Modeling interactions and behavior

1
Modeling interactions and behavior

• Lecturer Dr. Mai Fadel

2
Introduction

• An interaction model shows a set of actors and
  objects interacting by exchanging messages.
• A behavior model shows how an object or system
  changes state in reaction to series of events.

3
8.1 Interaction diagrams

• Interaction diagrams are used to model the
  dynamic aspects of a software system they help
  to visualize how the system runs.
• They show how a set of actors and objects
  communicate with each other to perform the steps
  of a use case or some other piece of
  functionality.
• Interaction diagrams can show several types of
  communication. e.g. messages exchanged over a
  network, simple procedure calls, and commands
  issued by an actor through the user interface.
  Collectively these are referred to as messages.
• The following elements can be found in an
  interaction diagram
• Instances of classes or actors use same symbols
  for objects and actors
• Messages shown as arrows. One of the objectives
  of interaction diagrams is to better understand
  the sequence of messages.

4
Sequence diagrams

• A sequence diagram shows the sequence of messages
  exchanged by the set of objects (and optionally
  an actor) performing a certain task.
• Object are arranged from left to right an actor
  that initiates the interaction is often shown on
  the left.
• Vertical dimension represents time.
• Lifeline is attached to each object or actor. It
  becomes an activation box during the period of
  time that the object is performing computations.
• The message is represented as an arrow between
  activation boxes of the sender and receiver.
  (label, argument list and response). Syntax
• Responsemessage(arg,)

5
Example the process of the registration of a
student in a course
6
Example the process of the registration of a
student in a course detailed level
7
Notes about the example

• The use of combined fragment marked opt.
• Combined fragment is a subsequent of interaction
  that is special in some way, and is shown in a
  box.
• The opt label means that it may or may not
  occur.
• A boolean condition, written in square brackets,
  describes the circumstances when it will occur.
• In this example, the condition is placed over the
  CourseSection lifline, and indicates that the
  subsequence in the combined fragment will only
  occur if the hasPrerequisite variable is true.

8
Representing loops in a combined fragment
9
Destroy symbol in sequence diagrams
10
Communication Diagrams

• A communication diagram shows several objects
  working together.
• It is very much like an object diagram except
  that it shows communication links instead of
  links of associations.
• It has much in common with sequence diagrams
• Message arrow with label, and a prefix number
  showing the order of the message
• Communication links can exist between two objects
  whenever it is possible for one object to send a
  message to the other one.

11
(No Transcript)
12
How to choose between using a sequence or a
communication diagram

• Sequence diagrams are often the better choice for
  the following situations
• You want the reader to be able to easily see the
  order in which the messages occur
• You want to build an interaction model from use
  case. (they already have a sequence of steps, SD
  shows the objects involved)
• You need to show the details of messages, such as
  parameters, and return values. (CD too much
  clutter)
• You need to show loops, optional sequences and
  other things that can only be properly expressed
  using combined fragments.
• Prefer CD when deriving interaction diagram from
  class diagrams. (CD are very similar to object
  diagrams)
• CD can be used to validate class diagrams
  suggest adding an association in order to make an
  interaction possible.

13
State diagrams

• Also known as state machine diagram
• It is another way of expressing dynamic
  information about a system
• At any given point in time, the system or object
  is said to be in a certain state. It remains in
  this state until an event occurs that causes it
  to change state.
• In each state, the system behaves in a different
  way.
• A transition represents a change of state in
  response to an event, and is considered to occur
  instantaneously that is it takes no time.
• Symbols in state diagrams rounded rectangles,
  arrows, labels on arrows, black circle, black
  circle with a ring around.
• A start state when a system starts running, it
  immediately takes a transition from the start
  state to a regular state. Only one start state
  and one unlabelled transition from it.
• End state when the system finishes its work when
  such a state is reached. More than one end state.

14
(No Transcript)
15
Elapsed-time transition
The event that trigger a transition can be a
certain amount of elapsed time.
after (30s)

• No end state

16
Transitions triggered by a condition becoming true
State diagram of a CourseSection class
17
Activities and actions in state diagrams

• You can present two kinds of computations using
  state diagrams activities and actions.
• Activity is something that occurs over a period
  of time while the system is in a state.
• The system may take a transition out of the state
  in response to completion of the activity.
• If some other transition is triggered first, then
  the system has to terminate the activity as it
  leaves the state
• It is shown textually by the word do/, followed
  by the description of what is to be done.

18
Activities and actions in state diagrams

• An action is something that takes place
  effectively instantaneously in any of the
  following situations
• When the system takes a particular transition.
• Upon entry to a particular state, no matter which
  transition causes entry.
• Upon exit from a particular state no matter which
  transition is being taken
• It should take place with no consumption of time
  gt simple, such as sending a message, starting a
  hardware device, or setting a variable.
• Syntax event/action, enter/action, exit/action.

Press button
ProposeSelection
19
State diagram for a garage door opener
Partial state diagram for a tape recorder