Issue computations are always executed as part of a workflow. There are two different styles of workflow. In the MPT, workflows are Java classes and manipulated as "pure code". Within the SPT, workflows are manipulated visually like a flow chart.
The following code sample shows an issue being raised programmatically in a workflow within the MPT.
Actions can be invoked anywhere within your application. As such you can raise issues in any class such as REST resources, IXM Engine tasks, etc.
Changes to the MPT require you to build and restart your server.