Support for multiple start/end dates for a historical place

[kintopp]

Up to now, we've worked with a simplified notion of the start and end of a (historical) place on the assumption that it came into existence on some year and dissolved at some later year. But the historical record is more complex.

Take for example the Duchy of Opole and Racibórz. According to Wikipedia (for the sake of argument, let's just assume the data there is correct), it came in and out of existence several times:

1202–1281
1521–1532
1551–1556

Are we able to model these intermittent states of existence in its own place record? In this entry, since we are dealing with the place 'as such' we need to record 1202-1281 as well.

[gklyne]

The model, as documented in
020180305-EMPlaces-data-model-using-annotations.pdf, supports links to multiple em:Time_period values. (It's not blindingly obvious, but the double arrowhead is used to indicate multiple values are allowed).

But I also note that, when working on name attestation
20180622-EMPlaces-Opole-name-attestation.pdf, I ended up separating "Timespan" from "Time period" (sort of like PeriodO periods vs actual date ranges). In doing this, do we want to allow multiple date ranges for a time period, or multiple time periods for a place?

This is an area where I'd like to see what others are doing (e.g. @kgeographer with his linked pasts network).

[gklyne]

See also: LinkedPasts/linked-places-format#5 - ideally, I'd align with this work, but as it stands I have some problems.

(Also, when I recently reviewed this, I concluded that the time period ranges for places in the historical hierarchy could be inferred from from the relationship ranges. And the labels for the different full-hierarchies would have to be inferred as they don't relate to any single place.)