Complex sentence: By contrast, a temporal database qualifies each row with a valid time "period" or valid time "interval", thus asserting the fact that "John Smith" was a member of staff between 1 June 2001 and now.
Split into simpler sentences: By contrast, a temporal database qualifies each row with a valid time "period" or valid time "interval". For example, we can assert the fact that "John Smith" was a member of staff between 1 June 2001 and now.