Sequence diagrams in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the correct sequence diagram element for a synchronous message

In a sequence diagram, which element correctly represents a synchronous message between two objects?

A A dashed arrow with an open arrowhead pointing from the caller to the callee

B A solid arrow with a filled arrowhead pointing from the caller to the callee

C A solid line without arrowheads between two objects

D A dashed arrow with a filled arrowhead pointing from the callee to the caller

💡 Hint

Think about how synchronous calls are shown as direct requests expecting a response.

A synchronous message is shown as a solid arrow with a filled arrowhead pointing from the caller to the callee, indicating a direct call that waits for a response.

❓ Architecture

intermediate

Trace the request flow in a sequence diagram for a login process

Given a sequence diagram for a user login process involving User, Web Server, Authentication Service, and Database, which step correctly follows the user's login request?

A Database sends authentication result directly to User

B Authentication Service sends login credentials directly to User

C User sends login credentials to Web Server, which forwards them to Authentication Service

D Web Server sends login credentials to Database without Authentication Service

💡 Hint

Consider the typical flow of authentication in layered systems.

The user sends credentials to the Web Server, which then forwards them to the Authentication Service for verification before querying the Database.

❓ scaling

advanced

Estimate the impact on sequence diagram complexity when adding microservices

How does adding multiple microservices to a system affect the complexity of its sequence diagram?

A It increases the number of lifelines and messages, making the diagram more complex and harder to read

B It reduces the number of messages because microservices handle tasks internally

C It simplifies the diagram by grouping all microservices into a single lifeline

D It has no effect on the sequence diagram complexity

💡 Hint

Think about how each microservice is represented as a separate participant.

Each microservice adds a lifeline and messages, increasing diagram complexity and requiring careful organization to maintain clarity.

❓ tradeoff

advanced

Choose the best approach to handle asynchronous messages in sequence diagrams

Which option correctly represents asynchronous messages in a sequence diagram and explains its tradeoff?

A Use a dashed arrow with an open arrowhead; tradeoff is increased diagram complexity but clearer timing

B Use a solid arrow with an open arrowhead; tradeoff is less clarity on message timing

C Use a solid arrow with a filled arrowhead; tradeoff is confusion with synchronous messages

D Use a dashed arrow with a filled arrowhead; tradeoff is ambiguity in message direction

💡 Hint

Recall the standard UML notation for asynchronous messages.

Asynchronous messages are shown as dashed arrows with open arrowheads, which can make diagrams more complex but clearly indicate non-blocking calls.

❓ estimation

expert

Estimate maximum number of messages in a sequence diagram for a system with 5 components and 3 interactions each

If a system has 5 components and each component interacts with 3 others exactly once in a sequence diagram, what is the maximum number of messages shown?

A 25 messages

B 10 messages

C 5 messages

D 15 messages

💡 Hint

Multiply the number of components by the interactions per component.

Each of the 5 components sends 3 messages, so total messages = 5 * 3 = 15.