stat:attribute references what type of object

[pvgenuchten]

From the specification i was not able to understand what type of object is referenced by the uri as content of stat:attribute.

I read: "If a Distribution is expressed in some other format (e.g. SDMX), the values for the properties stat:attribute and stat:dimension can be extracted from corresponding elements in that format if such elements exist"

It seems the specification leaves it open which ontology to adopt when defining a stat:attribute, is that correct?
Or there is a strong preference for sdmx