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. 2021 Nov 17;12(1):e1436. doi: 10.1002/widm.1436

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© 2021 The Authors. WIREs Data Mining and Knowledge Discovery published by Wiley Periodicals LLC.

This is an open access article under the terms of the http://creativecommons.org/licenses/by-nc-nd/4.0/ License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.

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Block structure. We show transactions with squares within blocks. The canonical blockchain is the main chain that contains blocks and continues to grow in time. New blocks are expected to be mined on the top (rightmost part) of this blockchain. Non‐transactional block data, such as block hash or nonce, are not shown in this figure, but edges indicate parents. Blocks that we depict in gray are called stale blocks because they do not appear in the canonical blockchain. At the right end of the blockchain, two blocks are competing to be the 19th block. Both blocks are valid, but eventually, the canonical blockchain will include only one of them, and the other will be a stale block. The long transactions at the top of each block are coinbase transactions (rewards of miners) which contain the sum of newly minted coins (in red) and transaction fees (in green). Block 15 has no transaction other than the coinbase one