RE: units of measure - was RE: Comments on the SOSA and SSN implementations

Yes – agree that UoM is out of scope for SDWWG and SSN. It is a much more general issue – arguably it is a fundamental gap in almost all programming languages and libraries. A reasonable case can be made that there are almost no floats, doubles or decimals in the real world that should not be accompanied by a scaling factor (to turn them into amounts or quantities). There are a few dimensionless quantities in physics, but even those require some annotation to make them comprehensible.

When I was editor of ISO O&M there was a push from outside the project team for UoM to be added to the scope of ISO 19156.
The appearance of the word ‘Measurements’ in the title of O&M triggered this (which is itself really a hangover from the early history of that project), but we decided to keep the scope of O&M narrow – property-value-estimation activities + sampling. If we were starting again I’d probably suggest calling it O&S (observations & sampling).

Simon

From: Kerry Taylor [mailto:kerry.taylor@anu.edu.au]
Sent: Friday, 3 February, 2017 01:16
To: Maxime Lefrançois <maxime.lefrancois@emse.fr>; Cox, Simon (L&W, Clayton) <Simon.Cox@csiro.au>; andrea.perego@jrc.ec.europa.eu; rgarcia@fi.upm.es
Cc: public-sdw-wg@w3.org
Subject: RE: units of measure - was RE: Comments on the SOSA and SSN implementations

+1  and this was the same choice made by ssn for the same reason.  Although  I think we should be helpful  and suggest ways of doing this (ie examples of using it with popular UoM ontologies) . This is really the job of the “primer’ we were to write, but at this point I think the “primer” will be postponed to the follow on SDW Activity that is being mooted.

From: Maxime Lefrançois [mailto:maxime.lefrancois@emse.fr]
Sent: Thursday, 2 February 2017 11:27 PM
To: Simon.Cox@csiro.au<mailto:Simon.Cox@csiro.au>; andrea.perego@jrc.ec.europa.eu<mailto:andrea.perego@jrc.ec.europa.eu>; rgarcia@fi.upm.es<mailto:rgarcia@fi.upm.es>
Cc: public-sdw-wg@w3.org<mailto:public-sdw-wg@w3.org>
Subject: Re: units of measure - was RE: Comments on the SOSA and SSN implementations

Dear all,

There exists numerous ways to encode quality values, quantity values, their units of measures. Existing solutions include ontologies (QUDT, OM, ...), and the use of some custom datatypes [1]. As it has been noted in some mails, QUDT is evolving, so is OM, and I expect some new solutions directly based on UCUM to be proposed soon.

This is not part of the SDW charter, and I strongly believe it should be carefully left out of the scope of the SSN REC document. I don't believe SDW is legitimate in encouraging one solution or another, especially since these solutions are not W3C REC themselves. There potentially may be a future W3C group that could work on this specific topic.

I would like to draw you attention on how we dealt with this point in the ITEA2 SEAS project deliverable D2.2 where the SEAS Knowledge Model is defined [2].
Section 4.2 defines the core module EvaluationOntology [3], which describes how we practically model the attribution of a value to a property.

In a nutshell, we leave the choice to the users of the SEAS ontologies.

[1] - Maxime Lefrançois, Antoine Zimmermann, Supporting Arbitrary Custom Datatypes in RDF and SPARQL, In Proc. Extended Semantic Web Conference, ESWC, May 2016, Heraklion, Crete, Greece
[2] - http://www.maxime-lefrancois.info/docs/SEAS-D2_2-SEAS-Knowledge-Model.pdf

[3] - https://w3id.org/seas/EvaluationOntology


Kind regards,
Maxime Lefrançois
http://maxime-lefrancois.info/


Le ven. 16 déc. 2016 à 00:20, <Simon.Cox@csiro.au<mailto:Simon.Cox@csiro.au>> a écrit :
Hi Andrea -

Thanks for pointing that out. Looks like

dqv:value rdfs:equivalentProperty oml:amount .
sdmx-attribute:unitMeasure rdfs:equivalentProperty oml:uom .

We could re-use, or at least assert this alignment in a mapping graph somewhere.

But it also looks like DQV (like QUDT) binds the scaled number to a quantity-type (using dqv:isMeasurementOf).
That is a variation from SSN/SOSA/O&M, where the quantity-type is not bound to the result but is implied by the value of 'observedProperty'.
SSN/SOSA/O&M also focus on the act-of-observation and a link to or description of the procedure used (not shown in your dqv example).

