volume_mute

Reading a Sequence Diagram — Notation Elements

publish date: 2026/06/08 06:26:26.144030 UTC

volume_mute

The diagram below shows the sequence diagram for the View patient information use case in the Mentcare system.

What does the rectangle labeled "alt" in the top-left corner of the combined box represent in this sequence diagram?

A choice box indicating that one of the contained interactions will be executed depending on the guard condition shown in square brackets

An optional step that may be skipped if not required

An alternative actor who may also perform the interaction

An alternative version of the entire use case

Correct Answer

A choice box indicating that one of the contained interactions will be executed depending on the guard condition shown in square brackets

Explanation

The alt box (from 'alternative') is a choice box in UML sequence diagrams. It indicates that one of the contained interactions will be executed. The condition that selects which interaction is executed is shown in square brackets (guards). In this diagram, if [authorization OK] the patient info is returned; if [authorization fail] an error is returned instead.

Reference

Software Engineering, Ian Sommerville, 9th edition

Quizzes you can take where this question appears

Interaction Models