Chapter List

Overview

Several efforts to design globally distributed computing systems have converged to the principles of message-centric, service-oriented architectures. As realized through several Web Service specifications, these provide the scaling, robustness, and reliability for delivering distributed capabilities that collectively form virtual organizations. Service architectures are based a clean separation between service implementations and their communication patterns. In this article, we examine several consequences of this separation. First, services should exist on a general purpose, software messaging substrate. Services (and their containers) inherit various qualities of service directly from this substrate: we implement message level security, reliability, events, and notifications in the message routing middleware. Second, all communications involving services should be treated as messages. This applies not only to remote procedure call-style messages and notifications, but to streaming data as well. Finally, services are often domain-specific, but collective applications are cross-domain. Using message-based Geographical Information Systems as an example, we illustrate how a Grid of services is really a Grid of Grids: a composition of capabilities developed independently of specific end applications.

1. Introduction

As standards such as SOAP 1.2, WSDL 2.0, and...