Blockchain Developer Decentralized Application Architecture 3

Question 1

What architectural problem does an oracle solve for a dApp?

Accepted Answer

It securely brings off-chain real-world data onto the blockchain

Answer

Oracles feed external data (prices, weather, events) to smart contracts, which cannot access off-chain data natively.

Question 2

A dApp needs the current ETH/USD price for a lending protocol. What is the safest design choice?

Accepted Answer

Use a decentralized oracle network with multiple data sources

Answer

Decentralized oracle networks aggregate multiple sources to resist manipulation and single points of failure.

Question 3

Why are smart contracts considered deterministic in dApp architecture?

Accepted Answer

Every node must produce the identical result given the same inputs and state

Answer

Determinism is required so all nodes reach consensus on the same state after execution.

Question 4

What is a common reason to split a dApp's logic into a proxy contract and an implementation contract?

Accepted Answer

To enable upgradeability of the logic while preserving state and address

Answer

The proxy pattern keeps a stable address and storage while the implementation logic can be swapped/upgraded.

Question 5

In an event-driven dApp frontend, how does the UI usually learn that an on-chain action succeeded?

Accepted Answer

By listening to events/logs emitted by the smart contract

Answer

Contracts emit events/logs that frontends and indexers subscribe to for state updates.

Blockchain Practice Test