The Composite is composed by declaring the parts it forms in the Composite Type interface declaration. Technically speaking, Composite Type is the only Fragment that is required to exist. The other Fragments are optional.
There are one very important thing to know about Fragments;
ONLY Mixins can maintain inter-method state.
That means that Concerns, Constraints and Side Effects can not assume that Java fields between method invocations are preserved. These Fragments must rely on either Mixins or external services for additional state.