[crm-sig] Issue 4, scope notes

martin martin at ics.forth.gr
Tue Jan 29 21:45:29 EET 2002


Dear All,

In Paris we decided to add to the E2 Temporal Entity the well-known temporal relationships from
J.F.Allen, 1983, which can be fairly regarded as a standard in Knowledge Representation.
I terms of directed, bidirectional properties as we use in the CIDOC CRM, they can be defined as:

before (after) :                               E2 Temporal Entity
     meets in time (met-by in time):    E2 Temporal Entity
     overlaps in time (overlapped-by in time):   E2 Temporal Entity
     during (includes in time):                          E2 Temporal Entity
     starts (started-by):                        E2 Temporal Entity
     finishes (finished-by):                   E2 Temporal Entity
     equal in time:                                E2 Temporal Entity

where the postfix "in-time" is used to disambiguate from spatial or spatiotemporal relationships, that appear
lower in the IsA hierarchy of entities in the CIDOC CRM.

Here my proposal for a scope note:

The temporal relationships relate a Temporal Entity X, the domain, with a Temporal Entity Y, the range.
Let us denote the real outer temporal bounds for the Entity X and Y by the dates X-,X+ and Y-,Y+, where
"-" describes the lower and "+" the upper bound. These are the real narrowest limits, in which the
Temporal Entity occurred, independent from our knowledge about them. The relationships in parenthesis,
like (after), are the inverse ones, i.e. those which we obtain by interchanging X and Y in the definition.

before (after) : X ended at a date before the one when Y started : X+ < Y-

meets in time (met-by in time) : X ended at the date when Y started : X+ = Y-

overlaps in time (overlapped-by in time): X started before Y started, but ended within the duration of Y: X-<Y-, Y-<X+, X+<Y+

during (includes in time):   X started and ended within the duration of Y: Y-<X-, X+<Y+

starts (started-by):     X started with Y but ended before it: X-=Y-, X+<Y+

finishes (finished-by):  X started after Y but ended simultaneously: X-<Y-, X+=Y+

equal in time: X started with Y and ended with Y: X-=Y-, X+=Y+

========================================================

My intuition about cultural documentation practice leaves me when to decide about the application of these relationships
to spatiotemporal cases, or other dimensions of possible specializations of Temporal Entities.
As we have decided not to attach these properties to the associated time spans, there are two possible interpretations:

Given two "bubbles" in Space-Time, like Bronze-Age and Iron-Age, a term like "overlaps in time"
may mean:

1) At any given point in space, at any given settlement, Bronze-Age overlaps more or less Iron-Age.
2) We don't know if at any given point in space, Bronze Age overlaps with Iron-Age, but at least when Iron-Age
    first started in settlement A, Bronze-Age still prevailed in settlement B, and when Bronze Age started, Iron-Age has
   not started anywhere, and before Iron-Age ended in the last settlement, Bronze-Age ended in its last settlement.

Both interpretations are equally valid, but I think one of those must be culturally more relevant, i.e.
closer to the phenomena we regard worthwhile documenting.

If interpretation 1) is the relevant one, the relationship "falls within" of E52 Time-Span is NOT synonymous
with the relationship "during" of the associated Time-Spans, which makes some sense. Another aspect is,
that trivial relationships between known dates need not be expressed by explicit temporal relationships.
Those are only needed for phenomena with nknown absolute dates.

If interpretation 1) is the relevant one, "overlaps","starts","during","finishes" imply spatiotemporal overlap -
in contrast to interpretation 2). This may be wanted. This may make the "pure spatiotemporal overlap"
advocated for in one of my previous messages unnecessary.

If interpretation 1) is the relevant one, "equal" becomes spatiotemporally equal. This may be improbable for
any real case, except the cultural periods of Atlantis starting end ending with its emerging and drowning in the sea...

A slight modification of interpretation 1) may be even more realistic:
At any given point in space, at any given settlement, where both, Bronze-Age and Iron-Age occurred, Bronze-Age
overlaps....

This leaves space for spaces, where the one or the other period did not occurr. This renders a "temporally equal"
different from a "spatiotemporally equal" (or "coocurrent"). Alternatively, "temporally equal" may be defined only
on the associated Time-Spans.

As these operators were required by archeologists, we need a competent comment on this issue.

Martin
--

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 Dr. Martin Doerr              |  Vox:+30(810)391625         |
 Principle Researcher          |  Fax:+30(810)391609         |
 Project Leader SIS            |  Email: martin at ics.forth.gr |
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               Information Systems Laboratory                |
                Institute of Computer Science                |
   Foundation for Research and Technology - Hellas (FORTH)   |
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