Describe the pull-based inbound oracle pattern: its problem, solution, and main trade-off.

On-chain code needs outside data, so it emits a request; the oracle catches it, fetches the data off-chain, and returns it in a transaction. Initiated on-chain — transparent, but passive and slow.

• Problem: A blockchain application needs knowledge that lives outside the chain, but a closed-world chain can't acquire it directly.
• Solution: The contract requests an off-chain state; the oracle receives that request, gathers the state from off-chain components, and sends the result back via a transaction.
• Benefit: Because the request originates on-chain, the whole exchange is transparent — you can trace on-chain whether the data was delivered (and in time) or not.
• Drawback: The oracle is passive — it only acts after it sees an on-chain request, so response time is gated by the blockchain's speed, and congestion can delay or drop the retrieval. This is a genuine request-response round trip through the chain.

Go deeper:

• Foundational Oracle Patterns (Mühlberger et al., arXiv) — the pull-based inbound pattern in full: its request-response flow, on-chain transparency, and passivity cost.