Comparison of the Service Invoke mediation primitive and the Callout node

IBM BPM, V8.0.1, All platforms > Programming IBM BPM > Enterprise Service Bus programming > Invocation of Services > Service Invoke and Callout nodes
Comparison of the Service Invoke mediation primitive and the Callout node

You can call a service using either a Service Invoke mediation primitive or a Callout node. You must consider the similarities and differences between using either the Service Invoke mediation primitive and the Callout node.

Similarities between the Service Invoke mediation primitive and the Callout node:

The in terminal of the Service Invoke mediation primitive corresponds to the in terminal of the Callout node.
The out terminal of the Service Invoke mediation primitive corresponds to the out terminal of the Callout Response node.
The fail terminal of the Service Invoke mediation primitive corresponds to the fail terminal of the Callout Response node (for an unmodeled fault).
A modelled fault output terminal of the Service Invoke mediation primitive, corresponds to a modelled fault terminal of the Callout Fault node.
Differences between the Service Invoke mediation primitive and the Callout node:

The Service Invoke mediation primitive does not switch from request flow to response flow.
The Service Invoke mediation primitive does not modify either the transient context or the correlation context.
A Service Invoke mediation primitive has a separate timeout terminal. A Callout node only has a fail terminal.

Although, there is a functional similarity between the Service Invoke mediation primitive and the Callout node, the Service Invoke mediation primitive does not replace the Callout node. Consider the following when deciding whether to use the Service Invoke mediation primitive or the Callout node:

Considerations for using the Service Invoke mediation primitive or the Callout node
Use the Service Invoke if Use the Callout if
You need to call a service and return the response within a mediation flow. You need to mediate a message (without calling an intermediate service) and then call a service provider. The Callout provides the simplest model for this configuration.
You need to interact with multiple services, and produce an output that combines service responses.
You need to call an intermediate service.
For example, you might use an intermediate service to adjust a message, or validate a message externally. The mediation flow contains a Service Invoke mediation primitive, and a Callout node that is connected to the service provider.

Service Invoke and Callout nodes

Use the Service Invoke if	Use the Callout if
You need to call a service and return the response within a mediation flow.	You need to mediate a message (without calling an intermediate service) and then call a service provider. The Callout provides the simplest model for this configuration.
You need to interact with multiple services, and produce an output that combines service responses.
You need to call an intermediate service. For example, you might use an intermediate service to adjust a message, or validate a message externally. The mediation flow contains a Service Invoke mediation primitive, and a Callout node that is connected to the service provider.