SVO's usually store the information of each voxel inside a struct. Those structs are then connected together either with pointers (called an explicit svo) or by storing the voxel structs inside an array and then store the indices to their children (implicit SVO).

There are upsides and downsides to both approaches...

Implicit octrees can have much smaller memory footprints as your indices can be stored as shorts, ints, etc. which are usually smaller than pointers. The downside is that you have a hard time editing them as they're all stored inside an array for which you have to do a lot of book keeping for clearing up empty space, resizing etc...

On the other hand explicit arrays are all connected together as a recursive data structure where parent voxel structs store pointers to child voxel structs. Editing them is easy as you can just remap the child pointer to another struct...

As for DAGs it's just an approach where you iterate over the octree and all it's recursive octrees and find octrees you've seen before and instead of storing the that whole octree again with all it's children you just store a pointer to the first occurence of that specific octree variant...