Creating System Sequence Diagrams

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Creating System Sequence Diagrams
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Overview

• System sequence diagrams illustrate external
  input events to a system.
• Perform a spell check.
• Record a book loan.
• We explore
• When.
• Notation.
• Guidelines.
• Practice.

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Objectives

• Read and create system sequence diagrams.
• Identify and illustrate the system events in a
  system sequence diagram.

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A Sample Partial Process
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System Sequence Diagrams

• A system sequence diagram
• Illustrates time sequence of system events from
  actors.
• Treats the system as a black box.

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System Events

• System event.
• External input event generated by an external
  actor.
• Indicates an operation should be performed.
• Every system has at least a start() system event.

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Naming System Events

• Name system events at a high, abstract level of
  intent - not in terms of input technology.

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Example
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Artifact Relationships
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Use Case Text Sequence Diagram

• It is legal in the UML to place use case text for
  the sequence diagram to the left.
• The sentences should line up horizontally with
  the associated events.

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One Approach to Showing Output
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Inter-System Events
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Optional Exercise

• As far as possible, name and draw influence
  lines between artifacts.
• When completed, see the artifact names on the
  last page.

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Exercises

• Create a system sequence diagram for the course
  project.

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What We Learned Reflection

• System Sequence Diagram.
• Sequence of system events.
• Reflection.
• How will you use this at work?
• Relationship to other artifacts and tasks?

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Skill and Objectives Evaluation
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Terminology

• System event.
• An external input stimulus from an actor to the
  system.
• System sequence diagram.
• A diagram illustrating system events in time
  sequence order.

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Reference Sample Artifacts