Working on two version of SDN ( 3.3.0 & 4.0.0 Milestone version), Following are the things that were observed while using String[], String[][].
in 3.3.0, able to to store the single/double array's to database will null values and can retrieve them in order.
But in 4.0.0 MV, only single array is supported but while reading the order is different and storing "null" is not supported.
As it's a milestone version this issue can be solved in the final version of SDN4.