Is the universe a directed acyclic graph
Directed acyclic graphs (DAG) - are graphs that are directed and have no cycles connecting the other edges. This means that it is not possible to traverse the entire graph starting at an edge. The edges of the directed graph only go in one direction. The diagram is a topological sort where each node is in a specific order. The DAG construction consists of corner points that are connected by edges. The main algorithm of the DAG is called topological ordering. This means that each edge is directed from an earlier edge to a later edge.
DAGs are very popular with the crypto squad right now. Mainly because IOTA and other projects use them.
DAG is easy to explain as you go step by step. It's actually the same as blockchain. If you divide this word into "block" and "chain" it becomes much clearer. Let's do it again with DAG. It's a graph - OK. It's acyclic - it doesn't have cycles connecting nodes. If you follow the diagram from node to node, you will never visit the same node twice. And it's directional - the edges of the directed graph only go in one direction.
So DAG is a graph where edges go in one direction and have no cycles - you will never get to the beginning or the same node.
- Next - the DAG construction, which consists of nodes and edges.
- Node - each node represents an object or a unit of data.
- Directed edges. A directed edge (or "arrow") from one node to another represents some sort of relationship between those two nodes. In our situation, the arrow means "based on".
- A root node. At least one of the nodes has no parents. This is the root of the DAG.
- Leaf knot. One or more nodes have no children. They are called leaves or leaf knots.
The DAG algorithm is called topological ordering. This means that each edge is always directed from an earlier edge to a later edge. DAGs are often referred to as competitors of the blockchain or even the next generation of the blockchain.
Blockchain against DAG 
Actually, the blockchain and DAG are more related, but still competitors. Both terms are actually distributed ledgers. The blockchain is a linear distributed ledger and the directed acyclic graphs are the ones without any blockchain. In the cryptocurrency world, the blockchain and the distributed ledger are becoming synonyms, but it's not entirely true - DAGs are ledgers without a blockchain.
DAG has obvious advantages over blockchain:
- DAGs have good scalability, which means the high speed of transactions. The only checkers and checkers of transactions are nodes, not blocks. The information is in transactions, which means that it is very quick. In theory we speak of millions of transactions per second. It's very good news for DAGs cryptocurrency;
- Greater reliability. Thanks to the DAG construction, all transactions are always verified by other nodes, sometimes more than once;
- No energy wasting PoW mining. There are no miners at all. That also means more decentralization;
- The DAGs algorithm is ideal for the micro-payment system as it has "almost zero" commissions.
Of course, DAGs are not a panacea for blockchain and cryptocurrency, and it has its own limitations. Most importantly, despite a million possible transactions, the DAG still has limits. Who knows, maybe we'll talk about the DAG scalability problem in the future. Another doubt is that there is no information about system failure protection in its algorithm or design.
DAG coin: IOTA 
One of the top coins with DAG is IOTA. This project is in TOP-10 at coinmarketcap.com with almost $ 5 billion capitalization. The IOTA name comes from the «Internet of Things», and the basic idea of this cryptocurrency project is to create an ecosystem for billions of micro payments. Because in the near future, all of our devices will be connected to the internet and do a lot of transactions. Billions of payments with free commissions - it's an ideal ecosystem for the DAG algorithm.
The "cooperation" between IOTA and DAG led to the Tangle. The construction of IOTA DAG is even wider - according to the whitepaper, it looks like 3D-directed acyclic graphs. Each transaction in Tangle must confirm two previous transactions that the network chooses at random. The algorithm of this cryptocurrency associated with DAGs also makes it possible to create parts of the network offline. When connected to the Internet, these clusters became part of the general “blockchain”. Also, there is one advantage of IOTA that is not associated with DAG - the resistance of quantum computers, because of the different methods of cryptography. At the end of May, the IOTA Foundation presented Trinity Mobile Wallet.
DAG coin: Byteball 
Byteball cryptocurrency project takes advantage of DAG to create the smart contracts ecosystem for fast payments and storage of financial data: currencies, property titles, debt, stocks and more. This non-blockchain project, based on the DAG construction, is already working and has a good and user-friendly wallet.
Byteball is good when it comes to peer-to-peer smart contract. Byteball users can use risk-free conditional smart payments - all they need to do is set a condition when the recipient receives the money. If this condition is not met, your money will be sent back to you automatically - a very simple algorithm based on DAG. For example, Byteball enables peer-to-peer insurance to be bought and sold on its platform using a smart contract.
Given the KYC / AML requirements of the current financial world, it is good that Byteball is giving customers the ability to link their Byteball address to their real identity via the Jumio service. But there is a place for some anonymity in Byteball. Project has two currencies - bytes (GBYTE) and blackbytes. Bytes are the commonly used currency on Byteball's platform, and all transactions are public. Blackbytes gives users complete privacy when needed. Blackbytes are a cashless, incomprehensible currency, the transactions of which are not visible in the public database.
And the last interesting thing is that bytes are available absolutely for free. You just need to have bitcoins (BTC) and link your bitcoin address to the byte address.
DAG coin: Dagcoin 
It looks like a scam based on the facts and information from various online sources. Their page on GitHub is closed with the warning "Dagcoin is a Ponzi pyramid scam promoted by known scammers" in the title. You can also search the internet for more information about Dagcoin yourself.
Other signs of fraud are that they use many websites for advertising - dagcoin.org, dagcoin.group, dagcoin.club. Every online source is full of loud phrases like "The most usable cryptocurrency in the universe," but this cryptocurrency is not traded on any exchange, and you cannot find it in coin markets. Also, there is no information on what Dagcoin is doing. You only pay a little USD to get Dagcoin and some "educational materials".
The founder of Dagcoin is Nils Grossberg - but this man was the head of OneCoin, a “successful” MLM cryptocurrency project that earns money by inviting new members. And the same goes for Dagcoin - you can earn Dagcoins in the same way and receive your 10% from newcomers and even «Leader Rewards» (information from the Russian-language dagcoin.club). In addition, you cannot get all of your dagcoins - at least 35% must remain in your account (source - dagcoin.club).
According to the information above, Dagcoin has some obvious signs of a scam project. But there is no information about investigations against it or the closing of this project.
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