Association (CDS)
What it is
A declared, navigable relationship between CDS entities (like a join you can follow by name) that the framework resolves lazily — only when the path is used. Compositions are a special, ownership-implying kind of association used by RAP for parent/child.
Why it matters for Clean Core
Associations are how CDS and RAP express the shape of a business object without eager joins. They make models readable and let OData navigation and RAP compositions work.
Common pitfall
Reaching for an explicit JOIN where an association reads cleaner and only materialises when consumed. And in RAP: confusing a plain association with a composition — the composition is what makes a child part of the BO.