It kind of depends what you need doing I supose.
Most forms of database require connectivity somewhere.
Then you'll either need to do some smart approach with the updating and retrieval, or have something local.
If you plan on making some database plugin, perhaps look into taffydb.
It is suposed to be a client side database with a simlair structure in commands like mysql database.
And wheter or not arrays are up to the task, I'm quite sure they could be, but not sure it would be the easiest approach.