Microsoft Dynamics CRM Online supports the following types of relationships between entities:
A hierarchical relationship allows each child record to store a reference to one parent record. A parent record can be referenced by an unlimited number of child records. The parent record can display all the child records in an associated view.
Hierarchical relationships provide opportunities to configure a number of behaviors that affect data integrity and the business rules in your organization. There are also limitations on the types of relationships that you can create. More information: Understanding Hierarchical Entity Relationships
- A 1:N Relationship is created or viewed from the primary entity. Any one record from the primary entity can be referenced by many records from the related entity.
A N:1 Relationship is created or viewed from the related entity. Many records from the related entity can reference any one record from the primary entity.
N:N (Many-to-Many) Relationships
N:N (Many-to-Many) relationships are not hierarchical because a record does not store a unique reference to another record. An N:N relationship allows reciprocally relating one or more records of an entity to a record of another entity. Also, an N:N relationship may be self-referential, meaning reciprocally relating one or more records of an entity to a record in the same entity.
Users who are associated with a security role that allows Read and Append privileges to one entity and Read, Write, and Append To privileges to another entity can relate records using this relationship.
Both hierarchical relationships and N:N relationships can be self-referential. This means that an entity can have a relationship with itself. This permits records to be directly associated with other records of the same type. For example, opportunities can be linked to related opportunities.
The only limitation to self-referential relationships is that records cannot be related to themselves in a parental relationship. This would create a circular reference.