In your CRM module, you include the ability to create relationships between different entities.
Specifically, I can go to a Contact and create a relationship with a Customer. However, the Relations tab is not available in the Customer form so I can only see the relationship from the Contact side. The Business Account option is not available for relationships. However, if I go to the Business Account form I can see the relations tab and I can create a relationship between the Business Account and the Contact. When I view the relationship from Contact, it displays the related entity with the type of Customer (yet it was added from the Business Account).