The block DAG is how the blockchain is represented, as a directed acyclic graph. Technically speaking, it's a tree, since child blocks cannot link to parent blocks (the parent pointer is defined as a block hash; colliding the block hash is infeasible).
In the database, the block DAG is implemented on blocks. Though a more purer implementation would simply be based around hashes. e.g. something like a set of edges/vertices.
The block DAG is how the blockchain is represented, as a directed acyclic graph. Technically speaking, it's a tree, since child blocks cannot link to parent blocks (the parent pointer is defined as a block hash; colliding the block hash is infeasible).
In the database, the block DAG is implemented on blocks. Though a more purer implementation would simply be based around hashes. e.g. something like a set of edges/vertices.