Oraclize is a service that aims to enable smart contracts to access data from other blockchains and the World Wide Web. This service is currently live on bitcoin and Ethereum's testnet and mainnet. What makes Oraclize so special is that you don't need to trust it because it provides proof of authenticity of all data it provides to smart contracts.
In this chapter, our aim is to learn how Ethereum smart contracts can use the Oraclize service to fetch data from the World Wide Web.
Let's look at the process by which an Ethereum smart contract can fetch data from other blockchains and the World Wide Web using Oraclize.
To fetch data that exists outside of the Ethereum blockchain, an Ethereum smart contract needs to send a query to Oraclize, mentioning the data source (representing where to fetch the data from) and the input for the data source (representing what to fetch).
Sending a query to Oraclize Oraclize means sending a contract call (that is, an internal...