9.8 Global XML Web Services Architecture (GXA)

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As the various Web service technologies gain hold, there are a number of holes in the current standards as different organizations innovate and produce new solutions. To bridge this ever-expanding gap, Microsoft has worked with IBM to design an architectural sketch to fill in a number of areas, including security, routing, reliable messaging, and transactions. This architecture, called GXA, was presented to a World Wide Web Consortium workshop in April 2001. The specifications within GXA represent what is called a composable architecture, in that the suggested specifications are used alongside other specifications already accepted within the standards body.

The design of GXA is based on some fundamental themes:

• GXA is designed for broad coverage of a range of Web services solutions, including business-to-business, enterprise application integration, and business-to-consumer.

• GXA employs a modular approach, so that features can be employed when needed but without the overhead of carrying unneeded functionality. In addition, when new features are developed they can be added as required.

• GXA does not need a centralized server or administration since it is a federated service. It is technology-independent and does not need specific implementation technology at the message end points.

• GXA is based on standards such as SOAP, WSDL, and UDDI and Microsoft is proposing to keep GXA in the realm of industry standards.

9.8.1 GXA Security

Undoubtedly, security is one of the most important aspects of Internet commerce. With the impending proliferation of Web services, by definition, heterogeneous systems will be connecting using a range of technologies and implementations that will need to trust each other-or the concept of Web services will collapse.

WS-Security describes the process of using the standard W3C security specifications, XML Signature and XML Encryption, to ensure that SOAP messages are secure. WS-Security is a straightforward, stateless extension to SOAP that explains how credentials are placed within SOAP messages.

WS-License is a mechanism that uses existing license formats, such as X.509 and Kerberos tickets, as WS-Security credentials. Its extensibility model is designed to accommodate new license formats as they become incorporated into the specification.

9.8.2 GXA Routing

The variety of communication technologies in use on the Internet means that SOAP messages need to be transmitted across a number of technical boundaries. WS-Routing and WS-Referral support this.

WS-Routing is a stateless extension for SOAP that allows messages to be sent asynchronously over a range of communication transports, including TCP, UDP, and HTTP. It also includes a mechanism for two-way messaging.

WS-Referral allows a SOAP node to pass on its processing responsibility to another SOAP node.

9.8.3 Reliable Messaging

Transmission errors are part and parcel of the Internet due to its complex nature. For commerce to succeed in this environment it is critical that messages sent from one place to another arrive on time and intact. This protocol provides a guarantee of delivery with an easy-to-use error-handling model, so that developers are not buried in the detail of messaging semantics. There are built-in messaging guarantees, so that end-to-end delivery is ensured and messages are not lost or duplicated.

9.8.4 Transaction Management

Transactions-atomic units of work-are difficult to manage in a stateful networking environment. Couple transactions with the stateless Internet, and problems will occur. In many situations, a far looser transaction model is preferred and will still enable the business to be effective. GXA provides the architecture for building and deploying transaction models across the Internet.

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