RE: Comments on the SOSA and SSN implementations

Dear Raul,

As an ontology outsider, let me express my view on a couple of your points:

1. UoM. Attaching the unit of measurement to a sosa:Result seems reasonable. We do it all the time when quoting results ("I am 1.85m and 85Kg before Christmas")

2. Some results properly have a duration not just an instant ("The average daytime temperature tomorrow will be 11 deg C", "The aviation QNH pressure altimeter setting for the next 6 hours, issued at 2016-12-14T17:05Z, is 1005.5 hPa). They may also have several associated times.

How these influence the content of sosa and ssn I leave to you, the experts.

Chris 


-----Original Message-----
From: Raúl García Castro [mailto:rgarcia@fi.upm.es] 
Sent: Wednesday, December 14, 2016 4:31 PM
To: public-sdw-wg@w3.org
Subject: Comments on the SOSA and SSN implementations

Dear all,

I've been reviewing the implementations of SOSA and SSN and here you have some comments (plus a couple of pull requests) on each of them and on the combination.

SOSA
----

* sosa:Platform
The documentation says "(including rdf:type rdfs:Class, owl:Class humans)", should this be "(including humans)"?

* sosa:Sample
 From the documentation, a Sample is a FeatureOfInterest (shouldn't Sample be a subclass of FeatureOfInterest?). I also think that there is no need for a Sample class; I would just state that a FeatureOfInterest can have as a sample another FeatureOfInterest. In any case, unless some of these changes are made, the current model "does not allow" taking samples of samples.

* sosa:hasValue
Why not including meta:domainIncludes sosa:Result in this property?

* Units of measurement
Also, regarding values, I think that right now the ontology falls short on supporting how to describe them when they require a unit of measurement. Along the documentation plenty of examples are included that mention a unit of measurement (e.g., "20m") but in the documentation of sosa:hasValue it only appears "23 or true", without mentioning the unit anymore. Since sosa:hasValue is a datatype property, do we expect people to attach the unit of measurement to a sosa:Result?

* sosa:hosts
The documentation mentions a SamplingDevice that is not mentioned in the ontology.

* sosa:madeObservation
Why is the inverse observedBy property not defined?

* sosa:phenomenonTime and sosa:resultTime I would remove these properties from SOSA, mainly because I think that they aim for a richer level of detail than the other concept descriptions in the ontology.
Having them inside is no main problem, but then their definition is quite weird since one is defined as an object property and the other as a datatype property. I understand why they have been defined that way, but it is not elegant.
On the one hand, in sosa:phenomenonTime we talk about time intervals and instants; we have here an opportunity to link to the W3C Time ontology, and even talk about TemporalEntities?
On the other hand, in sosa:resultTime we talk about xsd:dateTime (being the only property in the ontology that specifies a rdfs:range); to be coherent we should talk about time instants.

* Importing SKOS
I would move the last triples defining the SOSA ontology to the beginning. Related to these, why do we need to import SKOS?

SSN
---

* ssn:startTime and ssn:endTime
They are not documented in the ontology with rdfs:comment (it happens in others such as observedBy). And the link that appears in the description is "broken" (http://www.w3.org/2005/Incubator/ssn/wiki/SSN_Base#Time). 
They are not used in any of the other entities in the ontology; should we remove them?

* dul:includesEvent
The dul:includesEvent property has dissapeared and the local restriction that relates an Observation to a Stimulus has dissapeared to.
Maybe it has been made in purpose, but the possibility of relating those two classes is not there anymore.

* ssn:SensorDataSheet
This class is not related to other classes or properties in the model. 
Should we remove it or relate it?

SSN+SOSA
--------

Taking the SSN ontology as it is (in GitHub) and SOSA, right now it cannot be said that one is a core module of the other, since:
  -  SSN does not reuse SOSA vocabulary terms (this could be implemented by mappings)
  - SOSA adds actuation and sampling
  - SOSA renames plenty of classes and properties. In some cases maybe the intended meaning is more or less equivalent, but in others it radically changes (for example, ssn:hasValue is an object property and sosa:hasValue is a datatype property).
  - The modelling decisions in both are different; for example, in SOSA a Sensor is hosted by a Platform, in SSN a SensingDevice (not a Sensor) is on a Platform.

The result is that currently we don't have a clean view on the ontology as a whole as a composition of modules. And for anyone using the ontology it will be quite difficult to digest everything (e.g., there are 2 time-related properties in SOSA attached to an observation, in SSN there are another 2 attached to an observation and 2 that are not attached to anything.

In other words, my opinion is that right now SOSA is something derived from SSN but we still have plenty of work to do (either changing SOSA, SSN, or both) to put them together so it can be considered a proper core module.

If not, the risk is to produce two different (even if compatible) ontologies which is not desirable for interoperability.

In other (now more positive) words, I think that SOSA is the result of a very good work, and I'd like it to be a proper core part of SSN.
Let's see how we can do it!

Kind regards,

-- 

Dr. Raúl García Castro
http://www.garcia-castro.com/


Ontology Engineering Group
Departamento de Inteligencia Artificial
Escuela Técnica Superior de Ingenieros Informáticos Universidad Politécnica de Madrid Campus de Montegancedo, s/n - Boadilla del Monte - 28660 Madrid
Phone: +34 91 336 65 96 - Fax: +34 91 352 48 19

Received on Wednesday, 14 December 2016 17:04:41 UTC