Blockchain and its Alternative Distributed Ledgers - A Survey

Blockchain as a distributed data structure or ledger is perceived to provide solutions in manifold areas beyond their prominent form of digital currency; they also showed several challenges. As enhancements to the existing blockchain systems are being proposed and developed, alternative underlying data structures were driven to solve some of the challenges facing them whilst maintaining their key ideas. We start by explaining the key concepts of the blockchain as implemented in Bitcoin and Ethereum. From there, we explain the challenges and survey on the alternative data structures along with their consensus mechanisms. We find a generalization in using hash pointers in the alternative data structures and unfold the current research and implementation directions for solutions to the challenges.