A use case diagram of 9 diagrams in UML

In the UML 9 kinds of diagram, the use case diagram is the more important one kind of diagram, it is the diagram which produces in the system analysis stage, from the function carries on the analysis to the system the model, has played the strategically advantageous position function to the subsequent system development, the use case picture is good, then the system also is not far away from the success.

A dynamic view of the system's functions, composed of participants, use cases, and their relationships, is called a use case diagram. Use case diagram is the product of demand analysis, from the end of the first step of software requirements analysis, describe the functional requirements of the system, show the system users and users want to achieve the function, but also the developers and users of the system needs to communicate an effective means. Here is a detailed description of each:

Participants represent a set of abstractions that exist outside the system and interact directly with the system, the external entities of the system, subsystem, or class, and do not focus on people when looking for participants, and comprehensively analyze the parts associated with the system. In addition, when analyzing the use cases of the system, we must define the boundary of the system, and clearly divide the target system and the external system to create a good system development and running environment.

A use case is a system service or functional unit that a participant can perceive, defines how the system is used by the participant, and is a class that describes the main features of the system's functions. The greatest advantage of use cases is that the function of the target system is described from the outside from the perspective of the user, and the visible behavior of the whole system to external users is expressed. This is very important for the functional analysis and practice of the target system, so the analysis of use cases is also the focus here, starting from the analysis system participants, according to the participants to determine the system's use cases, but also through a number of issues unrelated to the participants to identify use cases, to ensure the integrity and rationality of use cases. In the analysis of use cases also consider the granularity of use cases, the use of large or small size of the case will cause the complexity of the system increases, not conducive to the implementation of the target system. After full analysis, the appropriate system functions to form the appropriate use case granularity, the effective division of the target system, is conducive to the further analysis of the system.

The relationships in a use case diagram are: The relationship between the actor and the actor, the relationship between the actor and the use case, and the relationship between the use case and the use case. These three relationships are the primary relationships in a use case diagram, where the actor and the actor are primarily generalized, or are referred to as inheritance relationships. A generalization relationship represents a general/special relationship between participants, such as the relationship between staff and managers in the sales system, the general operation of the staff for sales, and the general operation of sales and the management of sales, in which the staff has the function of a common part, so the staff is the general Class (super Class) , the manager is the special class, realizes the generalization relation from the clerk to the manager.

The relationship between a use case and an actor is an association, also known as a communication association. is a one-to-two relationship that indicates which participant communicates with which use case, and the arrow in the relational relationship in rational rose points to the use case,

the inclusion, extension, and generalization relationships can be abstracted between use cases and use cases. A containment relationship is a use case that can simply contain the behavior of another use case and use the behavior of the case it contains as part of its behavior. The extended relationship is to add the new behavior to the existing use case under certain conditions, and the new use case becomes the extension use case. The contrast between the two can be easily understood: the included use cases are necessarily executed after the underlying use case is executed, and the extension use cases are not necessarily executed after the underlying use case is executed, and can be selected for execution or not. For example, when the information in the database is modified, the use case of saving the information is bound to be executed, and in this use case, the use case of retrieving the password is extended: The user's password cannot be forgotten and the password will not be retrieved. The contrast between the two can be understood. There is also a generalization relationship between use cases, and a parent use case is special to form multiple child use cases. For example, shopping can be generalized to shopping on the streets and online shopping. The relationship between use cases facilitates the reuse of common behaviors in multiple use cases.  

In this part, the analysis of the use case diagram is the key to grasp. In the face of a strange system, how can we achieve a clear context? From the use case analysis, there is a purpose to partition the system, so that layers of analysis down, to clarify the system of ideas, unfamiliar system is not very unfamiliar. especially in the analysis of function, the analysis of this part is very important for the later system realization.

Use case diagrams for 9 diagrams in UML