For instance, the rooms in a house cannot continue to exist if the house is destroyed. An aggregation is represented by a line from one class to another, with an unfilled diamond shape near the aggregate, or the element that represents the class that is assembled by combining the part elements.Īnother type of aggregation relationship, composition, is one in which the part elements cannot exist without the aggregate. The aggregate element relies on other elements as parts, but those other elements can also exist independently of it. For instance, a company has departments or a library has books. This type of association relationship indicates an element is formed by a collection of other elements. This can also be shown in a label on the line. MultiplicityĪn association relationship between elements can also have cardinality, for instance, one-to-one, one-to-many, many-to-one, or many-to-many, zero-to-many, and so on. In this case, the arrow loops back to the element. The basic way to represent association is with a line between the elements.Īssociation can be more complex, in that it can be directed, which is represented by an arrow showing the flow of control, or even reflexive, in cases where the element has a relationship to itself. The association indicates the nature and rules that govern the relationship. This simply means that one model element is linked in some way to another model element. They describe the behavior that is desired, or can be expected, between elements. Relationships add information to your diagram by clarifying the way that elements interact or depend upon each other. Relationships are also a type of model element. These are the shapes you draw to represent the components, or building blocks, of the system you are describing. Structure diagramsĪny UML diagram consists of model elements. UML diagrams divide neatly into two categories: structure diagrams and behavior diagrams. Let’s briefly list these before moving on to explore the various relationships possible in UML. UML 2 allows for fourteen different types of diagrams. As a visual language used to represent the structure and behavior of the system modeled, UML is extremely useful in a business environment where developers need to communicate their ideas to stakeholders with less programming knowledge. UML started out in the 1990s and it has gone through a number of iterations before arriving at the current version, UML 2. UML is a toolbox for creating such models and it incorporates a standardized system of notation and best practices suited to object-oriented design. Models assist developers by letting them initially work at a level of abstraction that helps them avoid pitfalls and optimize processes before programming. You can think of UML as a way to create blueprints so that software is fully understood by the designer before any coding begins. The Unified Modeling Language (UML) is a general-purpose modeling language used to visualize the design of a system.
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