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Re: SSN Thread for github issue 378 - Side effects of ssn:Observation being a kind of dul:Event instead of dul:Situation

From: Krzysztof Janowicz <janowicz@ucsb.edu>
Date: Wed, 5 Oct 2016 14:46:42 -0700
To: Joshua Lieberman <jlieberman@tumblingwalls.com>, simon.cox@csiro.au
Cc: kerry.taylor@anu.edu.au, maxime.lefrancois.86@gmail.com, public-sdw-wg@w3.org
Message-ID: <674be479-36c9-c23d-2684-4fcfa68ad3f3@ucsb.edu>
IMHO, /Stimulus/ is best conceptualized as  detectable changes in the 
environment that trigger the observation process. In 2010 (for the SSO) 
Michael and I wrote:

"Stimuli are detectable changes in the environment, i.e., in the 
physical world. They are the starting point of each measurement as they 
act as triggers for sensors. Stimuli can either be directly or 
indirectly related to observable properties and, therefore, to features 
of interest. They can also be actively produced by a sensor to perform 
observations. The same types of stimulus can trigger different kinds of 
sensors and be used to reason about different properties. Nevertheless, 
a stimulus may only be usable as proxy for a specific region of an 
observed property. Examples for stimuli include the expansion of liquids 
or sound waves emitted by a sonar. The expansion of mercury can be used 
to draw conclusions about the temperature of a surface that is in close 
contact. While the expansion is unspecific with respect to the kind of 
surface, e.g., water versus skin, the usage as stimulus is limited by 
its melting and boiling points. Moreover, mercury is not restricted to 
thermometers but e.g., also used in nanometers. Note, that the stimulus 
is the expansion of mercury, not mercury as such."

The last sentence (and assuming this definition is still 
valid/acceptable for our current work), is the most important one. A 
stimulus is an event (if we really, really, really want to use these 
terms). The stimulus also has to start before the observation can take 
place. Multiple possible temporal relations can hold between the two. 
for instance, the mercury in the text above will shrink after an 
measurement procedure (resulting in an observation) is executed. This 
will (or will not) keep triggering a sensor but we stopped caring 
because we arrived at the observation we anted to archive.

I like Josh's idea about predicting future stimuli but would suggest not 
to mix this with the notion of an observation. Predictions about the 
future are not observations in the sense we use in the SSN; if they are, 
they are predictions based on observations which in turn are based on 
stimuli that we consider good proxies for the stimulus we want to 
predict :-).


