Updated March 30, 2023
Difference Between Association vs Aggregation
The following article provides an outline for Association vs Aggregation. Association is defined as a relationship between two classes where one class use another class, refers to ‘Has-A’ relationship between two classes, aggregation and composition are subsets of association it means they are specific cases of association where the aggregation is a weak association, it means one object can exist without other and composition have a strong association of two objects where one object cannot exist without other objects, whereas, a whole and part of a relationship can be specified as a special type of association which is known as aggregation, it is a collection, i.e., a group of things that are stored together, also it implies a relationship where both objects can exist independently.
Head to Head Comparison Between Association vs Aggregation (Infographics)
Below are the top 10 differences between Association vs Aggregation:
Key Difference Between Association vs Aggregation
Let us discuss some of the major key differences between Association vs Aggregation:
- Type of Relationship: Association represents a has-a relationship, also having relation between two separate classes which establishes through their object that means it depends on the relationship. Association can be one-one, one-to-many, and many-to-many. For an example of the relationship between student and teacher. Multiple students can be associated with a single teacher and vice versa. Both can be created and deleted independently. Whereas aggregation is a group, body, or composition of many distinct parts or individuals, and it is a one-way relationship. It is a specialized form of association where all object has their lifecycle, but there is ownership and whole-part or a-part-of relationship that is represented by a diamond. The aggregation has a loose coupling between two objects, whereas the association is strongly coupled. For example, in the relation between department and teacher, a teacher may belong to multiple departments, but if we delete a department, that will not affect the teacher, or the teacher object will not destroy. So that, in aggregation, both objects can survive individually, which means that one object cannot affect the other object.
- Dependency: In Aggregation, it is implied that a relationship where a child can exist independently of the parent. For example, a car and driver have loose coupling between each of them that is aggregation because a car can exist without a driver and driver can exist without a car, the driver cannot forget his driving capability if he does not have a car, so it means that a car has a driver and a driver has a car, but they are not tightly coupled, so there is no dependency on each other, Whereas, association implies a relationship between two classes that describes some kind of activity, the association has a relationship between multiple objects. For example, consuming healthy food is not related to a healthy weight but to good skin, good hair, strength, and being active.
- Functionality: In object-oriented programming, an object communicates to the other object to use functionality and services provided by the object. Aggregation is a collection or gathering of things together; it is having a loose coupling between two objects or components. When an object contains a reference to another object, it has a Has-a relationship with the first object; then, it is called an aggregation. Aggregation helps to reuse the code. Aggregation is the process in which entities are combined to form a single meaningful entity. The specific entities are combined because they do not make sense on their own, and to establish a single entity, aggregation creates a relationship that combines those entities. The association defines the connection between two classes that are set up through their objects; we can also say that the association is the multiplicity between objects. Association allows an object to act on its behalf. Association also refers to the relationship between multiple objects and also defines how objects are related to each other and how they are using each other’s functionality where composition and aggregation are two types of association.
- Type of Association: In java, two types of association are possible the ‘IS-A association’ and the ‘HAS-A association’; the HAS-A association also has two types one is aggregation, and the other is composition. Composition and Aggregation are the two special forms of association. From A to B means that A uses B directly, and aggregation from A to B means that B is a part of A, but b can be shared, and if A is deleted, B is not deleted, it shows that how the “is part” is being implemented. An association declares that there can be a link between instances of the associated objects. For example, the association exists between classes when they use each other. In aggregation, both objects exist independently. Therefore, aggregation is a weak association.
Association vs Aggregation Comparison Table
Let’s discuss the top comparison between Association vs Aggregation:
| Sr. No | Association | Aggregation |
| 1 | Association is a relationship between two classes where one class uses the other class. | Aggregation describes a special type of association that specifies a whole and part relationship. |
| 2 | Association is not flexible. | Whereas aggregation is flexible. |
| 3 | Association indicates that there is also some kind of relation between the objects. | Aggregation implies a relationship where both objects can exist independently. |
| 4 | Association can be represented by a ‘has-a’ relationship. | Aggregation can be represented by a ‘has-a’ and whole-part relationship. |
| 5 | In association, the line segment is used between the components or the class. | Whereas in aggregation, diamond shape structure is used next to the assembly class. |
| 6 | The association is mostly based on relationships. | The aggregated relationship is a subclass of association. |
| 7 | Association is a Binary relationship. | Whereas aggregation is a unidirectional relationship. |
| 8 | In association, the objects in the class are strongly coupled. | Aggregation having a loose coupling between two objects. |
| 9 | In association, the code may not be reusable. | In aggregation, we can reuse the code. |
| 10 | In association, there is no ownership between two objects, and both have their lifecycle. | But in aggregation, there is ownership between two objects, and objects do not have their own. |
Conclusion
In the above article, it is concluded that the association is a relationship where all objects have their own life-cycle, and there is no owner and the object in aggregation have their own lifecycle, but there is ownership; child object cannot belong to another parent object and aggregation have loose coupling between two objects or components.
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