Definition, Basic Principles, and Classification of Blockchain Technology

Definition : A blockchain is a distributed database that maintains a continuously growing list of records hardened against tampering, consisting of linked blocks that contain batches of transactions, timestamps, and references to previous blocks.

A blockchain — originally, block chain — is a distributed database that maintains a continuously‑growing list of data records hardened against tampering and revision. It consists of data‑structure blocks … each block contains a timestamp and information linking it to a previous block.

The earliest implementation appeared in the Bitcoin project, which has operated for nearly eight years without serious vulnerabilities, aside from a single known incident that was quickly corrected.

Historically, double‑entry bookkeeping introduced reconciliation to accounting; blockchain can be seen as the first digital ledger that embeds reconciliation directly.

In a broader sense, blockchain is a decentralized recording technology where participating nodes may belong to different organizations and do not need to trust each other; every node maintains a full copy of the ledger.

Compared with traditional databases, blockchain features immutable append‑only chains, decentralization (or multi‑centering) with minimal central control, and cryptographic mechanisms that ensure transaction non‑repudiation and privacy.

Smart contracts can be combined with blockchain to provide programmable agreement functionality beyond simple transaction recording; Bitcoin already supports simple scripting, while platforms like Ethereum enable Turing‑complete contracts.

Typical application scenarios :

Public digital‑currency chains (e.g., Bitcoin) – focus on accounting, weak or no smart contracts, PoW consensus, public chain, low performance.

Public smart‑contract chains (e.g., Ethereum) – Turing‑complete contracts, PoW/PoS consensus, public chain, limited performance.

Permissioned business chains (e.g., Hyperledger) – support multiple languages, pluggable consensus, permissioned access, consortium chain, high scalability.

Basic principles :

Transaction – a change to the ledger state, such as adding a record.

Block – a collection of transactions and a snapshot of the state, forming a consensus unit.

Chain – an ordered series of blocks that records state transitions.

If the blockchain is viewed as a state machine, each transaction attempts to change the state, and each block confirms the resulting state after consensus.

Implementation assumes an append‑only distributed ledger; new data must be placed in a new block, which is validated through a consensus mechanism before being added.

In Bitcoin, a client broadcasts a transaction, nodes package pending transactions into a candidate block, add a nonce, and perform Proof of Work (PoW) until the block hash meets a difficulty target. The winning node receives a block reward (currently 12.5 BTC) and transaction fees.

Security relies on the longest‑chain rule: as long as honest nodes control the majority of computational power, an attacker controlling less than half the network has an exponentially decreasing probability of overriding the chain, illustrated by the following probability graphs:

Classification by participants:

Public chain – open to anyone (e.g., Bitcoin).

Consortium (alliance) chain – governed by a group of organizations with permissioned access.

Private chain – controlled by a single entity with restricted participation.

Classification by purpose includes currency chains for digital money, property chains for asset ownership records, and crowdfunding chains for fundraising.