ResourceGroups are mandatory in ERN
In ERN-3, all resources that are part of a release are referenced from the relevant
Release composite in its
ReleaseResourceReferenceList. This list is, however, only a "bill of material". It does not describe the order in which the resources are used to make up the release. This data is contained in the
ResourceGroup. To ensure this is the case, it is mandatory to include descriptions of all resources into the
ResourceGroup, together with the indicator communicating whether a resource is "primary" or a "secondary".
Therefore, the answer to the question is “yes” for ERN-3. This includes simple releases, such as singles.
For ERN-4 the situation is somewhat simpler. This is because ERN-4 does not have a
ReleaseResourceReferenceList. As a consequence, the
ResourceGroup is the only means, in ERN-4, by which the resources that make up the release can be listed and described. This composite also contains data which describes how the listed resources make up the release.