Temporal Keys, Part 2 | Experimental Thoughts. One always learns new things about PostgreSQL - this time PERIOD, a data type that encompasses time spans, and EXCLUDES, another form of constraint on tables, with which overlaps of time periods can be avoided in the data design together with PERIOD. In Dynamics AX, there is something similar in the form of Date Effectivity, which goes a bit further because it also includes automatic creation of new areas, gap-free timelines, etc., while this is only the basics for non-overlapping data records. On the other hand, this can be used much more broadly, as you can formulate any EXCLUDES constraints.