The lifespan of a database object is the time over which it is defined. The valid-time lifespan of a database object refers to the time when the corresponding object exists in the modeled reality, whereas the transaction-time lifespan refers to the time when the database object is current in the database.
If the object (attribute, tuple, relation) has an associated timestamp then the lifespan of that object is the value of the timestamp. If components of an object are timestamped, then the lifespan of the object is determined by the particular data model being employed.