Blockchain, where do you draw the line?

Bitcoin’s blockchain is an interesting concept of decentralized database. There are various new blockchains created out there, and different levels of blockchain, some not using proof of work mining but instead some other protocol (such as raft).

Some people claim these are not actual “blockchain”, and should be named differently. Actually the concept used in Bitcoin can be found in a much older piece of software, git, in which people also build blockchain (if you consider a commit to be a block) which contains a tree linking to objects (bitcoin has a merkle tree of transactions), all of which referenced by hashes. Git allows developers to sign commits or tags, resulting in something similar than the Bitcoin blockchain (a signed commit also includes the hash of the previous commit, etc, and hash of the tree with has hash of all included files, meaning the signature results in the whole history being secured - as much as sha1 hash algorithm used by git allows).

Anyway the question I’ve come to is to define what is a blockchain and what isn’t. Is it wrong to have a blockchain without mining? Without addresses and value? What’s stopping you from calling a git repository a blockchain?

The definition for “blockchain” given by Google is: “a digital ledger in which transactions made in bitcoin or another cryptocurrency are recorded chronologically and publicly.” That is of course the current definition, but gives some basic guideline. It should be a public cryptocurrency ledger with chronological storage.

This definition is however a bit too narrow, I think. A public database recording only hashes in blocks, for example, could very well be called a blockchain. Why not?

So instead I looked at the word itself. Blockchain. A chain of blocks. So a blockchain is a database of blocks where each block contains the hash of the previous block, and where the creator of the software decided to call that a blockchain. So no you cannot call a git repository a blockchain (unless git’s creator decided to, in which case it’d be perfectly valid), and yes, all the people using the blockchain term for all sort of non-bitcoin stuff (private databases, etc) are perfectly allowed to.