What is defined as a relationship between two entity types?

A binary relationship is defined as a connection between two entity types in the context of database design and entity-relationship modeling. This type of relationship illustrates how two different entities interact with each other. For example, in a database that includes a "Customer" entity and an "Order" entity, a binary relationship could represent that a customer can place multiple orders, while each order is associated with exactly one customer.

In contrast to unary relationships, which involve a single entity type related to itself, and ternary relationships, which involve three different entity types interacting together, binary relationships focus specifically on the interaction between just two entities. Hierarchical relationships pertain more to a parent-child structure and are not classified in the same way as binary, unary, or ternary relationships. Understanding these distinctions is essential for effective database design and ensuring proper relationships among entities are established.