ALLEN RELATIONSHIP AND OTHER QUERIES - Managing Time in Relational Databases - page 313

It says that P 1 and P 2 either start or end at the same time, but
do not both start and end at the same time.
This relationship has no inverse.
Consider the following request for information: which
policies either began when the Diabetes Management Wellness
Program for 2009 began, or ended when that program ended,
but not both?
The SQL written to fulfill this request is:
SELECT * FROM V_Allen_Example
WHERE ((pol_eff_beg_dt ¼ wp_eff_beg_dt
AND pol_epis_end_dt < wp_epis_end_dt)
OR (pol_eff_beg_dt > wp_eff_beg_dt
AND pol_epis_end_dt ¼ wp_epis_end_dt))
AND NOT(pol_eff_beg_dt ¼ wp_eff_beg_dt
AND pol_epis_end_dt ¼ wp_epis_end_dt)
P 1 [during] P 2
This is a pair of relationships, one the inverse of the other. In
the non-superscripted relationship, the first time period is the
shorter one.
Time Period Relationships
Along a Common Timeline
Intersects
Fills
Occupies
During
|-----|
|------------|
Figure 14.5 P 1 [during] P 2 .