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

martin martin at ics.forth.gr
Wed Apr 23 23:08:47 EEST 2014


Hi Vladimir,

The important thing to discuss is what the semantics of "starts" and 
"ends" are.

We adopted Allen's temporal logic, probably prematurely, thinking we 
could rely on
a well received theory. In the meanwhile, it turns out that Allen's 
logic does not work
properly both for fuzzy dates and for incomplete knowledge. There are 
temporal relations
which come from observation, but can only be represented by OR 
combinations of Allen's
relationships. That causes problems in RDF - we need superproperties of 
Allen's to represent
an OR. The other problem is that equality in time can only come from 
numerical declaration
of a date, but not from observation, except if the event is identical.

If we remove exact equality, we can create a set of observable 
relationships purely in time.

Then we can think of more causal relationships.

The meaning of "starts / finishes" in Allen's relationships appears to 
be that of an initial or
final phase. No assumptions about orders or magnitude. We use this to say:
Early Minoan "starts" Minoan, etc. In that case, as you suggested, it 
implies parthood, but not
a "starting" in your sense.

There are other cases, in which the start of a Period is marked by 
scholars by an event, which does not necessarily imply it was the reason 
for what follows, such as the lightning that burned the
palace in Beijing in 1425(?), which was taken as sign of the heaven for 
China to stop exploring the
oceans.

For us most relevant are wars. For instance, the taking of Antioch by 
the Crusaders http://en.wikipedia.org/wiki/Siege_of_Antioch ended the 
muslim rule in the city and started
the new rule. It has a detailed history of its own. The battle cannot 
easily be taken as part of
either period, even though we may have to regard the battle actaully as 
the overlap of both
periods. This proceeds over time through the space of the city itself.

Must any point in the space of a period be reachable by a messenger of 
that time from the start event? (doves!).

If pregnancy starts life of a human, birth can be seen as the end of the 
start of life. We need
clear semantics to decide what "starts" means. Pregnancy is an event for 
the mother and the
embryo.

Before talking about momentary or not start events, let us consider what 
the needs are to
increase the CRM, which is already so big that we loose most of our 
potential customers.

Comments/ ideas welcome!


On 22/4/2014 5:57 μμ, Vladimir Alexiev wrote:
> Steven> We also consider it axiomatic that no event is "momentary": all temporal events have duration.
> Martin> "momentary events" are a fiction of computer science. A basic requirement for the CRM is that it is scale-invariant.
>> There is no smallest granularity for events we could easily point to.
> That's why I put "momentary" in quotes.
> My point is that Birth & Death are (several) orders of magnitude smaller than Life.
> All time-points of Birth must be close to the *begin* points of Life.
> (Birth.P82a & P81a & P82a & P82b must both be close to Life.P82a & P81a)
You wrote:

- Start/End are considered "momentary" events, thus have only 2 points (P81a=P82a, P82b=P81b)
  
This is a misinterpretation I fear. P81a/b may be unknown, but never equal to P82.

>
> It doesn't matter whether you'll consider Birth a momentary event, or daily, or 9-monthly:
> under any reasonable scale assumption (uniformly applied to Birth and Life)), this peculiar relation between Birth and Life will hold.
>
> And this is no coincidence: Birth/Death are the start/end events of Life. From some "cultural-topological" viewpoint:
> - Birth/Death are spatiotemporal points, if Life is a spatiotemporal curve
> - Birth/Death are spatiotemporal spheres, if Life is a spatiotemporal "curved cylinder"
It is exactly this relativity with respect to an arbitrary scale of view 
we forbid in the CRM.
This is a major violation of interoperability.
>
>> Allen relationships have only temporal meaning, they are accidental
> Exactly: currently there's no good way to express the peculiar relation between Birth and Life.
> If the Allen property holds (<Birth> P116_starts <Life>), it does not constrain the *end* points of Birth sufficiently.
> <Life> P116_starts <Life> is just as true (though vacuous) as <Birth> P116_starts <Life>.
>
> Martin> life of a person is one of the candidates for a period with start/end events, but, is it a "Period" or just the spacetime volume of the person?
>
> I'm just digging through CRMgeo, so I know what you mean, and I think it is the spacetime volume.
> And Birth/Death are the start/end of that volume...
> So why in CRM we can talk about the start & end, but we can't talk about the volume as a whole?
> Whereas in CRMdig it's the opposite: we have crmgeo:SP8_Spacetime_Volume but we cannot talk about its start/end points.
Well, the semantic question is if "life" is the total of one's actions 
and events suffered, or just where
the body and the limbs are.
>
> Do volumes have innate start & end? Well surely Time-Spans do.
Surely not! The beginning of a time span is not a process in the sense 
of physics. Declared
time points are not events in the CRM. The validity time of laws has not 
yet been in our practical scope.
>
> Steven> we have taken the design approach of not modelling condition states as they tend to lead to monotonicity problems
>> when combining different data streams...
>> it is always better to calculate at query time what the current state of knowledge indicates is the period that a state existed.
> Martin> The problem with states, such as "period of use" is the open world semantics: What is actually observed knowledge, and what is inference?
>
> I feel like I should be able to grok what this means, but I am not able to.
> Could you please give an example?
The idea is, if you know about two state transitions A->B, B->A, you may 
infer B holds in between.
If you replace these events with the state B, and then you learn that 
there was another pair in between, B->A, A-> B, , hence you have to 
delete state B, introduce B1, A, B2, even though, no
contradictory knowledge was encountered. This is "non-monotonic". This 
must not happen, because
we cannot easily decide in a semantic network if the state was observed 
or inferred. This is why
in the CRM we do not want to model the inferred states, but leave it to 
the application. For data transfer, inferred knowledge must be removed. 
We use shortcuts only, when there is a strong practice of representing 
the shortcut only, and the implied events are either too unclear or 
unlikely to have an essential role in the cultural-historical discourse. 
Shortcuts are not the states in between, they are timeless properties.
>
>> See the CRM Sci extension just published on the CRM site for a definition of states
> Ah, maybe I can read it during the St George's holidays :-)
>
> Dominic> The moment that we start to talk about, "there is no standard way" or it would be "more economical", alarm bells are raised.
>> tendency to provide a one-dimensional approach prioritising optimisation, performance and ultimately superficially
>> over representing knowledge as validly as possible
> Well, let's see:
>
> 1. CRM has:
> <monarchs> P107_has_current_or_former_member <George_of_Saxony>
>
> 2. I propose eg:
> <George_of_Saxony/reign> a E102_Membership;
>    P201i_is_membership_of <George_of_Saxony>;
>    P202i_is_membership_of <monarchs>.
>
> 3. CRM has:
> <George_of_Saxony/ascension> a E85_Joining;
>    P143_joined <George_of_Saxony>;
>    P144_joined_with <monarchs>.
> <George_of_Saxony/death> a E86_Leaving;
>    P145_separated <George_of_Saxony>;
>    P146_separated_from <monarchs>;
>
> My proposal is an intermediate level of detail between what already exists in CRM.
> Seems to me that I'm covered on both ends ;-): neither too simple, nor too complex.
>
> In your view, are all CRM shortcuts a bad thing? Or only the ones that I'm proposing?
>
>> The CRM has been developed precisely to support the fact that you cannot make sweeping assumptions across it
> What is the sweeping assumption that I am making?
> On the contrary, I would call your reply a sweeping generalization.
>
>
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