RMP Resource - Use Case

In the Unified Modeling Language (UML), use case diagram is a set of scenarios that describing and interaction between a user and a system. Use cases are used during the analysis phase of a project to identify and partition system functionality. The Use Case diagram is used to identify the primary elements and processes that form the system. The primary elements are termed as "actors" and the processes are called "use cases". It captures the functional aspects of a system. It displays the relationship among actors and use cases. It describes a sequence of actions that provide something of measurable value to an actor and is drawn as a horizontal ellipse.

This type of diagrams are used in almost every project, because they are helpful in exposing requirements and planning the project. In the drawing of use case diagram, connect the actors with the use cases with which they are involved, if an actor supplies information, initiates the use case, or receives any information as a result of the use case, then there should be an association between them.

There are two main components of a use case diagram:

Actor

An actor is a person, organization, or external system that plays a role in one or more interactions with the system. It interact with use case, for example, for modeling a banking application, a customer entity represents an actor in the application.To identify an actor, search in the problem statement for business terms that portray roles in the system. An actor is shown as a stick figure in a use case diagram depicted as shown

Use Case

Use cases describe the behavior of the system when the actors sends one particular stimulus. A use case is shown as an ellipse in a use case diagram as shown:

Associations

Associations between actors and use cases are indicated in use case diagrams by solid lines. It exists whenever an actor is involved with an interaction described by a use case. They are modeled as lines connecting use cases and actors to one another, with an optional arrowhead on one end of the line, that is often used to indicating the direction of the initial invocation of the relationship or to indicate the primary actor within the use case.

System boundary

A rectangle is drawn around the use cases, called the system boundary box, that indicates the scope of system. Anything within the box represents functionality that is in scope and anything outside the box is not. A system can not have infinite functionality, the system boundary defines the limits of the system. It shows as:

Example of Use Case Diagram

This diagram can easily be expanded until a complete description of the ordering system is derived capturing all of the requirements that the system will need to perform. Use cases are powerful tools for analysts to use when partitioning the functionality of a system.

Use case relationships and the corresponding diagrams help analysts to structure use cases such that their textual descriptions contain a minimum of redundant information; thus making the whole text document much easier to maintain. But use cases are not design tools. They do not specify the structure of the eventual software, nor do they imply the existence of any classes or objects. They are purely functional descriptions written in a formalism that is completely separate from software design.