In this paper we present a temporal data model capable of representing null values in valid time based on first normal form (1NF) and temporal intervals. As opposed to previous temporal data models, we store the length of valid time intervals in our model as additional information. In our model we can find temporal information efficiently with special temporal operators. In the case where temporal information is partially known, we can derive this information as complete temporal information or use extended algebraic operations to evaluate a query. Our model is implemented using C++.