BlockDAG

A Block Directed Acyclic Graph (BlockDAG) is a data structure used in blockchain-like networks where blocks are arranged in a graph instead of a strict chain. Traditional blockchains (like Bitcoin) have a single chain of blocks, but this can cause bottlenecks only one block is added at a time. BlockDAG allows multiple blocks to be added simultaneously, improving throughput.

The difference from Blockchain:

Blockchain is a single chain of blocks , minor block wins where others discarded and has lower throughput. Whereas BlockDAG Single has Multiple blocks coexist and are referenced, has higher throughput and locks in a DAG reference multiple previous blocks, not just one. This allows blocks found at the same time to both be included in the ledger. Transactions are confirmed once enough blocks approve them in the DAG.

Structure

It is directed in every link (edge) between blocks has a direction (from older to newer).It has no loops are possible; you can’t go from a block back to itself. Instead of a line, it’s a network of blocks.

Consensus Mechanisms

PHANTOM / GHOSTDAG: Color and order blocks to agree on a main “blue” set.

SPECTRE: Vote on the ordering of transactions using block relationships.

Hybrid PoW/PoS: Combines proof-of-work for security and DAG for throughput.

Advantages

It has higher throughput  which Supports many transactions per second (TPS).

It supports faster confirmations since multiple miners’ work is used.

There are no orphan wastes because  parallel blocks aren’t discarded.

It has better scalability which suitable for high-volume networks.

Applications

It is used in Cryptocurrencies:

Kaspa, Conflux, Fantom, Nano.

It is used in IoT networks:

Devices generate many microtransactions; DAG suits low-cost, fast settlements.

It is also used Smart contracts & DApps:

Faster execution with reduced block conflict delays.

Challenges

It has Complexity of ordering transactions is harder than in a single chain.

It needs robust consensus to avoid double-spending.

It adopts most infrastructure and developer tools are blockchain-focused.

Real-world Examples

Kaspa (GHOSTDAG) it uses pure BlockDAG.

In Conflux  it combines tree-graph and blockchain features.

Fantom (Lachesis DAG) uses DAG-based smart contract platform.