[Crm-sig] ISSUE 240: Start/End vs Period of Existence

Vladimir Alexiev vladimir.alexiev at ontotext.com
Sat Apr 19 14:00:11 EEST 2014


Hi!

(An issue that arose at public-esw-thes at w3.org under subject Re: TGN place types (broader/narrower spanning ConceptSchemes)
and was discussed to some extent between me and Richard Light)

There are many "dual" Events in CRM that indicate the Start/End of something:
- Beginning/End of Existence
- Birth/Death of a person
- Identifier Assignment with props assigned/deassigned
- Acquisition with props transferred from/to
- Transfer of Custody with props from/to
- Production/Destruction (not completely dual)
- Part Addition/Removal
- Formation/Dissolution of a group
- agent Joining/Leaving a group

There are also events that indicate Start, without a corresponding End event:
- Creation (End is not appropriate, since conceptual things are forever)
- Type Assignment (IMHO should also have "type deassigned", just like Identifier Assignment)

HOWEVER, there is no standard way to state the "Period of use/existence/activity of something", such as:
- period of use of an Identifier (Appellation, Title), Type
- life of a Person
- floruit of a Person
- period of group membership or profession of a Person (e.g. reign)
One would have to model them as Event/Activity in which the concerned entity participated, with some P2_has_type.

We also need to relate the start/end events to the period of existence.
P116_starts and P115_finishes almost fit the bill, though they bind only one of the endpoints.
E.g. P115: "allows the ending point for a E2 Temporal Entity to be situated by reference to the ending point of another temporal entity of longer duration".
P115 makes no relation between the starting points. But Death is *the* end of Life, so *both* points of Death must be strongly related to the ending point of Life.
- We could introduce sub-properties:
  P216 really starts (really started by): "an E2 Temporal Entity (e.g. Birth) is considered to be "momentary", and is the start of a longer E2 Temporal Entity (e.g. Life)"
  P215 really finishes (really finished by): "an E2 Temporal Entity (e.g. Death) is considered to be "momentary", and is the finish (end) of a longer E2 Temporal Entity (e.g. Life)"
- These should be subproperties not only of starts/finishes, but also of forms_part_of :
  P216_really_starts rdfs:subPropertyOf P116_starts, P9i_forms_part_of.
  P215_really_finishes rdfs:subPropertyOf P115_finishes, crm:P9i_forms_part_of.
(This is optional, we could just use P116 and P115)

Finally, we need some rules to relate the 4 time-points (P82a, P81a, P81b, P82b) of the Start/End events to those of the Existence period.
I'm not sure what the rules should be... One approach could be that:
- Start/End are considered "momentary" events, thus have only 2 points (P81a=P82a, P82b=P81b)
- these points correlate to Existence as follows: Start.P82a=Existence.P82a, Start.P82b=Existence.P81a, End.P82a=Existence.P81b, End.P82b=Existence.P82b.
Maybe this is a bit naïve, since:
- "momentary" is a relative term. Birth could be described as a minute event, usually is described as an 
 the "expected" inequalities P82a<=P81a<=P81b<=P82b do not always hold, see
  Deducing event chronology in a cultural heritage documentation system (Holmen & Ore, CAA 2009)

Modeling such Periods of Existence is significantly more economical than modeling with Start/End events.
So I think this is a new important shortcut pattern: one event (e.g. Life) being the shortcut expression of two events (Birth/Death).
I expect the classical objection will be raised, that Life is not used often in cataloging practice.
But if there's enough interest to have explicit classes for Birth/Death, how can there be not enough interest to have specific class for Life?

In the attached Turtle file I've defined a couple of extension classes (Life and Membership) and given some examples.
Note that Joining/Leaving are longcuts of Membership, which itself is a longcut of P107_has_current_or_former_member.
So it's interesting that we've discovered an expression at intermediate level of detail between super-detailed (Joining/Leaving) and undetailed (P107)

I give an example of a king whose reign finishes with his life (descension coincides with Death).
It would be interesting to try to model Picasso's creative periods with this machinery, e.g. see
http://en.wikipedia.org/wiki/Picasso
http://en.wikipedia.org/wiki/Picasso%27s_Blue_Period

Cheers! Vladimir
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