[1][2][3] Relational operators, such as join, are generalized to support a natural treatment of interval data, such as sequences of dates or moments in time, for instance in temporal databases.
[5] Date et al. have also given the following definition: Relvar R is in sixth normal form (6NF) if and only if every JD [Join Dependency] of R is trivial — where a JD is trivial if and only if one of its components is equal to the pertinent heading in its entirety.
Sixth normal form is intended to decompose relation variables to irreducible components.
For instance, if a relation comprises a supplier's name, status, and city, we may also want to add temporal data, such as the time during which these values are, or were, valid (e.g., for historical data) but the three values may vary independently of each other and at different rates.
[8] The sixth normal form is currently as of 2009 being used in some data warehouses where the benefits outweigh the drawbacks,[9] for example using anchor modeling.