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There are two primary types of web services styles: RPC-oriented and documentoriented. The RPC style of web services was popular initially, but more recently the pendulum has swung in the direction of document-oriented web services. One reason for this shift is that you can make better use of an XML schema with document-oriented web service. To learn some of the differences between RPC and document-oriented web services, visit http://expertanswercenter.techtarget.com/eac/knowledgebaseAnswer/0,295199,sid63_gci984152,00.html. The messaging style for a web service may be either literal or encoded. When you use literal, the messages are exchanged with plain XML. However, an encoded message includes an external rule about how to decode the message. The receiver of the message has to decode the message by using the decoding attribute. The WS-I Basic Profile 1.1 doesn t support encoded messages.

The most popular combination of web service style and messaging style is document/literal. This is because the WSI Basic Profile only supports the document/literal combination for maximum interoperability between platforms. Document/ literal-style messages are constrained by an XML schema. The schema can reside in the WSDL or can be referred to with an URI. The end result is that you can manage the structure of your message in the same way that DBAs manage table definitions with versioning. The RPC/encoded combination puts the schema in the actual message itself, which makes it much more tightly coupled to the message. Stick with what the WSI Basic Profile supports (document/literal), and your web services will enjoy maximum interoperability and acceptance by the widest possible audience.

Only a few standard approaches exist for building a web service. These approaches are independent of whatever tools you may be using but are somewhat specific to the SOAP style of building web services. Bottom up The bottom-up strategy is the most popular approach to developing a web service. It allows you to reuse your investments by exposing your existing applications. For example, ActionBazaar is an existing application with proven business value. Competitive pressure is moving ActionBazaar to expose some of this business functionality as web services. The implementation class already exists. All that is needed is to create a WSDL and expose the implementation class as a web service. Java EE 5 allows either POJOs or stateless EJBs to be exposed as web services. Most application servers provide tools and utilities to generate WSDL from existing Java classes. Top down Top down is the correct way to build any new web service, and is often termed the pure approach to building a web service. Also known as contract first web services, this approach starts with the WSDL (the contract) by defining operations, messages, and so forth. Then you build the endpoint interface, and finally the implementation class. If you are building a web service from scratch, we recommend that you follow this approach. Most application servers provide development tools to create WSDL and then provide the ability to generate a Java class from the WSDL. Just add your business logic to the generated class, stir in a little water,

bake at 350 degrees for 5 minutes, and your new web service should be ready to pop out of the oven! Meet in the middle In the meet-in-the-middle approach, you start with both the WSDL and implementation class and wire the WSDL with the implementation class. This is harder to implement and can be difficult to maintain since you have to pay a lot more attention to keeping things in synch. We recommend you avoid this approach if at all possible. The movement from the bottom-up to the top-down approach of building SOAP-based web services is still in progress. Many IT shops are still using bottom up as the tool support is by far the best for this approach, and because web services have been limited to use within the enterprise for many industries. As interoperability between companies and technologies increases in value, we expect top down, specifically contract first web services, to become the widest adopted approach to defining and building web services. Now that you are aware of the approaches to building SOAP-based web services, what protocols and standards exist to assist you in such an endeavor The next section points you down the path that so many have helped to build: the path to the Java web services platform.