Blockchain Data Structures: How Transactions Are Organized and Verified

A blockchain is often described as a database shared across networked computers. In Ethereum.org’s introductory explanation, blocks cryptographically reference earlier blocks, while nodes use consensus to agree on state. That description is a useful starting point, but it is not a universal specification: blockchain designs differ in participation, consensus, data visibility, finality, and execution capability.

A useful way to approach blockchain data structures is to separate three questions: how transactions are represented and grouped, how blocks relate to earlier blocks, and how a network represents the effects of transactions as state. These structures organize information and can support particular checks. Their presence alone does not establish every fact about a transaction or network.

What blockchain data structures do

A blockchain generally combines related structures rather than relying on one universal format. Transaction records have a network-specific meaning. Blocks arrange records into a history. A network’s state reflects the results of transactions under its rules. The particular structures and their relationships depend on the blockchain being described.

The evidence available for this overview supports two bounded examples. Ethereum transactions are cryptographically signed instructions from externally owned accounts that can transfer value or invoke contract code and change network state. Bitcoin’s UTXO transaction model instead describes inputs that spend specific earlier outputs. These examples illustrate different transaction relationships, but do not establish a complete comparison of the networks’ internal state representations.

It is also important to distinguish a data structure from the conclusions someone may draw from it. A record’s presence in a structure, a relationship between hashes, and a network’s agreement about state are different matters. To understand a particular blockchain, readers need its own technical documentation for the structures and rules at issue.

Transactions and blocks

A transaction is data interpreted according to a network’s rules. Its fields and effects are not interchangeable across protocols. In Ethereum, a transaction is a cryptographically signed instruction from an externally owned account; it can transfer value or invoke contract code and change network state. Contract-generated calls and token movements can occur during execution, but they are not separate top-level transactions from externally owned accounts.

Bitcoin’s transaction guide describes a different relationship. A non-coinbase transaction input spends a specific prior transaction output, identified by its transaction ID and output index. New outputs remain unspent until a later input spends them. This lets a reader follow the referenced output and the input that spends it without treating the input as an account-balance update.

These examples show why generic labels need care. “Transaction data” may refer to a signed instruction, an input’s reference to an earlier output, or other protocol-defined information. The accepted evidence here does not establish a universal block layout or specify how every network orders transactions within a block. For a particular chain, check its protocol documentation before assuming which records a block contains, what order they have, or how their positions are represented.

Blocks and linked history

Ethereum.org describes an Ethereum block as cryptographically referencing its parent, creating an ordered chain of network state. This is a network-specific example of block linkage; other networks can use different data structures and consensus rules.

A parent reference connects a block to an earlier block in the described history. The reference is a cryptographic relationship, not by itself a complete account of which history the network accepts. Ethereum.org’s introductory description also identifies consensus as part of how nodes agree on state. Therefore, a statement that blocks are linked should not be expanded into a claim that linkage alone determines network acceptance.

The supplied technical evidence does not provide a supported field-by-field account of block headers, nor does it establish which header fields are common across blockchains. It is safer to treat “block header” as a network-specific term whose contents must be checked in that network’s documentation, rather than asserting a standard set of fields or a universal transaction commitment in every header.

Transaction commitments and Merkle trees

Cryptographic commitments and Merkle trees are often discussed as ways to summarize data and check membership. However, the accepted sources supplied for this article do not establish how a Merkle tree is constructed, how transaction hashes are combined, what an inclusion proof contains, or how different implementations handle tree variants. Without an authoritative technical claim supporting those details, a generic walkthrough of leaves, parent hashes, roots, or sibling-hash paths would go beyond the evidence available here.

For a particular network, consult primary technical documentation to determine whether it uses a transaction commitment, how that commitment is formed, and how a proof is verified. A membership result, where a protocol supports one, must be interpreted relative to the relevant commitment and verification rules. The evidence in this source pack does not support a general description of proof formats or a claim that such a proof alone identifies a containing block or establishes that the block was accepted.

Transaction history and state

Transaction history and network state are related concepts, but the supplied claims do not define a universal state structure. Ethereum transactions can change network state, and Ethereum.org describes nodes as using consensus to agree on state. These points do not specify how Ethereum stores state internally or justify general claims about state databases, authenticated state structures, pruning, or archival storage.

The Bitcoin source supports a narrower description: a non-coinbase input spends a specific prior output, and newly created outputs remain unspent until later spent. This is the stated UTXO transaction relationship. It should not be turned into an unsupported account-based-versus-UTXO comparison of internal state representation. The evidence provided here does not establish that broader comparison or show that authenticated state structures are universal components.

When a technical description discusses a network’s state representation or storage behavior, check documentation for that network and the relevant implementation. Transaction-level examples can clarify how particular records refer to one another, but they do not settle how every node represents or stores the resulting state.

What the supported structures establish—and what remains open

The supplied claims support a few limited conclusions:

  • Ethereum blocks cryptographically reference parent blocks, creating an ordered chain of network state.
  • Ethereum transactions can change network state, but a top-level transaction is distinct from contract-generated calls and token movements during execution.
  • A Bitcoin non-coinbase input identifies a specific prior output that it spends; new outputs remain unspent until later spent.
  • Blockchain designs differ in participation, consensus, data visibility, finality, and execution capability.

Those claims do not, on their own, specify a universal header format, transaction ordering convention, Merkle-tree construction, inclusion-proof procedure, or state database design. Nor do they establish a general checklist separating data integrity, transaction validity, consensus acceptance, data availability, and truth about off-chain information. Those distinctions may be important when evaluating a particular system, but this source pack does not supply the technical evidence needed to explain them in detail.

Accordingly, a claim that something has been “verified” needs a precise object and context. Ask what data or relationship was checked, which network’s rules apply, and what source supports the result. Do not infer more than the stated check establishes; the accepted claims here do not document a general proof method or security guarantee.

A practical mental model

When reading an architecture description, ask three questions:

  1. How are transactions represented? Identify the network-specific meaning of a transaction and the relationships its inputs or instructions describe.
  2. How are blocks connected? Check whether the documentation describes parent references or another structure, and keep that description separate from consensus rules.
  3. How is state represented or committed? Look for network-specific documentation rather than assuming that a transaction model reveals the full state or storage design.

Use examples only within their documented scope: the parent-block relationship and transaction description cited here are Ethereum examples; the input-output relationship is specific to Bitcoin’s UTXO model. Before applying terms such as “header,” “Merkle proof,” or “state structure” to a named blockchain, consult authoritative technical documentation that supports the relevant details. This keeps the explanation grounded: data structures organize and relate information, while the exact checks and conclusions depend on the protocol evidence available for that network.

Sources and references