on-obs.md

Materializing Populations onto Observations

The obvious (and from a modelling perspective correct) place to materialise the classes of statistical populations is onto the observations themselves.

This can be achieved through owl property restrictions.

As a datacube uses skos:Concept's to describe codes, and concepts are instances not classes, we first need a way to lift these individuals into classes. As we do so we can materialise those classes onto the observation itself with property restriction like:

:Male owl:equivalentClass [
        a owl:Restriction ;
        owl:onProperty :gender;
        owl:hasValue :male] .

This lifts the :male concept into a class :Male, that exists on the domain of the :gender qb:DimensionProperty, i.e. here we materialise the class :Male on obervations that have a :gender dimension pointing to the :male concept.

In and of itself this doesn't achieve much, it simply allows a query like:

SELECT ?obs WHERE {
   ?obs :gender :male .
}

to be written as:

SELECT ?obs WHERE {
   ?obs a :Male .
}

PROs

However it does allow us to coin a class for skos concepts, and do so on the observation which is the individual instance that describes the statistical population and gives it a number. So from a modelling perspective it makes a lot of sense.

Cons

The downside of this approach is that it requires a restriction to be created for each distinct dimension value in the DSD. Also materialising classes onto observations will be both very noisy, and also very expensive as Observations are the most numerous instance we have.