uml
In a UML class diagram, what is the difference between an association relationship and a dependency relationship?
From what I know, an association is a stronger relationship than a dependency, but I'm not sure how it is stronger.
Any example would be more than welcome 🙂
For two objects, Foo and Bar the relationships can be defined
Association - I have a relationship with an object. Foo uses Bar
public class Foo {
void Baz(Bar bar) {
}
};
Composition - I own an object and I am responsible for its lifetime. When Foo dies, so does Bar
public class Foo {
private Bar bar = new Bar();
}
Aggregation - I have an object which I've borrowed from someone else. When Foo dies, Bar may live on.
public class Foo {
private Bar bar;
Foo(Bar bar) {
this.bar = bar;
}
}
Here's some explanations from the Visual Studio 2015 docs:
UML Class Diagrams: Reference: https://docs.microsoft.com/en-us/previous-versions/visualstudio/visual-studio-2015/modeling/uml-class-diagrams-reference
5: Association: A relationship between the members of two classifiers.
5a: Aggregation: An association representing a shared ownership relationship. The Aggregation property of the owner role is set to Shared.
5b: Composition: An association representing a whole-part relationship. The Aggregation property of the owner role is set to Composite.
9: Generalization: The specific classifier inherits part of its definition from the general classifier. The general classifier is at the arrow end of the connector. Attributes, associations, and operations are inherited by the specific classifier. Use the Inheritance tool to create a generalization between two classifiers.
13: Import: A relationship between packages, indicating that one package includes all the definitions of another.
14: Dependency: The definition or implementation of the dependent classifier might change if the classifier at the arrowhead end is changed.
15: Realization: The class implements the operations and attributes defined by the interface. Use the Inheritance tool to create a realization between a class and an interface.
16: Realization: An alternative presentation of the same relationship. The label on the lollipop symbol identifies the interface.
UML Class Diagrams: Guidelines: http://msdn.microsoft.com/library/dd409416%28VS.140%29.aspx
Properties of an Association
Aggregation: This appears as a diamond shape at one end of the connector. You can use it to indicate that instances at the aggregating role own or contain instances of the other.
Is Navigable: If true for only one role, an arrow appears in the navigable direction. You can use this to indicate navigability of links and database relations in the software.
Generalization: Generalization means that the specializing or derived type inherits attributes, operations, and associations of the general or base type. The general type appears at the arrowhead end of the relationship.
Realization: Realization means that a class implements the attributes and operations specified by the interface. The interface is at the arrow end of the connector.
Let me know if you have more questions.
Best Answer
An association almost always implies that one object has the other object as a field/property/attribute (terminology differs).
A dependency typically (but not always) implies that an object accepts another object as a method parameter, instantiates, or uses another object. A dependency is very much implied by an association.