OpenCyc

How do I represent the relationships of a person who marries in 2000, divorces in 2001, cohabits in 2002, becomes single in 2003 (i.e., stops cohabiting), marries (someone else) in 2004, becomes a widow(er) in 2005? Marital status changes over time, so I believe that PersonTypeByMaritalStatus simply cannot be Atemporal.

You would use #$maritalStatus (or #$isa) to relate the individual to one of the various instances of PersonTypeByMaritalStatus. Those assertions can go in temporal contexts (temporal microtheories) . #$PersonTypeByMaritalStatus is itself atemporal because it is a collection of collections not a collection of persons -- It has its various instances like #$Married, #$Divorced, etc. atemporally and essentially.