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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: Kerry Taylor <kerry.taylor@anu.edu.au>
Date: Sat, 8 Oct 2016 12:04:56 +0000
To: "janowicz@ucsb.edu" <janowicz@ucsb.edu>, Joshua Lieberman <jlieberman@tumblingwalls.com>, "simon.cox@csiro.au" <simon.cox@csiro.au>
CC: "maxime.lefrancois.86@gmail.com" <maxime.lefrancois.86@gmail.com>, "public-sdw-wg@w3.org" <public-sdw-wg@w3.org>
Message-ID: <PS1PR06MB17408960F54AC7624A63CEEDA4D90@PS1PR06MB1740.apcprd06.prod.outlook.com>
So  let’s try to resolve this. Unless someone seriously proposes  to reconsider the decision to redefine ssn:Observation that was taken in Lisbon, we really need to re-connect ssn:observation to ssn:stimulus.

As Krzystof notes “Predictions about the future are not observations in the sense we use in the SSN”.  I agree. Let’s not go there. However if an O&M observation can be a prediction are we obliged to go there?

Josh is worried about “If “isPostConditionOf” carries a strict temporal meaning”. I don’t think it does. I would interpret the dolce temporal
relationship to be quite loose, although it is “direct succession” and it is  a subproperty of “ directlyFollows”.  I think it juist means something like “and the next thing that happens is…”.  But I do not find any reason to think that overlapping temporal periods are excluded--- and if someone wants to do real reasoning on time intervals they use owl:time where it is very clear!

Noting also Krzysztof’s use of “observation” in the previous email “will shrink after an measurement procedure (resulting in an observation) is executed.”
Very much an entity!

Maxime also noted consequences  to the ssn-prov alignment  --- and yes, indeed there are consequences—anyone using a prov alignment based on ssn:observation being a situation, as it is currently defined,  will be stuffed by this change (Maxime – are you using this one?[1]). I know it is affected, and certainly ssn:Observation with have to be changed to being a prov:Activity, but I have not yet reviewed to see how much of a problem that is. Maxime, if you are actively working in this space – could you kindly check?).  Just as anyone who has been  using the relevant dul: parts of  ssn is also stuffed.    I certainly hope that does not put us in a position that we are forced to “use the SSN version without PROV” . That is untenable!

Believing that is solvable, I propose again that  we use
dul:isPostconditionOf to replace dul:includesEvent.

I will put this on the ssn agenda for resolution this week unless I see major objections from the list (esp. from someone who cannot attend the ssn meeting).


[1] http://ceur-ws.org/Vol-1401/paper-05.pdf

From: Krzysztof Janowicz [mailto:janowicz@ucsb.edu]
Sent: Thursday, 6 October 2016 8:47 AM
To: Joshua Lieberman <jlieberman@tumblingwalls.com>; simon.cox@csiro.au
Cc: Kerry Taylor <kerry.taylor@anu.edu.au>; maxime.lefrancois.86@gmail.com; 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

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?


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.


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?


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.


On Sep 28, 2016, at 9:23 AM, Kerry Taylor <kerry.taylor@anu.edu.au<mailto:kerry.taylor@anu.edu.au>> wrote:


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.


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:

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 rangedul: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<mailto:jano@geog.ucsb.edu>

Webpage: http://geog.ucsb.edu/~jano/

Semantic Web Journal: http://www.semantic-web-journal.net

Received on Saturday, 8 October 2016 12:05:37 UTC

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