Store a hierarchy and return all children
Company: Atlassian
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Onsite
Design a service to store a hierarchical tree of nodes and expose APIs.
Requirements:
- Persist a hierarchy (a forest with multiple roots is acceptable).
- Support:
1) Add a node under a parent.
2) Return **all descendants** (all children recursively) of a given node.
- Emphasis on REST API design, DB schema, and edge cases.
Deliverables:
- API endpoints and example requests/responses.
- Storage model choice (e.g., adjacency list, materialized path, nested sets, closure table) and justification.
- How to handle large subtrees (pagination) and prevent cycles.
Quick Answer: This question evaluates understanding of hierarchical data modeling, REST API design, database schema choices (e.g., adjacency list vs alternatives), and systems-level concerns like scalability, pagination for large subtrees, and cycle prevention.