Mediation primitives

Mediation components operate on message flows between service components. The capabilities of a mediation component are implemented by mediation primitives, which implement standard service implementation types.

A mediation component has one or more flows. For example, one for request and one for reply.

WebSphere Process Server supports a supplied set of mediation primitives, which implement standard mediation capabilities for mediation modules deployed into WebSphere Process Server. If you need special mediation capabilities, you can develop your own custom mediation primitives.

A mediation primitive defines one "in" operation that processes or handles messages that are represented by service message objects (SMO). A mediation primitives can also define "out" operations that send messages to another component or module.

Figure 1. Mediation module containing three mediation primitives
Mediation primitives in a mediation module

Mediation primitives typically function at the level of a single operation, with possible mediation of the request and response. In some cases, you can specify mediation primitives down to the level of a single parameter on an operation. For example, selectors can operate at the operation level or parameter level.

You can use WebSphere Integration Developer to graphically model and assemble mediation components from mediation primitives, and assemble mediation modules from mediation components.

Supported mediation primitives

The following set of mediation primitives are supported by WebSphere Process Server:
Custom Mediation
Runs custom logic. The Custom Mediation primitive can call an external Service Component Architecture (SCA) component that you provide.
  • The operation that is called must be a two-way operation.
  • The target SCA component must exist in the same mediation module as the Custom Mediation primitive.
Database Lookup
Modifies messages, using information from a user-supplied database.
  • You must set up a database, datasource and any server authentication settings for the Database Lookup mediation primitive to use.
  • The Database Lookup mediation primitive can read from only one table.
  • The specified key column must contain a unique value.
  • The data in the value columns must be either a Java primitive or a Java String (or be able to be cast to a Java primitive or a Java String).
Endpoint Lookup
Allows for dynamic routing of requests, by searching for service endpoints in a repository.
  • Service endpoint information is retrieved from a WebSphere Service Registry and Repository (WSRR), which can be local or remote.
  • You can make registry changes from the administrative console.
Event Emitter
Enhances monitoring, by emitting events from within a mediation flow.
  • The events are sent in the form of Common Base Events (CBE) and are sent to a Common Event Infrastructure (CEI) server.
  • To fully utilize Event Emitter information, event consumers need to understand the structure of the CBE. The CBE has an overall schema but this does not model the application specific data, contained in the extended data elements. To model the extended data elements, the WebSphere Integration Developer tools generate a CEI event catalog definition file for each of the configured Event Emitter mediation primitives. Event catalog definition files are export artifacts that are provided to help you, they are not used by WebSphere Integration Developer or by the WebSphere Process Server runtime. You should refer to the event catalog definition files when you create applications to consume Event Emitter events.
  • You can specify other monitoring from WebSphere Process Server. For example, you can monitor events to be emitted from imports and exports. What the Event Emitter mediation primitive does is let you send events from inside a mediation flow component. You can then view Event Emitter events using the CBE browser on WebSphere Process Server.
Fail
Generates a failure in the flow.
Message Element Setter
Provides a simple mechanism for setting the content of message headers or bodies, it does not change the type of the message.
Message Filter
Routes messages down different paths, based on the message content.
Message Logger
Logs messages in a database. The messages are stored as XML, therefore data can be post-processed by XML-aware applications.
  • The database schema is defined by IBM.
  • On distributed platforms, the default installation of WebSphere Process Server creates a stand-alone application server, and a Cloudscape database and datasource. By default, WebSphere Integration Developer configures Message Logger mediation primitives to use this Cloudscape database. WebSphere Process Server also provides a script, called createMessageLoggerResource.jacl, that creates a Cloudscape database.
  • You can use the coreDBUtilty command to create a DB2 message logging database on a remote z/OS system.
  • If you want to create your own database and datasource, using the administrative console, then WebSphere Process Server provides data definition language (ddl) files that describe the table schema. The Table.ddl files are stored in: install_root/util/EsbLoggerMediation/database_ type/Table.ddl. Where database_ type refers to the type of database, for example, CLOUDSCAPE_V50. If you create your own database and want to use the default JNDI name for your datasource, then you must remove the default datasource.
Stop
Stops a particular path in the flow, without generating an exception.
XSLT
Transforms messages.
  • The XSLT mediation primitive can change the headers or the body of your messages.
  • You transform messages using an XSLT (Extensible Stylesheet Transformations) 1.0 transformation. The transformation operates on an XML serialization of the message.
SplitPath
Select the target service (or another mediation), route to a specific target, modify the routing path ...
BOMapper
Select the target service (or another mediation), route to a specific target, modify the routing path ...

Last updated: Thu 26 Oct 2006 10:30:05

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