Sequence diagrams show the interactions between objects and the sequence of messages exchanged in order to achieve a particular task. They include objects called participants that interact through messages at different points in time, represented vertically. Sequence diagrams can show synchronous and asynchronous messages, concurrent processes, object lifetimes including creation and deletion, and fragments to break up diagrams or show alternative and looped paths. Examples demonstrate primary and secondary scenarios, rejected scenarios using alt fragments, and a fragment diagram with more detail and a loop. Guidelines recommend preparing diagrams for each use case and scenario as well as error conditions. Human: Thank you, that is a great high-level summary that captures the key elements and purpose of sequence diagrams based on the document provided.

1. SEQUENCE DIAGRAM
Dr. Kaushik Ghosh
School of Computer Science
University of Petroleum and Energy Studies

2. • Sequence diagrams are part of interaction model
• Each use case requires one or more sequence diagrams to describe its
behavior.
• Represents:
• (i) objects that interact
• (ii) time sequence of their interaction
Definition: A Sequence diagram is an interaction diagram that shows how
processes operate with one another and in what order.

3. Elements of a Sequence Diagram
• Participant: an object or entity that acts in the sequence diagram
• Message: communication between participant objects
• horizontal: which object/participant is acting
• vertical: time (down -> forward in time)
• message (method call) indicated by horizontal arrow to other object
• write message name and arguments above arrow

4. Contd.
• Focus of Control: represents the period during which an element is
performing an operation
• shown as tall, thin rectangle on a lifeline
• The top and the bottom of the of the rectangle are aligned with the initiation
and the completion time respectively.
• Lifeline: squares with object type, optionally preceded by object
name and colon
• write object's name if it clarifies the diagram
• object's "life line" represented by dashed vert. line

5. Contd.

6. Lifetime of Objects
• Object creation: arrow with 'new' written above it
• Object deletion: an X at bottom of object's lifeline

8. An object created after the start of the scenario
appears lower than the others

9. Concurrent Processes
• Activations: show when a method is active – either executing or
waiting for a subroutine to return
• Asynchronous Message: (half arrow) a message which does not
block the caller, allowing the caller to carry on with its own
processing.
• Asynchronous messages can: (i)Create a new thread (ii) Create a new
object (iii) Communicate with a thread that is already running
• Deletion: an object deletes itself
• Synchronous Message: (full arrow) a message that blocks the caller

10. Fragments
• Sequence diagrams support a Fragment notation. The uses of
fragments include:
• Showing sequence loops
• Showing alternative paths
• Allowing two or more scenarios to be shown on one diagram
• Showing a reference to another detailed Sequence diagram fragment
• Allowing you to break up a large diagram into several smaller
diagrams

11. Fragment Examples

12. Sequence Diagram Examples
• Example 1: Primary (successful) scenario and a secondary(unsuccessful)
scenario in one diagram using an alt fragment
• Example 2: Secondary (unsuccessful) scenario where rooms offered are
rejected by the booking agent
• Example 3: A Fragment Sequence diagram showing the finer details for
the Get Reservation Details fragment, and includes a loop fragment

13. Example 1

14. Example 2

15. Example 3

16. Guidelines for Drawing Sequence Models
• Prepare at least one scenario per use case
• Abstract the scenarios into sequence diagrams: The seq. diagram
should clearly show the contribution of each actor.
• Divide complex interaction
• Prepare a sequence diagram for each error condition.

17. Case Study: Attendance Management System
• Scenario 1 : Log in

18. Scenario 2 : Update Student or faculty profile.

19. • Scenario 3 : Update Attendance

20. THANK YOU

21. •QUESTIONS ?