Generally it is the self-weight of the floor diaphragm itself plus the weight of the lower half-height walls above the floor and the weight of the upper half of the connected walls below the floor plus the weight of the two exterior half-heights of walls across the width of the diaphragm. The weight of the exterior walls on either end of the diaphragm typically aren't included as this weight load path goes directly down the wall.
Of course this all depends upon the actual load paths.
