Duck can exist separately from a Pond, e.g. 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). Carburetors cannot exist as separate parts, detached from a specific car. The diagram on top shows Composition between two classes: A Car has exactly one Carburetor, and a Carburetor is a part of one Car. The aggregate is semantically an extended object that is treated as a unit in many operations, although physically it is made of several lesser objects. In UML, it is graphically represented as a hollow diamond shape on the containing class with a single line that connects it to the contained class. The contents of the container still exist when the container is destroyed. Īggregation can occur when a class is a collection or container of other classes, but the contained classes do not have a strong lifecycle dependency on the container. Furthermore, there is hardly a difference between aggregations and associations during implementation, and the diagram may skip aggregation relations altogether. However, an aggregation may not involve more than two classes it must be a binary association. As a type of association, an aggregation can be named and have the same adornments that an association can. As shown in the image, a Professor 'has a' class to teach. It is an association that represents a part-whole or part-of relationship. Here, a Professor 'has a' class to teach.Īggregation is a variant of the "has a" association relationship aggregation is more specific than association. Otherwise, instance scope is assumed by default.Ĭlass diagram showing Aggregation between two classes. To indicate a classifier scope for a member, its name must be underlined. Method invocation does not affect the classifier’s state.Attribute values are equal for all instances.Class members are commonly recognized as “static” in many programming languages.Method invocation may affect the instance’s state (i.e.Attribute values may vary between instances.Instance members are scoped to a specific instance.The UML specifies two types of scope for members: instance and class, and the latter is represented by underlined names. any attribute or method), these notations must be placed before the members' name: +Ī derived property is a property whose value (or values) is produced or computed from other information, for example, by using values of other properties.Ī derived property is shown with its name preceded by a forward slash '/'. To specify the visibility of a class member (i.e. UML provides mechanisms to represent class members, such as attributes and methods, and additional information about them like constructors. 2.1.5 Differences between Composition and Aggregation.They are also left-aligned and the first letter is lowercase. The bottom compartment contains the operations the class can execute.They are left-aligned and the first letter is lowercase. The middle compartment contains the attributes of the class.It is printed in bold and centered, and the first letter is capitalized. The top compartment contains the name of the class.In the diagram, classes are represented with boxes that contain three compartments: The classes in a class diagram represent both the main elements, interactions in the application, and the classes to be programmed. Class diagrams can also be used for data modeling. It is used for general conceptual modeling of the structure of the application, and for detailed modeling, translating the models into programming code. The class diagram is the main building block of object-oriented modeling. #University management system uml class diagram softwareIn 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. The individual classes are represented just with one compartment, but they often contain up to three compartments. Hierarchy of UML 2.5 Diagrams, shown as a class diagram.
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