Class diagram - Wikipedia
In software engineering, a class diagram in the Unified Modeling Language ( UML) is a type of static structure diagram that describes the structure of a system by showing the system's classes, their attributes, operations (or methods), and the relationships among objects Association represents the static relationship shared among the objects of. Object Oriented DBMS. B Level DOEACC Module 3 OO Data Model- OO Relationships. no profile picture user. Post Object Oriented Data Model; 2. . Association A Sale class object may need to know all of the. Knowing and object-oriented language (such as Java) is a necessary but full use isn't realised without object oriented design. .. association relationship; composition is more specific . You might keep HTML pages in one folder, images in.
Here the student can exist without library, the relation between student and library is aggregation. Composition[ edit ] Two class diagrams. The diagram on top shows Composition between two classes: A Car has exactly one Carburetor, and a Carburetor has at most one Car Carburetors may exist as separate parts, detached from a specific car.
Association relationships in domain modeling class diagrams
The diagram on bottom shows Aggregation between two classes: A Pond has zero or more Ducks, and a Duck has at most one Pond at a time. The UML representation of a composition relationship shows composition as a filled diamond shape on the containing class end of the lines that connect contained class es to the containing class.
Differences between Composition and Aggregation[ edit ] Composition relationship 1. When attempting to represent real-world whole-part relationships, e. When the container is destroyed, the contents are also destroyed, e. When representing a software or database relationship, e.UML Class Diagrams - Association and Multiplicity
When the container is destroyed, the contents are usually not destroyed, e. Thus the aggregation relationship is often "catalog" containment to distinguish it from composition's "physical" containment. In practice, means that any instance of the subtype is also an instance of the superclass. An exemplary tree of generalizations of this form is found in biological classification: The relationship is most easily understood by the phrase 'an A is a B' a human is a mammal, a mammal is an animal.
The UML graphical representation of a Generalization is a hollow triangle shape on the superclass end of the line or tree of lines that connects it to one or more subtypes.
Relations between Classes
The generalization relationship is also known as the inheritance or "is a" relationship. The superclass base class in the generalization relationship is also known as the "parent", superclass, base class, or base type.
The subtype in the specialization relationship is also known as the "child", subclass, derived class, derived type, inheriting class, or inheriting type. Note that this relationship bears no resemblance to the biological parent—child relationship: The Wheel instance won't continue living without the Car instance containing it.
Is this a reasonable differentiation? Yes, that is a reasonable definition.
Just remember that others may not share that definition and that you might need to explain your use of aggregation to them. The definition I'm using? The 'has a collection of' definition? Association and composition are fairly straightforward. Aggregation is the wobbly one.
In practice, I find that the 'part of' test is works well 'ownership' is a sub-optimal way to think about it.
A person can be part of a club, thus a club aggregates people it does not own them. Example Let us consider two classes, Circle and Square, each with a method findArea.
Though the name and purpose of the methods in the classes are same, the internal implementation, i. When an object of class Circle invokes its findArea method, the operation finds the area of the circle without any conflict with the findArea method of the Square class. Generalization and Specialization Generalization and specialization represent a hierarchy of relationships between classes, where subclasses inherit from super-classes.
Generalization In the generalization process, the common characteristics of classes are combined to form a class in a higher level of hierarchy, i. Specialization Specialization is the reverse process of generalization.
Here, the distinguishing features of groups of objects are used to form specialized classes from existing classes. It can be said that the subclasses are the specialized versions of the super-class. The following figure shows an example of generalization and specialization. Links and Association Link A link represents a connection through which an object collaborates with other objects. Through a link, one object may invoke the methods or navigate through another object.
A link depicts the relationship between two or more objects. Association Association is a group of links having common structure and common behavior. Association depicts the relationship between objects of one or more classes.
A link can be defined as an instance of an association. Degree of an Association Degree of an association denotes the number of classes involved in a connection. Degree may be unary, binary, or ternary.
A unary relationship connects objects of the same class. A binary relationship connects objects of two classes. A ternary relationship connects objects of three or more classes.
Cardinality Ratios of Associations Cardinality of a binary association denotes the number of instances participating in an association.
Aggregation or Composition Aggregation or composition is a relationship among classes by which a class can be made up of any combination of objects of other classes.