CPSC 3720 - DAY 15
FEBRUARY 20, 2017

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SEQUENCE DIAGRAMS
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	A sequence diagram ties use cases with objects.
		Shows how the behavior of a use case is distributed among obj.
	
	Not used to communicate with the user or customer
		Too technical

	Typically covers one scenario
		Can include conditional statements, but they can clutter up the
		diagram quickly
	
	You need at least one sequence diagram for each use text.

	CH 4 UML Distilled

	Sequence Diagrams

	At the top there are participants.
		Actors and objects
		Sometimes objects will have the name and the class

	Each Participant has a vertical lifeline
		Shows how long the object lives in the systems memory
		Rectangles on the line show that the object is actively
		processing something

	Participants send messages to other participants via an arrow from one 
	life line to another
		Messages are function calls (include parameters)
		Dashed arrows are returns
		First message is the found message
			Can come from an Actor, or no specific participant
		
	The horizontal level of the arrows show the temporal relationship

	Creation and deletion of objects

	One participant can create another participant by using the found msg
	"new" to show the instantiation of an object (or create)
		Similar to new when calling the constructor of an object
		The rectangle of the created participant is on the same horiz
		level as that message.

	A participant's life can end
		Shown with a large X and the life-line ending
		Can be done with a close command
		Can be self-deletion

	Loops and conditionals

		Not a strength of sequence diagrams, but not bad
			Activity diagrams are better though, or even just
			pseudo code
		Loops and conditionals use interaction frames
			Seperate part of the sequence diagram
		Each frame can have one or more fragments
			Fragments are used to show the seperate paths based on
			the condition
		Each fragment has a guard which shows the condition for
		entering that fragment
		Each frame has an operator in the top left corner to show what
		kind of operation it is.
	Heuristics
		
		First column should correspond to actor who initiated the use
		case
		Second column should be boundry object
		Third column should be control object
		Control object created by boundry object initiating the use
		case
		Entitiy objects accessed by control objects
		Entity objects never access boundry or control objects
			This makes it easier to share entity objects across
			use cases.