STRATEGIES

October 4, 2004

WS Standards

Let’s assume that you do need to build automated, but loosely coupled, connections within your enterprise or with your customers. Which of the Web services standards should you examine? Here is a brief summary focusing on what those that are widely deployed actually offer (or for more detail see xml.coverpages.org).

HTTP - the common denominator of the World Wide Web, its primary value is that it is almost universally supported, and therefore is the means of choice for moving information between an application requesting a service and the service itself (if no other assumptions can be made). In addition to various well-known limitations with respect to reliable message delivery and security, HTTP has no support for multi-part transactions.

XML - almost universally supported as a way of formatting documents, data, and messages for interchange across diverse systems. A large body of technologies sits on top of the basic XML standard to define data types, perform format transformations, query repositories, and so forth. The primary downside is that XML messages tend to be considerably larger and slower to process than the previous generation of binary data protocols.

The combination of HTTP and XML can provide the entire service infrastructure you may need to provide services over the Web. Indeed, a 2004 Web services report from a well-known analyst group indicates this pair of technologies is so mature as to be off the graph in their “hyperbole sine-wave” chart.

SOAP - originally an acronym for a Simple Object Access Protocol that provided CORBA-like remote method invocations using XML and HTTP, it has evolved the past several years to be more a framework upon which to build higher-level WS-protocols (see below). Nevertheless, its basic remote object access features are widely supported as a way of connecting applications over the Web.

WSDL - defines the specifics of the messages in a SOAP exchange. It is very widely supported by tools designed to receive a WSDL definition of a Web service, and then generate the necessary code and data to invoke that service. For example, Microsoft Excel can import a WSDL description of a service offered by a mainframe enterprise accounting system, and then call the service to populate data in a spreadsheet.

UDDI - often cited as a core Web services specification, it has been far less widely used in practice than SOAP and WSDL. UDDI may be an “ugly ducking” that will be more widely appreciated as it matures, or it may fade away. Opinions on the future of UDDI differ widely.

WS - a large family of specifications defined by an informal consortium including such notables as Microsoft, IBM, BEA and, now, Sun. Only a few of these specifications have been turned over to formal standards organizations. This family includes WS-Security, WS-ReliableMessaging, WS-Coordination, WS-Addressing, WS-Eventing, BPEL4WS, and others.

These standards offer a way to describe and interchange capabilities of enterprise-class message queuing systems, transaction monitors, and business process management systems, but building from the basis of SOAP and WSDL.

Two new proposals — WS-Transfer and WS-Enumeration — are designed to offer off-the-shelf solutions to address very common needs, e.g. a simple Create/Read/Update/Delete API on top of SOAP.

Building Services

Best practices guidelines are still somewhat speculative, but several years of closely following this field leads me to offer the following suggestions:

Michael Champion is a senior technologist at Software AG, Europe’s largest and most established systems software provider. He has been a software developer for 20 years, and has had extensive involvement with the W3C, including co-chairing the Web Services Architecture Working Group. His participation on the W3C’s Document Object Model (DOM) Working Group from 1997 to 2003 included work as an editor of the core XML portion of the DOM Level 1 Recommendation. Champion has authored numerous articles and is a frequent speaker at industry events.

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