In the previous step, we took a powerful step forward in the evolution of blockchain, from a distributed system that primarily manages ownership of digital currency that exists nowhere except within the blockchain itself, to a distributed execution environment for computer programs whose main feature is freedom from censorship. However, the usefulness of this distributed environment remains limited because the programs running in it cannot access data outside the blockchain. This step provides a way to overcome this limitation. But be warned, attempting to overcome this limitation may cost us the entire concept of a distributed system.