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Excerpts from the UML Specification
about Use Case
1. UML V1.5 Specification GlossaryQuotes are directly from the noted UML Specification in black font color. [My comments are in blue font color like this sentence.]
use case [class]
The specification of a sequence of actions, including variants, that a system (or other entity) can perform, interacting with actors of the system.
[The perspective here is interesting. It assumes that the system performs and interacts with users. This is backwards. A system needs an event it recognizes to occur to do anything as defined below. A user produces events.]
[The term actor should be someone or something playing a role as we will see later.] 2. UML 2.1.1 Specification [UML 2.1.1 had no glossary - neatly avoids internal consistency problems with those pesky definitions! (v2.0 had a glossary)] Section 16.3.6 UseCase (from UseCases) – in Description
• A use case is the specification of a set of actions performed by a system, which yields an observable result that is, typically, of value for one or more actors or other stakeholders of the system.
[This excerpt is very close to the Building Requirements Consensus definition of use case.] • Each use case specifies a unit of useful functionality that the subject provides to its users, i.e., a specific way of interacting with the subject. This functionality, which is initiated by an actor, must always be completed for the use case to complete.
[The italicized excerpt is important when we discuss
exceptions
here.] 3. Jacobson in his book Object-Oriented Software Engineering7.2.3 Use CasesEach use case constitutes a complete course of events initiated by an actor and it specifies the interaction that takes place between an actor and the system.
[Note how Jacobson accurately describes that use cases are initiated outside the system – unlike the UML 1.5 definition of use case [class].]
[Jacobson did not separate the concepts of actors and roles. To him, actors were roles. See comment for excerpt
7.2.2 Actors in role excerpts
for details.]
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