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UML Class Diagram

UML class diagrams methodology is been used extensively and especially in software design. It has many types of diagrams for the different software design purposes, we can present the basic diagram of UML in the SQL and compare them with the ER diagram. 

In the UML diagram class, which is similar to the entity type and which is displayed as a box which will include like: 

  • Top section will give class name
  • Middle section will include attributes for the individual objects of the class
  • Last section will include operations which will be applied to objects

Let us consider an example for the company concept:

UML Class Diagram
A UML diagram class

Attributes are like name, SSN, bdate, sex, etc. Here the designer will state the domain of the attributes if required by keeping the colon and followed by domain name or maybe description. A composite attribute will be designed as the structured domain. The relationship is also called the associations in the UML and the terminology and the relationship instances are known as links.

The binary association will be drawn as a line which is connecting the participation classes and it can have a name optionally and a relationship which is called a link attribute will be placed in the box that is been connected to the association line by the dashed line. And the notations which are explained in the diagram with constraints are called the multiplicities in the UML terminology and these will be specified in the form of min and max with an asterisk (*) notation.

In the UML diagram, a single asterisk represents multiplicity of 0..* and a single will represents 1..1 a recursive relationship.

In UML there will be two types of relationship: one is an association and the other is aggregation. Aggregation which will represent the relationship between the whole object and its component part has distinct diagrammatic notations. Aggregation, as well as an association, will not have different structural properties and the choice of which type of relationship to make use of will be subjective. UML will distinguish between unidirectional and bidirectional associations where the unidirectional line will be connecting the classes, will be displayed with an arrow which will indicate that only one direction for accessing the classes.

For example: suppose if we expect to access the manager of the department which starts from the department object, then we draw an arrow from the department to the employee. In this relationship, instances specified are ordered. Suppose if there is no arrow then the bidirectional case will be assumed which will be the default.

Weak entities will be redesigned using a construct which is called qualified association in the UML. This will be represented by identifying the relationship and the partial key which will be placed in the box and attached to the owner class. The operations which are given each of the classes will be derived from the functional requirements of the applications and generally which is to specify the names of the operation in the initial stage for logic operations which are expected to be applied to individual objects of the class.

As the designs are refined, more details will be added like exact arguments types for each of the operations. In addition to that, functional description of each of the operation details.


  1. What is uml? Explain briefly
  2. Draw UML diagram for school based concept
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