Dimension vector for quantitykind:Viscosity

[mgberg]

qudt-public-repo/vocab/quantitykinds/VOCAB_QUDT-QUANTITY-KINDS-ALL-v2.1.ttl

Lines 17479 to 17485 in be1e575

	quantitykind:Viscosity
	a qudt:QuantityKind ;
	qudt:dbpediaMatch "http://dbpedia.org/resource/Viscosity"^^xsd:anyURI ;
	qudt:plainTextDescription "Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or extensional stress. In general terms it is the resistance of a liquid to flow, or its \"thickness\". Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. [Wikipedia]" ;
	rdfs:isDefinedBy <http://qudt.org/2.1/vocab/quantitykind> ;
	rdfs:label "Viscosity"@en ;
	.

quantitykind:Viscosity has no dimension vector. Note that:

• quantitykind:DynamicViscosity and quantitykind:MolecularViscosity are both narrower than quantitykind:Viscosity
• quantitykind:MolecularViscosity currently doesn't have a dimension vector
• quantitykind:KinematicViscosity is not currently narrower than quantitykind:Viscosity and does not have the same dimension vector as quantitykind:DynamicViscosity.

Given that broader quantity kinds should have the same dimensionality, what should be done about quantitykind:Viscosity? It seems that it can't have a dimension vector and also be broader than quantitykind:KinematicViscosity.

[steveraysteveray]

Viscosity is indeed our illustrative example of the case where a skos:broader concept is an abstraction of several other quantity kinds with dissimilar dimension vectors. Our policy is to have no dimension vector for abstract quantity kinds like this. (I note that MolecularViscosity still needs a dimension vector, which I currently believe is the same as DynamicViscosity). Willing to be convinced otherwise, though!

[mgberg]

@steveraysteveray Just thought of a follow-up question about this. The class qudt:AbstractQuantityKind exists; how is that class intended to be used, and should quantitykind:Viscosity be explicitly an instance of that instead of qudt:QuantityKind?

[steveraysteveray]

Good old semantics. You just made me realize that we use the word "abstract" in two ways.

1. Here is a class that should not be instantiated
2. Here is a superclass placeholder to put a bunch of properties that will be inherited by the subclasses

qudt:AbstractQuantityKind falls into the second category and contains a bunch of additional properties.

You've got me thinking, though, as to whether we should consider refactoring those classes so that qudt:AbstractQuantityKind could satisfy both of the above cases. It might be good to be more explicit about when a quantity kind is an "abstraction" of several subclasses with different dimension vectors, beyond just not listing a dimension vector.

So stay tuned... and thanks!