olemus
UML: kahe üksteisest teadliku klassi vaheline side
= an association between two classes, both classes being aware of each other and their relationship with the other

ülevaateid
https://warrenlynch.gitbooks.io/uml/content/class-diagram/what-is-association.html
https://www.visual-paradigm.com/guide/uml-unified-modeling-language/uml-aggregation-vs-composition/