**Composition: Children can’t exist without parent. Aggregation: Children can exist separately from parent.** Aggregation and Composition are very similar. The difference has to do with **lifecycle** - that is, whether or not the children can possibly exist without the parent. Composition implies _when a parent is deleted, the children are also deleted_. Aggregation has no such implication. They still seem like they are used almost interchangeably in practice. From the source:  Interestingly - the UML 2.5 Specification doesn’t even define ‘Aggregation’. Like it’s not in there at all when you Ctrl+f ‘aggregation’. **** # More ## Source - [UML Association vs Aggregation vs Composition](https://www.visual-paradigm.com/guide/uml-unified-modeling-language/uml-aggregation-vs-composition/) ## Related - [[Entity Relationship Categories]] - [[UML]]