Simon

-----Original Message-----
From: Andrea Perego [mailto:andrea.perego@jrc.ec.europa.eu<mailto:andrea.perego@jrc.ec.europa.eu>]
Sent: Thursday, 15 December, 2016 19:30
To: Cox, Simon (L&W, Clayton) <Simon.Cox@csiro.au<mailto:Simon.Cox@csiro.au>>; rgarcia@fi.upm.es<mailto:rgarcia@fi.upm.es>
Cc: public-sdw-wg@w3.org<mailto:public-sdw-wg@w3.org>
Subject: Re: units of measure - was RE: Comments on the SOSA and SSN implementations

Simon, all,

About units of measure, I wonder whether we should also take into account how this is modelled in DQV.

As said in an earlier thread [1], DQV does not actually defines explicitly how to this, but they use a consistent approach in their examples [2], by using dqv:value + sdmx-attribute:unitMeasure. E.g.:


:myDataset a dcat:Dataset ;
     dqv:hasQualityMeasurement :myDatasetPrecision, :myDatasetAccuracy .

:myDatasetPrecision a dqv:QualityMeasurement ;
    dqv:isMeasurementOf :spatialResolutionAsDistance ;
    dqv:value "1000"^^xsd:decimal ;
    sdmx-attribute:unitMeasure
<http://www.wurvoc.org/vocabularies/om-1.8/metre> .

:spatialResolutionAsDistance  a  dqv:Metric;
     skos:definition "Spatial resolution of a dataset expressed as distance"@en ;
     dqv:expectedDataType xsd:decimal ;
     dqv:inDimension dqv:precision .


I'm not saying this must be adopted in SSN (unless it satisfies SSN
requirements, of course), but I think it is important to clarify when
the different approaches should be used, and to explain whether/how they
are interoperable or not (e.g., through mappings).

If we are going to have two different ways of modelling this piece of
information, adopters may be unsure which one they should use. So, some
guidance may help their consistent implementation.

Thanks

Andrea

---
[1]https://lists.w3.org/Archives/Public/public-sdw-wg/2016Sep/0084.html

[2]https://www.w3.org/TR/vocab-dqv/#ExpressDatasetAccuracyPrecision



On 15/12/2016 3:00, Simon.Cox@csiro.au<mailto:Simon.Cox@csiro.au> wrote:
>> * 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?
>
>
> I believe that the original SSN relied on dul:Region as a super-class that includes things that can be represented as scaled numbers, but didn't go into details.
>
>
> In om-lite (http://www.semantic-web-journal.net/content/ontology-observations-and-sampling-features-alignments-existing-models-0 and http://def.seegrid.csiro.au/ontology/om/om-lite ) we included the
> - MeasureObject - as a generic/abstract class for scaled values - http://def.seegrid.csiro.au/ontology/om/om-lite#MeasureObject

> - SimpleMeasure - as convenient minimal representation option - http://def.seegrid.csiro.au/ontology/om/om-lite#SimpleMeasure

>
> For om-lite there is a small set of examples here:
> https://www.seegrid.csiro.au/subversion/xmml/ontologies/trunk/O&M-OWL/examples.ttl

> In here you can find the following:
>
> ...
>   oml:result [
>       rdf:type oml:MeasureObject ;
>       oml:uom <http://qudt.org/vocab/unit#Kilogram> ;
>       rdf:value "0.28"^^xsd:double ;
>     ] ;
> ...
>
> ...
>   oml:result [
>       rdf:type oml:SimpleMeasure ;
>       oml:amount "0.28"^^xsd:double ;
>       oml:uom <http://www.opengis.net/def/uom/UCUM/0/kg> ;
>     ] ;
> ...
>
> ...
>   samfl:size [
>       rdf:type oml:SimpleMeasure ;
>       oml:amount "0.46"^^xsd:double ;
>       oml:uom <http://qudt.org/vocab/unit#Kilogram> ;
>     ] ;
> ...
>
> I am certainly not proposing that this is the only solution, but provides a bit of a framework to work with.
>
> Simon
>
>
> -----Original Message-----
> From: Raúl García Castro [mailto:rgarcia@fi.upm.es<mailto:rgarcia@fi.upm.es>]
> Sent: Thursday, 15 December, 2016 03:31
> To: public-sdw-wg@w3.org<mailto: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,
>

--
Andrea Perego, Ph.D.
Scientific / Technical Project Officer
European Commission DG JRC
Directorate B - Growth and Innovation
Unit B6 - Digital Economy
Via E. Fermi, 2749 - TP 262
21027 Ispra VA, Italy

https://ec.europa.eu/jrc/


----
The views expressed are purely those of the writer and may
not in any circumstances be regarded as stating an official
position of the European Commission.