Capturing the Requirements as Use Cases

1. Requirements Description

• What need to describe

1. The artifacts created in the requirements workflow
2. The workers participating in the requirements workflow
3. The requirements capture workflow activities.

• Workers and artifacts involved
• System Analyst

1. Use-Case Model
2. Actor
3. Glossary

• Use-Case Specifier

1. Use Case

• User-Interface Designer

1. User-Interface Prototype

• Architect

0. Artifacts

1. Artifact: Use-Case Model

• The system's functional requirements
• The conditions or capabilities to which the system must conform
• Agreement between the customer and the developer
• Essential input for analysis, design, and testing

1. Artifact: Actor

• Actors represents parties outside the system that collaborate with the system.
• Actors correspond to workers and/or business actors in a business.
• An actor plays one role for each use case which it collaborates.
• An instance of an actor is a specific user interacting with the system.

1. Artifact: Use Case

• A use case represents each way the actors use the system
• A use case is a chunk of functionality that the system offers to add a result of value to its actors.
• A use case specifies a sequence of actions, including alternatives of the sequence, that the system can perform, interacting with actors of the system.
• Use-case instance
• A use case specifies the behavior of dynamic use-case instances or a scenario of use of the system.
• A use-case instance is the performance or execution of a use case.
• A use-case instance interacts with an actor instance.
• A use-case instance does not interact with another use-case instances
• Flow of Events
• For each use case
• It can be captured as a separate textual description of the use case's sequence of actions.
• It specifies
• what the system does when the use case is performed, and
• how the system interacts with the actors when the use case is performed.
• It describes a set of sequences of actions.
• Special Non-functional Requirements

1. Artifact: Architecture Description

• An architectural view of the use-case model.
• It depicts the architecturally significant use cases.
• An architecturally significant use case
• has some important and critical functionality, or
• involves some important requirement

that must be developed early in the software's life cycle.

• The architectural view is used as input when use cases are prioritized to be developed within an iteration.

1. Artifact: Glossary

• To define important and common terms used by analysts to describe the system
• Useful in reaching a consensus among developers
• Regarding the definitions of various concepts and notions, and
• Reducing the risk of misunderstandings
• It can be derived from a business or domain model
• It is more focused on the system to be built instead of the system's context.

1. Artifact: User-Interface Prototype

• Help understand and specify the interactions between human actors and the system.
• One user-interface prototype for each use case.

• A worker is a position in the unified development process to which a real person can be assigned.
• With each worker there is a description of the responsibilities and the expected behavior of that worker.

1. Worker: System Analyst

• The whole set of requirements that are modeled as use cases
• Delimiting the system
• Finding the actors and use cases
• Ensuring that the use-case model is consistent and complete.
• The modeling leader and coordinator

• Individual use cases

1. Worker: Use-Case Specifier

• Responsible for the detailed description of one or more of the use cases.
• Work closely with the real users of the use case that s/he is responsible.

1. Worker: User-Interface Designer

• visually shaping the user interface
• developing, for each actor, a user-interface prototype for some use cases

• Responsible for describing the architectural view of the use-case model.