Relationships connect objects to each other in the Repository. When you define a new relationship type, you also define an origin collection type and a destination collection type. The origin collection type connects the relationship type to one interface; the destination collection type connects the relationship type to a second interface. The classes that implement those interfaces are now "related" in your information model.
To create a new relationship type (and its corresponding pair of collection types) and attach it to two interfaces
Note One of the relationship types that you create for your information model must enable moving from the Repository’s root object to some objects of your information model. (See Information Model Creation Issues for more information about why you need this interface.)