use case diag

• each use case diagram represents a discrete task initiated by an actor (person OR other system)
• Use case is used to show possible interactions between users and system, systems interface features and subtasks, and different types of user (personas)
• system boundary is indicated with a box, interactions (associations) with lines, use cases with ovals, and relationships with dash arrow lines (arrow with hollow head = generalisation)

  
• dashed arrow can mean include or extend, identified by <<include>> or <<extend>> label. Include = action invokes sub-function (point to function) (eg. airline reservation includes subroutine to book seats). Extend = special version of a use case (points away from special case)(eg. order wine is special in comparison to order food as does not involve chef).