Backtracking will unify Value and DBRef with the value resp. the database reference of successive values associated with Key in the order in which they were recorded.
Success: [eclipse]: recordz(beer, paulaner, _), recordz(beer, lowenbrau, _), recorded(beer, Value, Ref). Value = paulaner Ref = 98518 More? (;) Value = lowenbrau Ref = 98538 More? (;) no (more) solution. Fail: erase_all(beer),recorded(beer,guiness, Ref). Error: recorded(Beer,Value,Ref). (Error 4) recorded("beer",Value,Ref). (Error 5) recorded(1,Value,Ref). (Error 5)