What is the difference between aggregation and composition in uml

Composition is a strong Association If the life of contained object totally depends on the container object, it is called strong association. Aggregation is a weak Association If the life of contained object doesn't depends on the container object, it is called weak association.

There is no single explanation. Different authors mean different things by aggregation. Most don't really mean anything specific by it. Composition mixture is a way to combine simple objects or data types into more complex ones. Compositions are a critical building block of many basic data structures. Aggregation collection differs from ordinary composition in that it does not imply ownership. Both denotes relationship between object and only differ in their strength. UML notations for different kind of dependency between two classes.

Composition : Since Engine is part-of Car, relationship between them is Composition. Here is how they are implemented between Java classes. Aggregation : Since Organization has Person as employees, relationship between them is Aggregation. Here is how they look like in terms of Java classes.

I always look at composition as 'needs a', i. So staying with the car analogy, my aggregation may be to represent a journey which may involve bringing a car and passengers together. The journey does not own the car or the passengers, I'm aggregating data that is related for a specific scenario. When the journey is completed the car and the passengers go on. When a car is ended, the car and it's engine are normally destroyed together. If I delete the first one, its contents vanish with it.

The second one, on the other hand can vanish without affecting its members existence unless there is a specific method that deletes each object as its pointer is deleted. The aggregation is when those subsets exists independently of the father set. As a monitor can be unplugged from the computer to be connected to another. The composition is when those subsets depends of the existence of the father set.

As a leaf is a part of a tree or liver is a part of a body. These concepts talks about the kind of dependency between two objects or classes, conceptually.

Directly in a program, in an aggregation, when the father object disposes, the aggregate objects should be disposed too. In the same scenario for a composition, composite son objects will persist then the father object dispenses. Sign up to join this community.

The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Aggregation vs Composition Ask Question. Asked 10 years, 7 months ago. Active 1 year, 11 months ago. Viewed k times. Improve this question. Add a comment.

Active Oldest Votes. Example 2: very simplified A Text Editor owns a Buffer composition. Himanshu shriv. Previous Page Print Page. Next Page. Dashboard Logout. In composition , parent entity owns child entity. In Aggregation , parent Has-A relationship with child entity. Actually, quite the opposite!

To sum it up association is a very generic term used to represent when one class used the functionalities provided by another class. We say it's a composition if one parent class object owns another child class object and that child class object cannot meaningfully exist without the parent class object. If it can then it is called Aggregation. Generalization is a mechanism for combining similar classes of objects into a single, more general class. Generalization identifies commonalities among a set of entities.

The commonality may be of attributes, behavior, or both. In other words, a superclass has the most general attributes, operations, and relationships that may be shared with subclasses. A subclass may have more specialized attributes and operations. Specialization is the reverse process of Generalization means creating new sub-classes from an existing class.

Generalization is the term that we use to denote abstraction of common properties into a base class in UML. When we implement Generalization in a programming language, it is often called Inheritance instead. Generalization and inheritance are the same.