Sequence diagrams in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a sequence diagram?

A sequence diagram shows how objects or parts of a system talk to each other over time. It uses arrows to show messages sent between them in order.

beginner

What do vertical lines represent in a sequence diagram?

Vertical lines represent the lifelines of objects or components, showing their existence over time during the interaction.

beginner

What is the purpose of arrows in a sequence diagram?

Arrows show messages or calls sent from one object to another, indicating the flow of communication and the order of events.

intermediate

How do sequence diagrams help in system design?

They help visualize how parts of a system interact step-by-step, making it easier to understand, design, and debug complex processes.

intermediate

What is an activation bar in a sequence diagram?

An activation bar is a thin rectangle on a lifeline that shows when an object is active or processing during the interaction.

In a sequence diagram, what does a horizontal arrow represent?

A The lifespan of an object

B A data store

C A decision point

D A message sent between objects

Horizontal arrows show messages or calls sent from one object to another.

What does a lifeline in a sequence diagram show?

A The user interface layout

B The data stored in a database

C The timeline of an object during interaction

D The network connection status

Lifelines are vertical lines that represent the existence of an object over time.

Which element indicates when an object is active in a sequence diagram?

A Activation bar

B Lifeline

C Message arrow

D Note

Activation bars show when an object is performing an action or processing.

Sequence diagrams are mainly used to:

A Show the order of interactions between system parts

B Design database schemas

C Create user interface layouts

D Monitor server health

Sequence diagrams focus on the order and flow of messages between components.

What does a dashed arrow usually represent in a sequence diagram?

A New object creation

B Return message or response

C Error message

D User input

Dashed arrows typically show return messages after a call.

Explain the main components of a sequence diagram and their roles.

Think about what shows objects, communication, and timing.

Describe how sequence diagrams help in understanding system behavior.

Consider how seeing steps in order helps design and debugging.