Patterns: Broker Interactions for Intra- and Inter-enterprise

Chapter 8. Router solutions using Web Services Gateway 161

8.4 Design guidelines

As the solution was being designed, the following topics were considered.

SOAP messaging style

SOAP provides support for both RPC style Web services and document-style

Web services. In RPC style, Web services are invoked using remote method

calls. In document-style messaging, Web Services are invoked by sending a

complete well-formed document describing the task to be performed, and

possibly, some parametric data.

These are some advantages of SOAP RPC-based Web services:

򐂰 They are simpler to develop than SOAP message-oriented messaging.

򐂰 They use a higher level API.

򐂰 They support strong typing: all calls must conform to the method signature.

The disadvantages of RPC-based SOAP messaging are:

򐂰 Higher coupling between the Web service requester and provider because

the requester to provider binding includes both methods and parameters.

On the other hand, when using document-style Web services, the XML

document is arbitrary. This style is more flexible and can be used to send

one-way messages without needing a response (unlike RPC-style) but involves

more work for the developer.

Prior to the Web Services Gateway provided with IBM WebSphere Application

Server V5.0.2, RPC-style SOAP messages were required. With V5.0.2, support

for document-style messages was added. If you are using the Apache SOAP

Channel, then the SOAP message format must be RPC style. To handle

Document style SOAP messages, use the SOAP/HTTP channel (which supports

both RPC style and Document style SOAP messages). We used the RPC-based

mechanism in our sample solution.

SOAP encoding style

In addition to the messaging style, the SOAP encoding style should be

considered. Message parts can be encoded using encoding rules (“encoded”), or

may reference a concrete schema definition (“literal”).

WS-I has stated a preference for the use of literal, non-encoded XML.

162 Broker Interactions for Intra- and Inter-enterprise

SOAP caching

Using WebSphere Application Server dynamic caching to cache SOAP

messages can significantly reduce the overhead of Web services. A Web service

is a candidate for caching if its requests can be grouped into classes based on

identifiers, and if the Web service's responses do not contain arbitrarily changing

information based on the system state or time.

Caching a SOAP message is not as easy as putting it in a HashMap. You need to

determine what makes two SOAP request identical. Only then can a caching

framework determine when to send a client a cached response instead of letting

the request propagate further into the system.To decide if two SOAP request are

identical, you could have to look at the SOAP Body, or at the SOAP Body and

some combination of SOAP header values.

Message optimization

The performance of an application based on Web services is affected by three

factors:

򐂰 Network transmission time.

򐂰 The time it takes to handle the messages, including XML parsing, flow

management, invocation of the service and the encoding of the final response

򐂰 The time the service itself takes to execute

The two first factors can be improved by optimizing the number, size, and

structure of the messages you use. For example:

򐂰 Don’t pass parameters that you don’t need.

򐂰 Don’t use two or more invocations when you can do the same operation

implementing a more complex service. A good example for this could be:

Instead of repeatedly using an operation that returns the price of a product,

implement a service that returns the price for a list of products.

The third factor can be improved using a good caching system, as discussed

previously.

Security

Security is certainly important in an intra-enterprise environment, but becomes

crucial in an inter-enterprise environment. General security guidelines are:

򐂰 Use https when invoking external services.

The Web Services Gateway can invoke Web services that include https:// in

their addresses, if the Java and WebSphere security properties have been

configured to allow it.