According to CoinMeta, blockchain oracles are the infrastructure that connects blockchains to the external world, and the security of over $200 billion in decentralized finance (DeFi) relies on their proper functioning. Although smart contracts are powerful, they cannot directly obtain prices, weather data, or verify the payment status of bank accounts. The standard architecture of oracles is divided into three layers: data collection, aggregation, and on-chain delivery. Oracle nodes connect to external data providers; the aggregation layer combines multiple data points into a single value; and the delivery layer writes the aggregated values into on-chain smart contracts. Oracle issues are a fundamental tension in blockchain design that cannot be completely resolved, but can only be managed. Every decentralized finance protocol relies on the price data provided by oracles to ensure its liquidity and security.