On 10/03/2016 08:36 PM, Joshua Lieberman wrote:
> I do mean (topologically not logically) disjoint in time, i.e. 
> non-overlapping. If “isPostConditionOf” carries a strict temporal 
> meaning, then it breaks the relationship between stimulus and 
> observation. You can’t measure a temperature if the temperature has 
> gone away before you measure it. If the meaning is only consequential, 
> in the sense of observation O→stimulus S, then it would be a 
> reasonable predicate. Still tricky for prediction, i.e. to assert that 
> a stimulus in the future is a consequence of a prediction in the 
> present. I suppose one could indicate in some way that it's a weaker 
> consequence.
> One could also argue that an observation that overlaps its stimulus in 
> time is a measurement, while an observation that doesn’t overlap its 
> stimulus is a prediction. A model procedure can predict the past, the 
> present, or the future, or none of the above if the model conditions 
> are hypothetical. It is going to require some more thought, though, to 
> figure out how to apply the SSN / O&M terms to this situation. Is a 
> prediction just another procedure within an observation, or is a 
> prediction a different type of event (e.g. a model run) that generates 
> an imaginary / potential observation?
> —Josh
>> On Oct 3, 2016, at 1:31 PM, simon.cox@csiro.au 
>> <mailto:simon.cox@csiro.au> wrote:
>> Weighing in maybe a little late:
>> One of the motivations for the term ‘result’ in O&M was clarification 
>> of the post-condition of the observation, understood as an event.
>> And (as Josh has pointed out) the concepts of phenomenon-time and 
>> result-time were also a part of this story. But O&M also included 
>> interpretation, numerical modelling, and forecasting (i.e. when the 
>> phenomenon-time is later than the result-time), so we need to be 
>> careful here. Perhaps there is a useful taxonomy of observation types 
>> on the basis of the relationship between 
>> stimuls/phenomenon-time/result-time …
>> The notion of ‘stimulus’ was a very important contribution from SSN - 
>> George Percivall was on my case about this early in the story of SWE, 
>> but it didn’t get formalized in the O&M model. But while it is 
>> relatively straightforward how it applies to the classical notion of 
>> sensing, I need some help to understand what the ‘stimulus’ is for a 
>> forecast.
>> Simon
>> *From:*Kerry Taylor [mailto:kerry.taylor@anu.edu.au]
>> *Sent:*Monday, 3 October 2016 5:05 PM
>> *To:*Joshua Lieberman <jlieberman@tumblingwalls.com 
>> <mailto:jlieberman@tumblingwalls.com>>
>> *Cc:*Maxime Lefrançois <maxime.lefrancois.86@gmail.com 
>> <mailto:maxime.lefrancois.86@gmail.com>>; SDW WG Public List 
>> <public-sdw-wg@w3.org <mailto:public-sdw-wg@w3.org>>
>> *Subject:*RE: SSN Thread for github issue 378 - Side effects of 
>> ssn:Observation being a kind of dul:Event instead of dul:Situation
>> Hi Josh,
>> I am not sure I follow – because I am not clear what you mean by 
>> “disjoint” here. For me, I meant it as “something cannot be both of 
>> those things”,
>> but perhaps you mean something about non-overlapping time intervals?
>> If we can’t live with “isPostconditionOf” (and I cannot find any 
>> other alternative in dolce myself, but I would be very grateful if 
>> someone can) then I can see only 3 other options.
>> 1) is to disconnect the observation from the stimulus – which seems 
>> pretty dumb to me and if so then  I would suggest we go even further 
>> and just drop stimulus entirely ( or it could remain connected to a 
>> sensor, but if a sensor could respond to multiple stimuli we would 
>> have no idea which one provoked this observation.  Which gives 
>> another option I suppose – insist that each sensor can have at most 
>> one stimulus and then the stimulus could be retrived with the 
>> observation by following the sensor – but this is yet another change).
>> 2) Make up a new term in ssn for the purpose --- but I am not keen to 
>> introduce new terms without a really strong reason.
>> 3)Make up a new term in the alignment (in a new namespace) but not in 
>> ssn proper --- I can’t see much value in that for anyone.
>> I think I can live with “isPostconditionOf”
>> Maxime, did you spot any other problems with changing observation 
>> this way?
>> --Kerry
>> *From:*Joshua Lieberman [mailto:jlieberman@tumblingwalls.com]
>> *Sent:*Thursday, 29 September 2016 3:59 AM
>> *To:*Kerry Taylor <kerry.taylor@anu.edu.au 
>> <mailto:kerry.taylor@anu.edu.au>>
>> *Cc:*Maxime Lefrançois <maxime.lefrancois.86@gmail.com 
