective interface. The programming model, called PAGIS, provides a desirable abstract computer with an interface to introduce and customize Grid functionality. Using PAGIS, an application programmer constructs applications that are implicitly parallel and distributed transparently. This paper describes the basic components of the PAGIS framework for constructing and executing applications, and the reflective techniques to customize applications for computation on the Grid.

Alias analysis for exceptions in Java

We propose a flow-sensitive alias analysis algorithm that computes safe and efficient alias sets in Java. For that, we propose a references-set representation of aliased elements, its type table, and its propagation rules. Also, for an exception construct, we consider try/catch/finally blocks as well as potential exception statement nodes while building a control flow graph. Finally, for the safe alias computation on a control flow graph, we present a structural order traverse of each block and node.

Improving data transfer performance of web service workflows in the cloud environment

Web Service Data Forwarding (WSDF) is a framework for centralized web service workflow, in which the intermediate result from a previous service is treated as a resource of the composite service and can be directly used by its subsequent service, without sending back to the centralized control centre. We carried out a test of the WSDF framework within a web service workflow, in which the service providers are located in the {Science Cloud}, provided by the Nimbus cloud infrastructure. The experiment shows that, in the cloud environment, the WSDF framework has significant performance advantage over normal web service framework for workflows with large data transfer.

Web services workflow with result data forwarding as resources

Under a centralized workflow model, distributed data transfer between consecutive services in a Web service workflow can save network bandwidth and avoid the centralized workflow engine being overloaded. The proposed Web Service Data Forwarding (WSDF) framework harnesses the Web Service Resource Framework (WSRF) to meet this requirement. A WSDF compliant service in a workflow can forward the result to its successor service for future usage. This result forwarding function is implemented at the WSDF server level and is transparent to functional services. Our prototype system has shown that this framework can save data transfer time and significantly improve the overall performance of some workflows.

Binary Data Transfer Performance over High-Latency Networks Using Web Service Attachments

One of the objectives of e-Research is to help scientists to accomplish their research, including scientific experiments, more effectively and efficiently. Web services provide communication between different platforms by using standardized SOAP message protocols. Hence, it is often productive to implement web service interfaces for the integration of experimental infrastructure into a collaborative e-Science framework. In this context, transfer and management of experimental data is an important problem. SOAP messaging is primarily oriented towards XML character data, with binary data transmitted with, for example, a base64 character encoding. However, as scientific experiments often generate binary data, transferring binary information by applying an encoding algorithm can slow down the performance of the system. The notion of web service attachment, has been introduced to solve this problem. In this paper, we illustrate how we use web services with attachments to improve binary data transfer performance. We present results of tests, using Axis2 and XFire APIs, conducted over a campus IAN, an inter-city WAN, and an intercontinental WAN. We also make some comparison with the use of GridFTP.

A Data-Aware Resource Broker for Data Grids

The success of grid computing depends on the existence of grid middleware that provides core services such as security, data management, resource information, and resource brokering and scheduling. Current general-purpose grid resource brokers deal only with computation requirements of applications, which is a limitation for data grids that enable processing of large scientific data sets. In this paper, a new data-aware resource brokering scheme, which factors both computational and data transfer requirements into its cost models, has been implemented and tested. The experiments reported in this paper clearly demonstrate that both factors should be considered in order to efficiently schedule data intensive tasks.