Patterns: Broker Interactions for Intra- and Inter-enterprise

Chapter 7. Technology options 141

Message broker services

A message broker is a server-side service in a message-oriented system. It

manipulates the messages it receives, and performs some or all of the following

functions:

򐂰 Routing services:

– Content based

– Publish/subscribe style

– Message flow processing

򐂰 Data transformation (mapping message to other formats) services:

– Syntactic (format driven)

– Semantic (content driven)

򐂰 Security (authentication/authorization, encryption/decryption) services

򐂰 Transactional service (unit of work support)

򐂰 Error handling

򐂰 Service invocation (invoking an external function to process message

payload)

A message flow is a sequence of operations on a message, dependent upon the

message content and the current message flow state. Message flows can be

viewed as

business services, initiated by receiving a message.

If the broker supports the publish/subscribe style of messaging, subscribing

applications can register their topic subscriptions with the broker. Publishing

applications can then send messages to the broker, who will map the topic to the

registered subscribers and forward the message to all interested parties.

A very good example of the messaging system providing an extensive set of the

message broker services is the WebSphere Business Integration Message

Broker product.

7.7 Flow languages

This section discusses the business process languages relevant to the

WebSphere Process Choreographer and WebSphere MQ Workflow Process

Managers:

򐂰 Flow Definition Language (used by WebSphere MQ Workflow)

򐂰 Flow Definition Markup Language (used by WebSphere Process

Choreographer)

򐂰 Business Process Execution Language for Web Services

142 Broker Interactions for Intra- and Inter-enterprise

7.7.1 Flow Definition Language

Flow Definition Language (FDL) is a text based process definition format that

provides an interface between process modeling and development tools, and the

process engine of WebSphere MQ Workflow.

An FDL document describes the make-up of a process flow. Although

theoretically FDL could be written by hand, it is commonly generated using

WebSphere MQ Workflow Buildtime. As FDL became an established standard,

other process modeling and development tools came on the market that were

capable of exporting FDL, thus suitable for use with WebSphere MQ Workflow.

This included third parties such as Holosofx®, who have since been acquired by

IBM. The Holosofx product is now marketed as IBM WebSphere Business

Integration Workbench, and offers facilities to generate FDL.

7.7.2 Flow Definition Markup Language

Despite its name, which sounds similar to FDL, Flow Definition Markup

Language (FDML) is actually based on the Web Services Flow Language

(WSFL) standard introduced by IBM. FDML introduces extensions to the WSFL

standard and is the flow language used to describe a WebSphere Process

Choreographer process.

WebSphere Studio Application Developer Integration Edition uses FDML to

describe WebSphere Process Choreographer business processes.

FDML describes the behavior of the process. It is an XML based format. An

FDML file describes elements of a process such as the flow model, activities,

control links, compensation, messages, and variables.

A sample of an FDML file is shown in Example 7-1.

Example 7-1 Sample FDML file

wf:flowModel autoDelete="true" canRunInterrupted="true"

canRunSynchronous="false" name="EventCompensationProcess"

requiresCompensationSphere="true" validFrom="2003-01-01T12:00:00">

<wf:messageType name="MessageType_11" typeSystem="WSDL2">

<service:messageRef name="processOrderInput"

namespace="http://process.itso.ibm.com/">

<service:import

location="file:com/ibm/itso/process/EventCompensationProcessInterface.wsdl"/>

</service:messageRef>

</wf:messageType>

For more information about FDML, please refer to the IBM Redbook WebSphere

Version 5 Web Services Handbook, SG24-6891.