>> <mailto:maxime.lefrancois.86@gmail.com>>; SDW WG Public List 
>> <public-sdw-wg@w3.org <mailto:public-sdw-wg@w3.org>>
>> *Subject:*Re: SSN Thread for github issue 378 - Side effects of 
>> ssn:Observation being a kind of dul:Event instead of dul:Situation
>> This seems to be another consequence of the distinction between 
>> Observation as record and Observation as event. It makes sense that a 
>> record be disjoint with and later in time than a Stimulus (ResultTime 
>> vs PhenomenonTime) but if the event of sensing is disjoint with the 
>> Stimulus being sensed,  there generally isn’t going to be any result. 
>> Therefore, if om:Observation is to be adopted, isPostconditionOf will 
>> not be the appropriate relationship between Stimulus and Observation.
>> —Josh
>>     On Sep 28, 2016, at 9:23 AM, Kerry Taylor
>>     <kerry.taylor@anu.edu.au <mailto:kerry.taylor@anu.edu.au>> wrote:
>>     Maxime,
>>     Thank you so much for following up on this.
>>     isPostconditionOf looks ok to me because
>>     -(1) its rdfs:comment annotation says “ Direct succession applied
>>     to situations.  E.g., 'Taking some rest is a postcondition of my
>>     search for a hotel'.”
>>     -(2) and another reference says  ‘"Direct succession applied to
>>     situations. E.g., 'A postcondition of our Plan is to have things
>>     settled'."”
>>     -(3) it seems to capture the intended relationship between a
>>     stimulus event and an observation. Certainly we would not want
>>     that a stimulus causes an observation, nor that an observation is
>>     a necessary consequence of a stimulus, but I think we are ok
>>     here. It does say that the stimulus comes first, and then the
>>     observation, but that seems quite ok too.
>>     Note that the domain and range of isPostconditionOf are both the
>>     union of Event and Situation, so no problem there. includesEvent
>>      had a range of Event, so this expansion of the range  to Event
>>     or Situation is not going to get existing implementations in to
>>      additional trouble  (ie beyond the trouble already implied by
>>     the descision to change Observation).
>>     It is a subproperty of directlyFollows (an intransitive ordering
>>     relation)  and an inverse of hasPostcondition.  While these may
>>     not have been intended by the original includesEvent (in which
>>     the situation of observation just  includes the Stimulus event),
>>      I cannot see any problem in using isPostconditionOf, and indeed
>>     it looks to me like the difference in meaning is only the
>>     necessary difference that arises to the move of Observation to an
>>     Event.
>>     So I’d vote for isPostconditionOf, being the closest match
>>     possible to the previous.
>>     --Kerry
>>     *From:*Maxime Lefrançois [mailto:maxime.lefrancois.86@gmail.com]
>>     *Sent:*Wednesday, 28 September 2016 6:53 PM
>>     *To:*SDW WG Public List <public-sdw-wg@w3.org
>>     <mailto:public-sdw-wg@w3.org>>
>>     *Subject:*SSN Thread for github issue 378 - Side effects of
>>     ssn:Observation being a kind of dul:Event instead of dul:Situation
>>     Dear all,
>>     If each github issue shall have its own thread on the SDW list,
>>     this is the one for issue 378 -
>>     https://github.com/w3c/sdw/issues/378 :
>>     if|ssn:Observation| <http://www.w3.org/ns/ssn/Observation>is a
>>     kind of|dul:Event|
>>     <http://www.ontologydesignpatterns.org/ont/dul/DUL.owl#Event>instead
>>     of a|dul:Situation|
>>     there is an immediate side effect to resolve:
>>     /axiom:/
>>     |ssn:Observation rdfs:subClassOf [ owl:onProperty
>>     dul:includesEvent ; owl:someValuesFrom ssn:Stimulus ] .|
>>     /context axioms:/
>>     |ssn:Stimulus rdfs:subClassOf dul:Event .|
>>     |dul:includesEvent rdfs:domain dul:Situation ; rdfs:range dul:Event .|
>>     /solution to solve the side effect:/
>>     replace the mention of|dul:includesEvent|in axiom by a property
>>     that has for domain and range|dul:Event|
>>     the only such DUL properties are:|dul:isPreconditionOf|,
>>     and|dul:isPostconditionOf|.
>>     Neither of them seem to fit,
>>     so, should this axiom be simply deleted from the SSN-DUL alignment ?
>>     Kind regards
>>     Maxime Lefrançois

Krzysztof Janowicz

Geography Department, University of California, Santa Barbara
4830 Ellison Hall, Santa Barbara, CA 93106-4060

Email: jano@geog.ucsb.edu
Webpage: http://geog.ucsb.edu/~jano/
Semantic Web Journal: http://www.semantic-web-journal.net
Received on Wednesday, 5 October 2016 21:47:17 UTC

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