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A use case is an example of how a user might interact with an application. To develop an application, one of the very first things that a developer must work with the customer to collect and analyze as many use cases as possible. It is from these use cases that a picture is built up that tells the developer how exactly the user (or any external entity) will interact with the system being built and thus how the sytem needs to be built.
Use cases are thus a technique for abstractly decomposing the initial problem as presented to the developer. Use cases enable one to bridge the divide between the colloquial, more natural descriptions of the problem as presented by the customer or user into the more concrete models needed by the developer. Use cases are important in understanding the relationships between the various processes that comprise the entire application under development.
Use cases give a high-level picture of the chain of processes that an application needs to perform in order to specific tasks. Generally, use cases start from the user desiring to do something, but can also be thought of in terms of either internal or external services that are offered. When viewed together, multiple use cases will become an graph of operations.
Use Case References:
A Use Case Diagram (a standard type of UML diagram) is used to visually represent a use case. Use case diagrams model the interactions between the tasks a system performs and external entities that need those tasks performed.
The main components of Use Case diagrams are the "actors", the users or other external entities, and the various components of the system being built. Arrows are used to indicate interactions between components.
(Note: Example diagram does not show all the features described below.)
<<extends>>" stereotype label for clarity. Extends stereotypes are useful for expressing optionally executed behavior where the performing of the specified extension determined by certain conditions being met or by whom is invoking the use case. Extensions can also be useful for describing command or strategy executions.
<<uses>>" or "
<<includes>>" stereotype label for clarity.
<<realizes>>" stereotype label for clarity.
REMEMBER: The (open) arrows between the individual uses cases in a use case diagram represent composition, not relative temporal execution!
When a use case has arrows (open arrowheads) pointing to other use cases, it means that use case is composed of the referenced use cases. It does NOT mean that one use case is executed and then the next is executed. If a temporal ordering of the use cases needs to be indicated, simply number the arrows to indicate the order in which the component use cases are executed in order to generate the overall use case. Convention is for the tasks to be ordered in temporal order from top to bottom in the diagram.
System block diagrams are the next developmental stage after creating Use Cases. These high-level modularizations of a system can be directly generated by simply organizing a well-constructed use case diagram.
For more information, see the Java Resources page on Use Case-driven System Block Diagrams.
Since use cases are fundamentally tied to the expression of and deliverance of the operations needed by users, use cases are a critical part of proving the viability of the design of a system's architecture.
End-to-end integration means that the system is operational to the point where a user-driven operation can be traced through its associated use cases from one end of the system to another end of the system. For instance, in a distributed system, the operation should traverse through the use cases in one system, cross the network into another system and then traverse throught the use cases on that remote system.
Early end-to-end integration is a crucial part of the development process to show that the proposed architecture of the system will work for the desired use cases. For this reason, customers often demand to see end-to-end integration of the system at very early stages of the development process.
Use case coverage refers to the ability to demostrate operationality of the system as traversals across all the use cases of the system. In order to show that a system has met its design requirements, the use case coverage must show that testing has demonstrated that all the use cases needed to meet the project requirements at that stage are operational. This is related to end-to-end integration in that use case coverage is essentially showing end-to-end integration through all the required use cases.
© 2020 by Stephen Wong