Week 11: Part 2
What is the purpose of logical views and some examples?
Used to model what a system is made up of and how the parts interact with each other. The types of UML diagrams that typically make up this view include class, object, state machine, and interaction diagrams.
What can be explained with a sequence diagram?
Using a sequence diagram, you can describe which interactions will be triggered when a particular use case is executed and in what order those interactions will occur. They illustrate the objects that participate in a use case and the messages that pass between them over time for one use case.
Definition of logical Views
Describes the abstract descriptions of a system's parts.
Definition of 'Black Hole' states
A black hole state is one that has transitions into it but none out.
Definition of 'Miracle' states
A miracle state is one that has transitions out of it but none into it.
Where are actors and objects placed in a sequence diagram?
Actors and objects that participate in the sequence are placed across the top of the diagram
Main Points of Sequence Diagrams
Dynamic model that shows the explicit sequence of messages passed between objects for a particular use case scenario. Time based ordering of the activity that takes place between a set of objects Aid understanding how the system works in real time.
Definition and purpose of Interaction Diagrams
Interaction diagrams model important runtime interactions between the parts that make up your system and form part of the logical view of your model. Communication and sequence diagrams
Purpose of a Activation Bar
It indicates that the sending participant is busy while it sends the message and the receiving participant is busy after the message has been received
How are messages specificed on a sequence diagram?
Messages on a sequence diagram are specified using an arrow from the participant that wants to pass the message, the Message Caller, to the participant that is to receive the message, the Message Receiver. When a message is passed to a participant, it triggers or invokes the receiving participant into doing something; and the receiving participant is said to be active. To show that a participant is active, an activation/execution occurrence bar is used.
Why is 'Time' important on a sequence diagram?
Time on a sequence diagram is all about ordering, not duration Time runs down the page on a sequence diagram in keeping with the participant lifeline. When objects continue to exist in the system after they are used in the sequence diagram, then the lifeline continues to the bottom of the diagram
What diagram is a member of interaction diagrams?
Sequence Diagrams pick this one when you prefer to see the order of the interactions as clearly as possible
Purpose of Sequence Diagrams
Sequence diagrams are all about capturing the order of interactions between parts of your system.
Definition of a temporary object?
Sometimes an object creates a temporary object; in this case an X is placed at the end of the lifeline at the point where the object is destroyed
Purpose of a 'Return Message'
The return message is an optional piece of notation that you can use at the end of an activation bar to show that the control flow of the activation returns to the participant that passed the original message.
Purpose of the 'Message Arrow'
The type of arrowhead that is on a message is also important when understanding what type of message is being passed. The order of messages goes from the top to the bottom of the page, so messages located higher on the diagram represent messages that occur earlier on in the sequence, versus the lower messages that occur later. Operation call messages passed between objects are shown using solid lines connecting two objects with an arrow on the line showing which way the message is being passed.
What are participants in a sequence diagram?
the parts that interact with each other during the sequence. Participants are always arranged horizontally with no two participants overlapping each other
