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Chapter 19 Web services

Contents

19.1 Introduction

19.2 Web services

SOAP; A comparison of web services with the distributed object model; The use of SOAP with Java; Comparison of web services with CORBA;

19.3 Service descriptions and IDL for web services

19.4 A directory service for use with web services

19.5 XML security

19.6 Coordination of web services

19.7 Case study: the Grid

The World-Wide Telescope - a grid application; The characteristics of a family of data-intensive scientific applications; Open grid services architecture; Some examples of grid applications; The Globus toolkit;

19.8 Summary

Ouline of Chapter

A web service provides a service interface enabling clients to interact with servers in a more general way than web browsers do. Clients access the operations in the interface of a web service by means of requests and replies formatted in XML and usually transmitted over HTTP. Web services can be accessed in a more ad hoc manner than Corba-based services, enabling them to be more easily used in Internet-wide applications.

Like CORBA and Java, the interfaces of web services can be described in an IDL. But for web services, additional information including the encoding and communication protocols in use and the service location need to be described.Users require a secure means for creating, storing and modifying documents and exchanging them over the Internet. The secure channels of TLS do not provide all of the necessary requirements. XML security is intended to breach this gap.

The Grid is the name used to refer to a middleware platform based on web services and designed for use by large dispersed groups of users with massive data resources that require substantial processing. The astronomers’ World-Wide Telescope is a typical grid application for scientific collaboration. The characteristics of data-intensive scientific applications are derived from a study of the World-Wide Telescope. These characteristics lead to a set of requirements for a grid architecture.