I'm not sure if you still need an answer.

So, for now, I just clarify that subscribe tells you when some client needs the updates related with a row; moreover, the supplied item name tells you which row.
For this reason, you have to predetermine the item names in such a way that they refer to rows; the obvious way is using a unique key field associated to the rows.

Once you have received the request through subscribe (and until you receive unsubscribe), it's up to you to observe the row and send updates upon changes (and the initial row contents as the snapshot, if needed).
I would prefer not to suggest a way of doing that; just note that, as shown in the tutorial, that should be performed by your own threads.