Since blockchain theory is under active development, the set of common notations and concepts is not well established. Professional researchers, observers, enthusiasts and casual people give different meaning to certain words. Apparently, the word "blockchain" is the most confusing word in the blockchain space. In this setting it's important to study all definitions, their consequences and possible confusions.
Blockchain as a data structure
The most narrow definition of the blockchain is below.
Definition 1. Blockchain is a sequence of data records called blocks in which every next block contains the hash of the previous one.
This definition narrows the concept of blockchain to some data structure that solves the problem of data immutability. Many newcomers understand the blockchain in this narrow fashion. Also this definition was a "start point" for blockchain technology. Many experts highlight that the first blockchains were invented were invented in 90s. If we accept the definition above then this claim is correct. However, this viewpoint on the blockchain is outdated since invention of the Bitcoin by Satoshi Nakamoto has extended the original concept.
Nevertheless, this narrow viewpoint on the blockchain technology is often purportedly exploited.
- First, there are many projects that assign the name blockchain to their products. Blockchain technology has attracted lots of interest, no surprise, people try to exploit its popularity for marketing purposes. Rebranding of databases into blockchains has caused the emergence of "private centralised blockchains". These solutions obviously don't have advantages of public decentralised blockchains.
- Second, in contrast to the previous category, there is a dozen of projects that claim their product is not a blockchain but some more advanced data structure that overcomes the limitations of the blockchain technology. The typical example here is a directed acyclic graph or DAG. Supporters of aforementioned projects often speculate that DAGs could be useful for solving blockchain scalability problem. These speculations are often incorrect and misleading.
Blockchain as a record of state transitions
Definition 2. Blockchain is a sequence of state transitions
Blockchain as a protocol
Blockchain as a decentralized network
Definition 4. Blockchain is a decentralised database managed by computers belonging to a peer-to-peer network instead of a central computer like in traditional databases. Participants of the network wish to agree upon a sequence of events and the order in which they occurred.
Blockchain as a technology
For many people potential of blockchain as a technology is more important than a concept of blockchain itself.
Definition 5a. Blockchain is a disruptive record-keeping technology capable that capable to solve problem X related to decentralisation, database immutability, data management or data processing.
Blockchain as an industry
- Blockchain Was Born 20 Years Before Bitcoin. Forbes.
- Understanding Directed Acyclic Graphs in the Blockchain Landscape. Cointelegraph.
- What Is a Directed Acyclic Graph (DAG) in Cryptocurrency?. Binance Academy.