Layered builds

[Jeremy Mordkoff]

We are migrating from a single build pipeline to a pair of pipelines. The first will build our "platform" and then the second will build the application. This is because we will soon have multiple applications using the same platform. 

The applications should build if the platform changes OR if the application code changes. 

The application builds can be triggered by the usual source tree scanning logic in jenkins. But what is the best way to make sure that the application jobs all run wen the platform changes? Should I add a job build commands to the end of the platform pipeline to trigger all of the application builds? If I do this, is there a way to determine in the application builds that they were triggered by the platform build?