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Object and class relationships

A class diagram shows the structure of a system through classes, attributes, operations, and relationships between classes. It includes classes and their properties like attributes and methods. It also shows relationships between classes like associations, aggregations, generalizations, and dependencies. The class diagram is a key tool in object-oriented analysis and design.

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2 A CLASS is a template (specification, blueprint) for a collection of objects that share a common set of attributes and operations. Health Club Member Class Objects attributes operations Defining Class
UML Class Diagrams 3 What is a Class Diagram? •A Class Diagram is a diagram describing the structure of a system shows the system's •classes •Attributes •operations (or methods), •Relationships among the classes.
4 1 of 2 UML Class Diagram Notation Class Member memberNumber firstName lastName telephone address city etc... checkOutVideo checkInVideo buyItem etc... attributes operations { { Expanded view of a Class into its three sections: Top: Class Name Middle: attributes Bottom: operations
5 2 of 2 Object Association n n Class Generalization Relationship Object Aggregation Association 0..* 1..* Object Composition Association 0..* 1 Will always be “1” UML Class Diagram Notation
UML Class Diagrams 6 Essential Elements of a UML Class Diagram Class Attributes Operations Relationships
7 Association Aggregation/Compostion Dependencies Generalization Realization
8 Associations An association between two classes describes connection among them. If the association is between two classes then it is called binary association. There can be association among more than two classes. It is represented by a solid line. Example: “An Employee works for a Company” Employee Company
9 Class A Class B role A role B Company Person Employer Employee Example: Associations
10 Aggregation & Composition •Aggregation (shared aggregation): • is a specialized form of ASSOCIATION in which a whole is related to its part(s). • is known as a “part of” or containment relationship and follows the “has a” heuristic • three ways to think about aggregations: • whole-parts • container-contents • group-members • Composition (composite aggregation): • is a stronger version of AGGREGATION • the “part(s)” may belong to only ONE whole • the part(s) are usually expected to “live” and “die” with the whole (“cascading delete”) • Aggregation vs. Composition vs. Association???
11 Aggregation Composition 0..* 1..* Faculty CourseTeaching 1..* 1 SalesOrder SalesOrderLineItem (another: hand --> finger)(another: assembly --> part) (team-teaching is possible)
12 Generalization • Deriving a class out of a parent class having some inherited property(from the parent class) and some new property of the derived class. • The term generalization is for the inheritance in the bottom to the up direction i.e. from derived class to the parent class.
• It is represented by a solid line with a large arrow head pointing towards the parent class. • Example: 13 Vehicle Car Truck
14 Dependency • A dependency relationship is a weaker form of relationship. A dependency states that a change in specification of one class may effect another class that uses first one but not vice versa. • It is represented by dashed lines. Dependent class Reference class
15 Realization • Realization is very similar to inheritance ,the only difference between them is a class is derived from an interface instead of a base class. • An interface is an abstract class. Interface class Derived class
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UML Class Diagrams 17
UML Class Diagrams 18