Aggregation

In aggregation, the relation between two entities is treated as a single entity. In aggregation, the higher-level relationship with its corresponding entities is aggregated into a higher-level entity.

For example, the Center entity offers the Course entity to act as a single entity in the relationship which is in relationship with another entity visitor. In the real world, if a visitor visits a coaching center then he will never inquire about the Course only or just about the Center instead he will ask inquiry about both.