Mastering Blockchain Programming with Solidity

Blockchain depends on off-chain oracles

On their own, a blockchain is a separate network. It uses P2P networking over the internet to keep sharing transactions between nodes, but it does not have a way to get the data from outside (such as any data present on the internet, other than blockchain data) of the blockchain network, also known as off-chain data.

For example, the Ethereum blockchain cannot fetch any data from the internet on its own. There are some third-party developed Oracle services; by using them, you can fetch the data from the internet to the blockchain and do your transactions.

If your application is highly dependent upon third-party data available on the internet, then you should not use blockchain. If your off-chain data ...