The difference between BlockDAG and TxDAG
There are two levels of problems here, namely the difference between BlockDAG (block graph) and TxDAG (Transactional DAG) in a broad sense and the difference between the two in a narrow sense. In a broad sense or from the data structure, BlockDAG and TxDAG are just two different data structures. The difference is that the former will organize transactions into blocks, and the ledger is organized by blocks; while the latter does not have the concept of blocks, and the ledger is composed of transactions, which can also be understood as only one transaction in a block. Since transactions have a lot of common transaction descriptive information, that is, header information, this part of information can be stored in the block, and transactions only need to save the different parts between transactions, so the storage efficiency and transmission efficiency of BlockDAG ledger will be higher than TxDAG. In a narrow sense or from the consensus protocol, BlockDAG refers to a consensus protocol technology framework, which refers to high-performance DAG technology that can ensure security and decentralization. Because decentralization is required, it can only be based on the Proof of Work PoW consensus, so mining to generate blocks has become its important feature, so it is called BlockDAG. Qitmeer advocates the BlockDAG technology in a narrow sense, which is also the real BlockDAG technology. Therefore, it does not mean that as long as the ledger is a DAG composed of blocks, it is BlockDAG technology. Just like the community recognizes that blockchain technology is also a narrow blockchain technology, it needs to have cryptographic security guarantees and decentralized characteristics, rather than simply a distributed network where the ledger is composed of chained blocks. In fact, there have been projects with generalized BlockDAG technology, such as xDAG, but because its consensus is still centralized, Qitmeer does not recognize this as BlockDAG technology. TX DAG There is no clear definition of TxDAG in a narrow sense. From an empirical point of view, the mainstream DAG projects IOTA, OByte, and NANO happen to use TxDAG. However, these projects are all centralized to varying degrees, such as IOTA's Coordinator, OByte's witness, and NANO's DPoS, while Qitmeer is completely decentralized, which is also the biggest difference between Qitmeer and mainstream DAG projects. As for why TxDAG projects happen to be centralized, Qitmeer's point of view is that TxDAG projects may not adopt PoW for energy saving considerations, that is, no mining, and PoW is currently the truly decentralized consensus. Since there is no need for mining, there is no need for mining to package blocks, and BlockDAG insists on decentralization, so PoW consensus is required to package blocks.
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