What is a Class Diagram in UML?
Class diagrams are easier than they look. They're simply diagrams that describe the structure of a system by modeling its classes, attributes, operations, and relationships between objects.
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What is a Class Diagram in UML?
The Unified Modeling Language can help you model various subsets of diagrams, including behavior diagrams, interaction diagrams, and structure diagrams. Class diagrams are a type of structure diagram, because they describe what must be present in the system being modeled. They are typically used by engineers to document software architecture.
A class diagram is the most basic component of object-oriented modeling. The class shape itself consists of a rectangle with three rows. The top row contains the name of the class, the middle row has the attributes of the class, and the bottom section expresses the methods or operations that the class may utilize. In a diagram, classes and subclasses are grouped together to show the static relationship between each object.
Class Diagram Applications
Class diagrams have a number of benefits for any organization. Try using them to:
- Illustrate data models for information systems.
- Understand the general overview of an application's schematics.
- Express the needs of a system and disseminate that information throughout the business.
- Create detailed charts that focus on the programming code needed to implement the described structure.
- Provide an implementation-independent description of types used in a system and passed between its components.
CLASS DIAGRAM COMPONENTS
Depending on the context, classes in a class diagram can represent the main objects, interactions in the application, and classes to be programmed.To answer the question of "What is a class diagram in UML?", you should first understand its basic makeup. Class diagrams model elements like the following ones—for a more detailed explanation, please see our class diagram guide.
- Classes - a template for creating objects and implementing behavior in a system. In UML, a class represents an object or a set of objects that share a common structure and behavior. They're represented with a rectangle that includes rows of the class name, its attributes, and its operations. When drawing a class diagram on a class diagram, only the top row must be filled out—the others are optional if you'd like to provide more detail.
- Name - the first row in a class shape.
- Attributes - the second row in a class shape. Each attribute of the class is displayed on a separate line.
- Methods - the third row in a class shape. Also known as operations, these are displayed in list format with each operation on its own line.
- Signals - symbols that represent one-way, asynchronous communications between active objects.
- Data types - classifiers that define data values. Data types can model both primitive types and enumerations.
- Packages - this containing shape is designed to organize related classifiers in a diagram. It is symbolized with a large tabbed rectangle shape.
- Interfaces - similar to a class, except that a class can have an instance of its type, and an interface must have at least one class to implement it.
- Enumerations - representations of user-defined data types. An enumeration includes groups of identifiers that represent values of the enumeration.
- Objects - instances of a class or classes. Objects can be added to a class diagram when representing either concrete or prototypical instances.
- Artifacts - model elements that represent the concrete entities in a software system, such as documents, databases, executable files, software components, and so on.
- Interactions - a term for the various relationships and links that can exist in class and object diagrams. Some of the most common interactions include:
- Inheritance - also known as generalization, this is the process of a child or sub-class taking on the functionality of a parent or superclass. It's symbolized by a straight connected line with a closed arrowhead pointing towards the superclass.
- Bidirectional association - the default relationship between two classes; both classes are aware of each other and their relationship with the other. This association is represented by a straight line between two classes.
- Unidirectional association - a slightly less common relationship between two classes; one class is aware of the other and interacts with it. Unidirectional association is modeled with a straight connecting line that points an open arrowhead from the knowing class to the known class.