What relationship best describes the connection between an invoice and its items in UML?

The relationship that best describes the connection between an invoice and its items in UML is composition. In composition, there is a strong lifecycle dependency between the whole and its parts. This means that the items are inherently part of the invoice and cannot exist independently without it.

When we think about an invoice, its items are essentially a critical component of the invoice itself. If the invoice is deleted or ceases to exist, the items associated with it also lose their meaning and context. This is indicative of a composed relationship, highlighting that the items are tightly coupled to the invoice.

In a composition relationship, the whole (in this case, the invoice) controls the lifecycle of its parts (the items). The items cannot exist without being part of an invoice, reinforcing the idea of composition as the most accurate representation of this relationship.