Glossary writers generally try to produce a single, complete, consistent, and universally-acceptable set of definitions of terms for their books' domains. In the case of scenarios, this isn't possible as key terms are frequently used in different ways. Indeed, one of the aims of this book is to explore the range of uses of scenarios, and that inevitably means that the word has multiple meanings. So, instead, this glossary tries to point out where words are slippery, where they overlap, and how they are typically used—with synonyms and examples where necessary. Defined terms are indicated in Boldface.

Actor: UML term for Role. Note that officially the term does not imply either human agency or an individual agent. Human Actors are Operators. ‘Role’ is preferable to ‘Actor’ for discussions with Stakeholders.

Agile Methods: Software development approaches that emphasise user involvement and rapid iteration. See also User Story.

Alternative Course (Path, Scenario, Branch): Sequence of Steps that branches off from a Normal Course in a Use Case; typically represents the handling of an Exception. Note that ‘Alternative’ is ambiguous, meaning either Exception or Variation.

Alternative World: (= Situation, Snapshot) A Scenario that describes a more or less static picture of an imagined future situation, often parameterised in a Simulation model to explore and compare system options.

Atomic: (Something, e.g. a requirement) that cannot be cut up or sub-divided.

Black-Box Test: A ...

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