7.1. Single-valued entity associations

Let's start with one-to-one entity associations.

We argued in chapter 4 that the relationships between User and Address (the user has a billingAddress, homeAddress, and shippingAddress) are best represented with a <component> mapping. This is usually the simplest way to represent one-to-one relationships, because the lifecycle is almost always dependent in such a case, it's either an aggregation or a composition in UML.