Which Use Case model convention is used to insert another Use Case that defines an alternative path?

The <> relationship is the standard UML convention used to model optional behavior or alternative paths for a Use Case. The extending Use Case adds functionality to the base Use Case only when specific conditions are met at a designated "extension point." This allows the base Use Case to be complete on its own, while the <> relationship introduces a conditional flow that is not executed every time the base Use Case is performed. This directly corresponds to defining an alternative path.

A. Include: This relationship models mandatory, not alternative, functionality. The included Use Case's behavior is always part of the base Use Case's flow.

C. Exception: An exception is a type of alternative path (specifically for handling errors), but <> is the formal modeling convention used to represent this relationship in a diagram.

D. System: This refers to the system boundary, a rectangle in a Use Case diagram that delineates the scope of the system, not a relationship between Use Cases.

1. Object Management Group (OMG). (2017). OMG Unified Modeling Language (UML), Version 2.5.1.

Section 18.1.3.3 (Extend), Page 641: "An Extend is a relationship from an extending UseCase (the extension) to an extended UseCase (the extendedCase) that specifies how and when the behavior defined in the extending UseCase can be inserted into the behavior defined in the extended UseCase... The extension takes place at one or more specific extension points defined in the extended UseCase." This official specification defines extend for inserting conditional behavior.

2. Fowler, M. (2004). UML Distilled: A Brief Guide to the Standard Object Modeling Language (3rd ed.). Addison-Wesley.

Chapter 9, Use Case Diagrams, Page 102: Fowler explains the extend relationship as indicating "that one use case is an optional addition to another." He contrasts this with include, which is not optional. This supports extend as the correct choice for alternative paths.

3. Dennis, A., Wixom, B. H., & Tegarden, D. (2015). Systems Analysis and Design: An Object-Oriented Approach with UML (5th ed.). Wiley.

Chapter 5, Use-Case Modeling, Page 145: The text states, "The extend relationship represents the extension of the functionality of a use case to incorporate optional behavior... It is used when a use case adds steps to another, more basic use case." This directly aligns with the concept of an alternative path.