We have already discussed Force.com is an object-oriented relational database management system. The backbone of the entire system based on Force.com is in relationships.
Relationships link two different objects with each other. For example, a library user can also be a library card holder. To represent this relationship we need to assign a customer record to a user record, this is achieved using a relationship.
There are two main types of relationships:
The Lookup relationship can be visualized in the following image: