What is class diagram? How it is different from Object diagram? Draw class diagram for Online Examination System.

Ans. Class Diagram

 A class diagram is used to support functional requirement of system. In a static design view, the class diagram is used to model the vocabulary of the system, simple collaboration, and logical schema. It contains sets of classes, interfaces, collaborations, dependency, generalization and association relationship. The notation for classes and the relationship between classes is shown as:

Relationship among classes

If in any college, there are limited classrooms that have to be allocated to different classes and instructors are fixed for all classes, then the class diagram for the allocation of classrooms and instructors is shown as:

An object diagram shows a possible instantiation of a class diagram, typically representing a specially interesting scenario that you could create by instantiating the classes (and associations) in your class diagram.

An object diagrams shows a set of objects. For each object you show the type of the object (which again has to be one the classes in the class diagram), the values for the object attributes and links with other objects.

An object diagram is a snapshot of the objects in a system at a point in time. We can use an object diagram to show an example configuration of a snapshot from a class diagram.