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This article mainly shows you "what is the relationship between UML use case diagrams". The content is simple and clear. I hope it can help you solve your doubts. Let me lead you to study and learn this article "what is the relationship between UML use case diagrams".

UML use case diagram relationship

It is mainly used to illustrate the main event flow of the system, and it is mainly used to describe the needs of customers, that is, the actions that users want the system to have to complete certain functions, and generally understand that the use case is the functional module of the software. therefore, it is the starting point of the design system analysis stage, designers create and interpret use case diagrams according to customer requirements, which are used to describe which functional modules the software should have and the calling relationship between these modules. The use case diagram contains use cases and actors, and the use cases are connected by associations to reflect the entire structure and function of the system to non-technical personnel (usually users of the software), corresponding to the structure and function decomposition of the software.

A use case is a behavior visible from outside the system, which is a complete service provided by the system to one or more Actor. In principle, use cases are independent and juxtaposed, and there is no inclusion dependency between them. However, in order to reflect the business relationships between some use cases and improve maintainability and consistency, use cases can be abstracted into include, extend and generalization relationships.

Commonality: all extract the common part of the information from the existing use case as a separate use case, and then reuse the common use case in different ways to reduce the workload of model maintenance.

1. Include (include)

Inclusion relationships: use Inclusion use cases to encapsulate a set of similar actions (behavior fragments) across multiple use cases so that multiple Base use cases can be reused. The base use case controls the relationship with the containing use case, and whether the event flow containing the use case is inserted into the event flow of the base use case. The base use case can rely on the results that contain the execution of the use case, but neither side can access the other's properties.

The typical application of including relationships in UML use case diagrams is reuse, which is referred to as scenarios in the definition. But sometimes when the event flow of a use case is too complex, in order to simplify the description of the use case, we can abstract a certain event flow into an included use case; on the contrary, when the use case division is too detailed, we can also abstract a base use case. to contain these fine-grained use cases. This situation is similar to encapsulating an algorithm of a program into a subprocedure in a process design language, and then calling the subprocedure from the main program.

For example, in the business, there is always the ability to maintain so-and-so information, and if you use it as a use case, then new, editing, and modification will be described in the use case detail, which is too complex; if it is divided into new use cases, editing use cases, and deleting use cases, the division is too detailed. The inclusion relationship can be used to sort out the relationship at this time.

2. Expand (extend)

Extension relationship: a relatively independent and optional action in the base use case is encapsulated with an Extension use case in the UML use case diagram relationship, and then it is extended from the extension point (ExtensionPoint) declared in the base use case, thus making the base use routine more concise and focused. The extension use case adds a new behavior to the base use case. The extension use case can access the properties of the base use case, so it can determine whether or not to execute itself based on the current state of the extension point in the base use case. But the extension use case is not visible to the base use case.

For an extension use case, there can be several extension points on the base use case.

For example, the system allows users to export and print the results of the query. For the query, can export, print the query is the same, export, print is not visible. Import, print, and query are relatively independent, and new behaviors are added to the query. Therefore, an extended relationship can be used to describe:

3. Generalization (generalization)

Generalization relationships: the child use case is similar to the parent use case, but shows more specific behavior; the child use case inherits all the structures, behaviors, and relationships of the parent use case. The child use case can use a segment of the behavior of the parent use case, or it can be overloaded. Parent use cases are usually abstract. Generalization relationships in UML use case diagrams are rarely used in practical applications, and special behaviors in child use cases can be used as alternative flows in parent use cases.

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