Software Design and Architecture T.Y. Computer

Use Case Diagrams

• Use case diagrams illustrate system interactions, showing relationships between actors and use cases.
• Key components include actors, system boundary, use case specifications, and their relationships such as inclusion and extension.
• Important for modeling system context and requirements.

Use Case Modeling

• An essential part of requirements engineering, helping define system boundaries and functions.
• Involves identifying actors, finding use cases, and creating use case specifications and scenarios.

Importance of Requirements

• Incomplete requirements are the leading cause of project failures.
• Factors contributing to failures: lack of user involvement, unrealistic expectations, lack of planning, and changing requirements.

Definition of Requirements

• Requirements specify what needs to be implemented, including desired behaviors, properties, and constraints of the system.
• A software requirement specification (SRS) consists of functional and non-functional requirements alongside a use case model.

Understanding Use Cases

• Use cases describe the functional requirements of a system and were first introduced by Jacobson in 1987.
• They outline sequences of events initiated by actors that achieve meaningful system actions.
• Always start with primary actors; secondary actors may interact but do not initiate use cases.

Identifying Use Cases

• Begin with a list of actors and ask what functions they require from the system.
• Evaluate if the system needs to store/retrieve information or react to external events.

Key Concepts in Use Cases

• Define system boundaries and identify all actors, which can include humans, roles, and external systems.
• Use cases can be abstract or concrete, emphasizing different levels of detail or specific actions.

Actor Identification

• Actors are entities that interact directly with the system, helping establish system boundaries.
• Consider who uses the system, what roles they play, and how they interact with it.

Purpose of Use Cases

• Serve as a means to capture and validate requirements while involving users in the process.
• Assist in identifying design elements and facilitate project management, design iterations, and testing.

Distinction of Use Cases

• Use cases do not depict internal functionalities or capture non-functional requirements; they focus solely on external interactions and user goals.
• Not to be confused with single line messages or overview documents.

Characteristics of Use Cases

• They describe interactions to achieve specific goals using present tense and active voice.
• Should maintain an appropriate level of detail without assumptions about system implementation.

Use Case Specification

• Formatting includes use case name, unique identifier, brief description, involved actors, preconditions, main flows, postconditions, and any alternative flows.

Types of Use Cases

• Differentiate between business and system use cases based on their focus and application within projects.

When to Analyze Use Cases

• Use case analysis is conducted to understand system behaviors from various actor perspectives, ensuring comprehensive coverage of user interactions.