Class diagram is a static representation used in the field of programming to describe the structure of a system, presenting its classes, attributes, operations and the relationships between the objects.
This type of representation is very useful in developing systems and softwares of computation, as it defines all the classes that the system needs to have and serves as a basis for the construction of other diagrams that define the type of communication, sequence and states of the systems.
The class diagram is the central part of the Unified Modeling Language (UML – Unfied Modeling Language). It represents the main purposes of the UML, having the function of separating the design elements from the system coding.
This language helps to model several subsets of diagrams, including behavior, interaction, and structure diagrams. It is typically used by engineers to document the architecture of softwares.
Class Diagram Components
The diagramming items that make up a class diagram can represent the classes that will be actually programmed, as well as the main objects or the interaction between classes and objects of the system. These items are:
Class
Abstract element representing a set of objects. It contains the specification of the object, its characteristics, attributes and methods.
Attribute
It defines class characteristics such as visibility, name, data type, multiplicity, initial value, and property.
THE visibility it can be public (represented by the + symbol) or private (represented by the - symbol). When it is public, other classes can have access to the attribute and when it is private, only the class itself has access.
It can also be protected (represented by the # symbol) or it can be packaged. (represented by the ~ symbol), where the attribute is accessed by the relationship of the class to the class external.
O Name is the attribute identification and the data type indicates the specification of the attribute data, as well as its initial value and yours properties, which depend on the language used in programming. THE multiplicity indicates the attribute's ability to make relationships with other classes.
Operation
It deals with the function required of an abstract object. This component also contains features such as name, visibility and parameters.
Association
This component deals with the ability of classes to relate. It can also contain the name, the multiplicity, and the navigation type, which indicate where the class information comes from and where it will go.
In terms of structure, the class diagram is presented in such a way that the shape of the class itself consists of a rectangle with three lines.
The top line contains the class name, the middle line, the class attributes, and the bottom line expresses the methods or operations the class can use. In a diagram, classes and subclasses are grouped together to show the static relationship between each object.
The figure below shows a example of a class diagram simple:
See also the meaning of software and Diagram.
