METRICS FOR USE CASES: A SURVEY OF CURRENT PROPOSALS
Beatriz Bernárdez, Amador Durán, Marcela Genero · 2005
Extensions: extensions are branches of the main success scenario depending on a particular condition -the extension condition -in a given step.Some of these branches can lead to success while other can lead to failure of the use case.Cockburn recommends using extensions for handling both situations, while other authors like Leite et al. (2000) or Durán et al. (2002) use conditional steps for successful, usual branches and exceptions for branches triggered by exceptional conditions usually leading to use case failure. 4See Cockburn (2001), pages 93-95, for details about including a reasonable set of actions in a single step.