Entity relationships are the representation of relationships between various Dynamics CRM entities. The customization tools included with Dynamics CRM make it easy for system customizers to create new entities, modify existing entities, and create the relationships between them. Starting with Dynamics CRM 2015, hierarchical relationships are introduced standard to some entities. In addition, a visualization component allows you to graphically display the hierarchical relationships in both a tree structure as well as an entity-relationship diagram, as shown here:

Entity relationships define the association of one entity with other entities or with itself. For N:N relationships, a new relationship is represented as a new table relationship in the database.

The simplest example of an entity relationship is the creation of a lookup for an entity. This creates a one-to-many relationship between the two entities. This allows you to associate multiple child records with a parent...