Chapter 6 Behavioural Models
Behavioral models describe the internal dynamic aspects of an information system that supports
the business process in an organization
Two types of behavioral models
First, there are behavioral models that are used to represent the underlying details of a business
process portrayed by a use case model.
Second, there is a behavioral model that is used to represent the changes that occur in the
When an analyst is attempting to understand the underlying domain of a problem, he or she
must consider both structural and behavioral aspects of the problem.
By viewing the problem domain as a set of use cases that are supported by a set of collaborating
objects, object oriented approaches allow the analyst to minimize the semantic gap between
the real world set of objects and the evolving object-oriented model of the problem.
The modeling focus on the class diagram is at the class level,, while the interaction diagrams
focus on the object level.
Objects, operations, and messages
Each object has attributes that describe information about the object, such as the patient’s
name, birth date, address, and phone number.
Each object has behaviors.
The behaviors are described by operations.
An operations, is nothing more than an action that an object can perform/
Each object can send and receive messages; messages are information sent to objects to tell an
object to execute one of its behaviors.
Two types of interaction diagrams.
They illustrate the objects that participate in a use case and the messages that pass between
The sequence diagram can be a generic sequence diagram that shows all the possible scenarios.
Instance diagrams, each of which depicts a single scenario within the use case.
1 Chapter 6 Behavioural Models
Elements of sequence diagram
Actors and objects that participate in the sequence are placed across the top of the diagram
using actor symbols.
A dotted line runs vertically below each actor and object to denote the lifetime of the
actors/objects over time.
Temporary objects, and in this case an X is placed at the end of the lifeline.
A thin rectangular box, called the execution occurrence, is overlaid onto the lifeline to show
when the class are sending and receiving messages.
A message is a communication between objects.
Operation call messages pass between classes are shown using solid lines connecting two
objects with an arrow on the line showing which way the message is being passed.
A return message is depicted as a dashed line with an arrow on the end of the line portraying
the direction of the return.
At times a message is sent only if a condition is met.
Building a sequence diagram
A six step process used to create a sequence diagram.
The first step in the process is to determine the context of the sequence diagram.
The second step is to identify the objects that participate in the sequence being modeled.
The third step is to set the lifeline for each object, to do this; you need to draw a vertical dotted
line below each class to represent the class’s existence during the sequence.
The fourth step is to add the messages to the diagram; this is done by drawing arrows to
represent the messages being passed from object to object.
The fifth step is to place the execution occurrence on each object’s lifeline by drawing a narrow
rectangle box over top the lifelines to represent when the classes are sending and receiving
The sixth step is to validate the sequence diagram.
Essentially provide a view of the dynamic aspects of an object-oriented system.
Essentially an object diagram that shows message passing relationships, instead of aggregation
or generalization associations.