Serena Release Control is a hierarchical system, with Release Train as the highest level organizing entity, Application Release next, and so on. Release Packages can optionally participate in the hierarchy or exist standalone. Deployment Tasks are dependent on Release Packages, and Deployment Process Templates are standalone, although they populate the Deployment Process Templates and in that respect have a link to both Deployment Tasks and Release Packages.
Most of the default workflows allow editing and associating entities to other entities only when items are in the Development or Planning states. For example, you can associate application releases with a release train only when that release train is in the Planning state. You can associate release packages with an application release only when the application release is in the Development state.