1.3.6 Resolving Feedback System Sequence Diagram Errors

Feedback Identifies a Difference in the Interaction Model

A sequence diagram should communicate:

  • which objects participate;
  • which object sends each message;
  • which object receives each message;
  • which method is called;
  • the order in which calls occur.

When the Feedback System reports a sequence-diagram error, treat the message as evidence that one of those elements differs from the expected interaction.

Identify the Error Category First

Common introductory sequence-diagram problems include:

  • missing participant;
  • incorrect object identity;
  • incorrect object type;
  • missing message;
  • incorrect method name;
  • message sent to the wrong object;
  • messages in the wrong order;
  • extra message that is not part of the required interaction.

Class-diagram field errors and object-diagram value errors belong to different UML forms.

Compare the Message Receiver

Suppose the expected interaction is:

Sequence diagram showing read current feedback, then identify the exact participant message difference, then compare with the current interaction, then revise one focused element, then save the editable Violet file, then submit the current file.
ReadCurrentFeedback.
  • New
  • Changed
  • Removed
Do Not Guess from Visual Symmetry

A sequence diagram is not correct because the arrows look balanced or evenly spaced.

Meaning comes from:

  • participant identity;
  • direction;
  • message name;
  • order.

Model the source interaction rather than arranging arrows for appearance.

Read the Revised Diagram as a Story

For example:

If the diagram cannot support that sentence, the interaction is still unclear.

Feedback Should Lead to a Better Model

The goal is not only to remove the Feedback System error.

The goal is to make the diagram accurately represent the required method-call interaction.