3.2 INTERVALS

and an ocean tumbled by with a private boat for Max

and he sailed off through night and day

and in and out of weeks

and almost over a year

to where the wild things are.

Maurice Sendak, Where the Wild Things Are

And which of you by being anxious can add one cubit to his span of life?

Matthew 6:27

An interval is an unanchored contiguous portion of the time line. An interval is relative; an instant is absolute. An interval can be added to an instant, yielding another instant. Intervals cannot be added to spatial points, nor spatial intervals (such as cubits) to temporal intervals, except as (often highly effective) literary devices, as the above quotes illustrate.

The distance between two instants is an interval. Unlike instants, intervals have direction. An interval can be positive or negative, denoting a shift to the future or to the past.

Intervals are less prominent in the FINDER schema than instants. Some are signaled with "duration" or "interval" in their name, examples being the Period_Durtn column in Well_Test_Period and the Sampling_Interval column of the Seis_Survey_Hdr table, or by mentioning the time during which something was happening, as in the Time_String_In_Hole column of the Well_Log_Service table. Other interval columns are more obscure, such as the Incrmnt_Time column of the Stage_Flowback table (other columns having...