Amazon.com: UML Distilled: A Brief Guide to the Standard Object Modeling Language (2nd Edition): Martin Fowler, Kendall Scott: B

Handy notes on project management:

This is paraphrased from the book UML Distilled 2nd Edition:
http://www.amazon.com/UML-Distilled-Standard-Modeling-Language/dp/020165...
Scenario: sequence of steps describing an interaction between a user
and a system. Usually in "narrative" or "essay" form no longer than a
paragraph.
Use Case: set of scenarios tied together by a common user goal. Use
cases are sometimes rendered as more formalized scenarios with
numbered steps and conditional branches and/or loops.
Use Cases are captured in Use Case Diagrams. In a use case diagram, a
use case is indicated by an oval, with the name of the use case inside
the oval.
Actors: An Actor is a "role" that a user plays in relation to the
system. Actors carry out use cases. An actor can perform multiple use
cases and multiple Actors can perform a use case. Actors are
signified by stick figures in use case diagrams. Actors aren't always
human, they can be any agent that interacts with a system, like
another system.
Use Case Relationships: In addition to relationships between Actors
and Use Cases, you can show relationships between use cases.
Relationships are indicated by arrows.
The "Include" relationship is used when you have similar behavior
across multiple use cases. This makes it possible to streamline
diagrams by "including" other use cases. Type <> under a
dotted relationship arrow to indicate an "include" relationship.
Use case "generalization" is used when you have one use case that is
similar to another but does more. This makes is possible to capture
variations or alternate scenarios. Generalizations are depicted by a
solid arrow with a hollow point.
The "extend" relationship is like a generalization with more rules. An
extending use case may add behavior to a base use case but the base
use case must specify "extension points." Extension points are
denoted under a line under the name of the use case in the use case
oval. Extensions are denoted by typing <> under a dotted
relationship line and listing the extension points the relationship
touches.
Rules of thumb:
Use "include" to avoid repetition.
Use "generalization" when describing a variation on normal behavior.
Use extend when describing a variation on normal behavior and you wish
to be more specific/formal, declaring extension points in the base use
case.