A class diagram is a statistic diagram that represents the static view of an app. It is used to construct an executable code, visualize different document aspects of a system, and describe a software code. A class diagram illustrates the structures of specific plans by showing their classes and their relationships among objects. The class diagram is divided into a set of classes and the relationship between those classes. The purpose of a class diagram is to design and analyze the static views of an app and describe a system's responsibilities.
An activity diagram is a behavioral diagram that is used to describe the dynamic aspects of a system. It shows how activities are coordinated to provide a specific service. It represents the series of control actions in a system similar to a data flow diagram of a flowchart. The activity diagram is used to describe the use case diagram. The activity diagram has many symbols, with the first symbol being the initial node, which is used to represent the starting point of activity, while the last symbol is the comment symbol, which adds comments to elements.
Object diagrams focus on specific attributes of objects and how the objects relate to each other. An object diagram is derived from the class diagram, and therefore it is dependent on the class diagram. The only difference between a class diagram and an object diagram is that the class diagram provides an abstract view of that object or system. Other than that, an object diagram carries the same purpose as the class diagram. The purpose of the object diagram is to get a static view of a system and perform forward and backward engineering.
A sequence diagram details how operations are carried out by capturing the interaction between the different objects in collaboration. Sequence diagrams show the order of interaction using the vertical axis because they are time-focused. It is used to capture the interaction between a system's user and the system or between the specific system and other systems. The purpose of the sequence diagram is to show the interaction between active objects in a system.