Processing Units (Engines) and Agent Classes are Configured in the CDD File
In the CDD, you configure processing units (equivalent to an engine at runtime). A processing unit references the agent or agents you want to include in the processing unit (engine) at runtime. At deploy time you specify which processing units to deploy.
In 3.x agents were configured using individual properties in the TRA files. Each TRA file provided the configuration for one engine.
Beginning with the 4.0.0 release, you configure all the processing units you need to deploy in a single CDD file. When you deploy an engine, you specify the processing unit to use. The processing unit configuration in the CDD determines which project resources and settings are used at runtime.
Some agents and processing units are created for you when you import a 3.x project into Studio based on 3.x information available. After you import the project into TIBCO BusinessEvents Studio, edit the CDD file to fully configure the agents and processing units as needed.