IBM BPM, V8.0.1, All platforms > Programming IBM BPM > Enterprise Service Bus programming > Mediation flow with mediation policy
Mediation policy usage scenarios
These scenarios show how you can make your mediation flows more responsive and easier to change.
Lookup from different tables in a database
In this example a message that flows through a IBM BPM mediation is updated with information from a database. Depending on the context of the message, information might be required from different database tables and the system can be expanded later to extract from further tables.
The context for a message can vary with an employee's department, and additional departments can be created in the future. In the database, data about employees is held in different schemas depending on the department.
For example, there can be ACCOUNTS, HUMANRESOURCES, WAREHOUSE, and TRANSPORT schemas. Each of these schemas contains an EMPLOYEE table and one of the items in that table is the vacation usage of each employee.
The mediation flow takes a request message, which contains the employee identifier and department name. The flow then looks up the vacation usage details in the appropriate table, and returns the number of vacation days used and vacation days remaining for that employee. Because the employee tables are in different departmental schemas you can use a filter node to check the department value in the message and then route the message to a database lookup node appropriate to that schema, as shown in Figure 1.
Figure 1. Flow with separate database lookup mediation primitives
However, using this approach, if any new departments are created the mediation must be changed to add new filter conditions and database primitives, after which the mediation must be redeployed. A more flexible alternative is to create a single Database Lookup mediation primitive that has promoted its Table property. A preceding Policy Resolution mediation primitive can obtain the appropriate table name from a policy document, where the value is determined by the department field in the input message, as depicted in Figure 2.
Figure 2. Flow with policy resolution and single database lookup mediation primitive
If any new departments are created then the only changes required are a new policy attachment and gate condition, applied in WSRR.
Log a message depending on the target service
In this example, mediation flows are used to perform common processing on messages for two different target services. One is a test system and the other is a production system. Any messages that go to the production system must be logged for regulatory purposes, whereas messages bound for the test service do not need to be logged.
You can create a separate flow to deal with each target service. However, the same logic is then reproduced twice and any additional future target service requires a new separate flow to handle it. It is more flexible to use a service gateway pattern, which can accept messages from different clients and pass them on to different target services.
You can use an Endpoint Lookup mediation primitive within the service gateway to query WSRR and find the URL to which to route the client message. The target service information that is stored in WSRR can also have policies attached to it. In this example the Test target service has a policy that disables a downstream Message Logger mediation primitive. The Production target service has a policy that enables a downstream Message Logger mediation primitive, which ensures that all messages to the production target service are logged. See Figure 3.
If an additional service is added in the future (for example, a Development service), that service can be loaded into WSRR. You can attach an appropriate policy to the new target service.
For example, you can add a policy to disable logging. The Service Gateway mediation primitive can process messages for, and route messages to, the new target service without modification.
Figure 3. Flow with policy resolution
and optional logging
Mediation flow with mediation policy
Related concepts:
Mediation policy concepts
The mediation policy resolution process
Related tasks:
Applying policies using Business Space
Related information:
DeveloperWorks article: example of 'Module' scope policy resolutionDeveloperWorks article: example of 'Target Service' scope policy resolution