Query languages for 1NF temporal databases

There are two factors that should be considered in defining or designing a temporal database. One is that the uncertain time "NOW" should be noticed in the relational algebraic operators extended for incorporating a temporal dimension. The other is that the temporal-normal-form is closure under operators extended. We establish gap-interval-based 1NF temporal tuple calculus language and the corresponding temporal relational algebra. The query languages are given some considerations to above two factors.