Directed acyclic graph is most used chain variant. DAG consists from events, every event nests only one datum and usualy few more hash links to another events. Events are adding by sets, forming connected graphs and called "round". Round while forming is in GDB, not in chains and could have different rules for the forming (Hashgraph, Proof-of-Time).
Events could be single-lined, like blockchain with the only one hash link - or multilined with more then one links between events. Event has links, signatures and datum inside. Signature usualy is master node signature thats placed datum from mempool to the new round
Every new data, comes from mempool produces new event in the new forming round. New round stores in GDB because events headers are not complete and could be changed - added new links, signatures and etc.