What Time Is It in the Data Warehouse?

Though in most data warehousing applications no relevance is given to the time when events are recorded, some domains call for a different behavior. In particular, whenever late registrations of events take place, and particularly when the events registered are subject to further updates, the traditional design solutions fail in preserving accountability and query consistency. In this paper we discuss the alternative design solutions that can be adopted, in presence of late registrations, to support different types of queries that enable meaningful historical analysis. These solutions are based on the enforcement of the distinction between transaction time and valid time within the model that represents the fact of interest. In particular, we show how late registrations can be differently supported depending on the flow or stock semantics given to events.