Recoverable Schedules
Ti reads from Tj (with respect to a schedule) if Ti READs some item which had previously been WRITten by Tj.
A schedule is recoverable if no transaction in it COMMITs until all transactions that it READs from have COMMITted.
Stronger: in a strict schedule, a transaction cannot even read or write X until the last transaction which wrote X has COMMITted.