Machine Learning in/for Blockchain: Future and Challenges

Each block contains a certain amount of data; and the chain connects these data to form a distributed database. New block needs to be approved by all or some of the network members to become a valid block. Each approved block includes information of the previous block in the chain, therefore if the block is changed, all blocks before this block will be invalid as well. The strategies to reach agreement of the new block (consensus) vary in different types of blockchain. The mathematical structure of the blockchain implies two essential properties: (i) the data (in block) is immutable; (ii) the distributed network with consensus allows users to communicate directly with each other and download a copy of the current ledger, which means that there is continuous monitoring and redundancy of the data in the network.