Use Case Diagram Tutorial
Each use case represents a unit of useful functionality that subjects provide to actors. An association between an actor and a use case indicates that the actor. A Use Case diagram captures Use Cases and relationships between Actors The following diagram illustrates some features of Use Case diagrams: Invokes and Precedes relationships are defined by the Open Modeling Language (OML). Products · Enterprise Architect · Eclipse Integration · Visual Studio Integration. This use case diagram relationships tutorial will cover all you need to Association between actor and use case; Generalization of an actor.
Important information is stored within the textual meta-content of the Use Cases or within diagrams behind, providing detailed information for each one. Use Cases may contain: This Use Case diagram shows two use cases and their associated actors. When read from top to bottom, these two use cases suggest a particular order, but in UML this is neither given nor intended.
The diagram merely describes what use cases there are and the involved parties. Process flow and order can be described textually within the scenario or later on within additional behavioral models by using activity, state or sequence diagrams.
Actors In a use case diagram, all parties stakeholders involved in a procedure are portrayed with the help of Actors. An Actor is defined as a role outside of the corresponding use case system, and which interacts with the system within the context of the use case.
Actors can be persons who use the system or external systems which access the system. They have demands and interests on the system, and are accordingly interested in the results. There can also be events which are triggered without the involved parties e. An Actor describes a role, which may be replaced by a discrete person or system when realized.
In special cases, when the role cannot be replaced by a discrete person or systemit has to be marked as Abstract to express that the actor is a generic role. Stereotypes may be used to categorize actors like sensors, timers, actuators, environmental influence, etc.
The following illustration shows different notations of an actor. UML provides the stick figure as the Actor symbol.
The role name of the actor is placed above or below the figure. It is possible to use any user-specific symbol. The block located to the right is the node symbol from the deployment diagram type.
The use of a block-type symbol or similar to indicate an external system is widespread, as a stick figure usually indicates a human user. Use Case A use case specifies a number of actions executed by a system and which lead to a result which is usually important to an actor or stakeholder.
Use cases are the activities which one names when describing a process. The following illustration shows various forms of notation of use cases.
The illustration on the left is standard notation. It is also possible to note the names of the use cases under the ellipse. The advantage here is that the size of the ellipse must no longer scale to the name of the use case. Interestingly, unlike actor notation, placing the name above the ellipse for use cases is not practiced in UML. System can be understood as the context of the use case in which the use cases of specific actions are executed. System can be a class or a component which represents the entire application.
The system is represented by one or more system frames boundaries ; Use cases — services and activities - to be performed by the system are shown in the system frame. To draw actors within a boundary will be incorrect!
Relationships are modeled with lines. Linking actors and use cases in this way means that both communicate with each other. An actor is linked to use cases using simple association. This indicates an interaction with the system belonging to the use case, and in the context of that use case. Relations can carry additional information, if needed. Without a writing, multiplicity will be On actors side a written multiplicity means the number of actors of the given role to be involved when interacting with the use case.
Without a writing, multiplicity on actors side will be It is not common for one to use navigable relations; however, these are allowed. These do not represent a specific direction of data flow — as they are usually interpreted — but rather indicate the initiator of the communication between actor and system.
Indicating a navigable association arrow to or from an Actoreven more semantics with a use case can be expressed. A directed association describes which part is the active and which is the passive. When an actor navigates to a use case, then the Actor is the active party and initiates the use case. Vice versa, in navigation from use case to actor, the actor is passive and will be required and requested by the use case to participate. The following example expresses that the Customer triggers the use case withdraw money, but once a time.
Use Case Diagram - UML 2 Diagrams - UML Modeling Tool
While the Bank-Server can be involved in any number of withdraw money use cases at the same time, the Customer can be involved only once at the same time.
Multiplicity describes the amount of possible instances, cardinality on the other hand a concrete amount. Use Case Relationships Use cases can also be reliant on one another With the "Include" relationship, a use case is bundled into and is a logical part of another use case. It represents a compulsory relationship and is therefore often referred to as "must-relationship". With the "Extend" relationship, however, one can also specify that a use case is to be extended under certain conditions and on another specific point the so-called extension point.
It represents an optional relationship and is therefore often referred to as "can-relationship". Use cases can also be generalized, whereby the general rules apply. Use cases can also be abstract italics and first be made clear via sub-use-cases specialized Use Cases.
Include Relationship A part of a use case which appears in the same identical form in other use cases may be transferred to its own use case and re-integrated universally via an Include relationship in order to avoid the redundant specification of these identical parts.
Unlike the Generalization relationship, when utilizing the Include relationship no characteristics are passed on.
Use Case Diagram Tutorial
The Include relationship is illustrated by a dashed arrow with open point in the direction of the use case to be included. The key word "include" is noted for the arrow. An actor must not necessarily be linked to the integrated use case.
Integrated use cases are often provided with the stereotype "secondary". This is not UML-Standard, but it is in common use since they are normal incomplete use case fragments and must be distinguished from the primary normal use cases. Example of "include" relationship Within a use case diagram an include relation specifies that the use case always uses the second one.
The timing of the usage is not expressed by the diagram itself, it may be described within the use case scenario or by a behavioral diagram describing this use case in detail.
Use case diagram
Please pay attention to include only use cases of the same specification level. Functionality needed several times should be modeled as use case once and can be used by others with relations any time needed. Extend Relationship If a part of the tasks are transferred from one circumstance to another, this is modeled in its own use case. The arrow is given the stereotype "extend". The Extend relationship points to the use case to be extended, and starts from that use case which describes the extension's behavior.
This has been defined by the inventors of UML, they preferred to have "extend" instead of "extended by". A use case can define any number of extension points. A use case diagram contains four main components Actor Actors are usually individuals involved with the system defined according to their roles. The actor can be a human or other external system. Use Case A use case describes how actors uses a system to accomplish a particular goal.
Use cases are typically initiated by a user to fulfill goals describing the activities and variants involved in attaining the goal. Relationship The relationships between and among the actors and the use cases.
SparxSystems Europe: Use Case Diagram
System Boundary The system boundary defines the system of interest in relation to the world around it. Benefits of Use Case Diagram Use cases is a powerful technique for the elicitation and documentation of black-box functional requirements.
Because, use cases are easy to understand and provide an excellent way for communicating with customers and users as they are written in natural language. Use cases can help manage the complexity of large projects by partitioning the problem into major user features i.
A use case scenario, often represented by a sequence diagram, involves the collaboration of multiple objects and classes, use cases help identify the messages operations and the information or data required - parameters that glue the objects and classes together.
Use cases provide a good basis to link between the verification of the higher-level models i. Use case driven approach provides an traceable links for project tracking in which the key development activities such as the use cases implemented, tested, and delivered fulfilling the goals and objectives from the user point of views. How to Draw a Use Case Diagram?
A Use Case model can be developed by following the steps below. Identify the Actors role of users of the system. For each category of users, identify all roles played by the users relevant to the system.
Identify what are the users required the system to be performed to achieve these goals. Create use cases for every goal.
Structure the use cases. Prioritize, review, estimate and validate the users. Draw packages for logical categorization of use cases into related subsystems.