Decision Services
A decision service is the unit of execution of a DMN model. A single DMN model typically defines multiple decision services. On the Trisotech Automation platform, each decision service is exposed for execution as a REST service to any external client application or process, and can be executed as well by a BPMN business rule task or a CMMN decision task.
A decision service can be invoked by a decision in DMN as well. In that case, the decision service is represented in the DRD as a collapsed decision service shape linked to its invoking element by a knowledge requirement, similar to BKM invocation.
![invoke decision service](_images/invoke-decision-service.png)
Unlike a BKM, a decision service is defined not by a single value expression but by a DRD. The inputs and outputs of that service are best defined using the Decision Service Wizard on the DMN ribbon.
![decisionservicewizard 1200x395](_images/decisionservicewizard-1200x395.png)
Alternatively, they can be defined in a standalone DRD using the expanded decision service shape.
![expandeddecisionserviceshape 1200x791](_images/expandeddecisionserviceshape-1200x791.png)