confusion unit vs hasUnit; mention value in QuantityValue; give skos:example

[VladimirAlexiev]

@steveraysteveray
I'm working with CIM ontologies and want to state the Unit and QuantityKind for some electrical DatatypeProperties (see at end of this description).
Related to Sveino/Inst4CIM-KG#38.

Quantifiable and QuantityValue have 4 restrictions that mention unit and hasUnit:

qudt:QuantityValue
  a owl:Class ;
  rdfs:subClassOf qudt:Concept ;
  rdfs:subClassOf qudt:Quantifiable ;
  rdfs:subClassOf [
      a owl:Restriction ;
      owl:maxCardinality 1 ;
      owl:onProperty qudt:hasUnit ;
    ] ;
  rdfs:subClassOf [
      a owl:Restriction ;
      owl:maxCardinality 1 ;
      owl:onProperty qudt:unit ;
    ] ;
.

But:

• qudt:unit is deprecated
• qudt:hasUnit has no domain but is defined as "This property relates a system of units..."

So which one should be used? I don't know the story why qudt:unit was deprecated, but let's honor this:

• change the definition of qudt:hasUnit to mention Quantifiable and also numeric properties (when the unit is fixed)
• add a definition to qudt:hasQuantityKind and mention it can be used with .... and numeric properties (when the quantity kind is fixed)
• remove unit from any and all Restrictions (if it's deprecated then it should not be used)
• add a restriction to QuantityValue to mention qudt:value (such is present in Quantifiable)
• add the following in qudt:hasUnit and qudt:hasQuantityKind

skos:scopeNote """Can be used as annotation on a numeric property when that property uses a fixed QuantityKind/Unit.
E.g. in the electrical CIM property example:
- the kind is fixed to an electrical modification of `ComplexPower`
- the unit is fixed to Mega Volt-Amperes
- (the unit and multiplier are also given separately: this is a peculiarity of electrical CIM)
""";
skos:example """
cim:ACDCConverter.baseS a owl:FunctionalProperty , owl:DatatypeProperty ;
  rdfs:domain cim:ACDCConverter ;
  rdfs:range xsd:float ;
  qudt:hasQuantityKind cim:ApparentPower;
  qudt:hasUnit unit:MegaV-A;
  cims:multiplier cim:UnitMultiplier.M;
  cims:unitSymbol cim:UnitSymbol.VA.
""".

Of course, you can cut out the last two lines (and the parenthesized bullet that explains them).
Or if the example is too big/complex/specific, make up some datatype property.

[steveraysteveray]

Comments received. I think I have good answers for you for some of the items, and your suggestions deserve some thought. I will get to them after finishing some other urgent tasks.

[VladimirAlexiev]

Please ping me if my skos:example is incorrect or inaccurate.

[steveraysteveray]

Starting to address your questions:

qudt:unit was deprecated in favor of qudt:hasUnit to be consistent with other relations like qudt:hasQuantityKind. This was brought up by the ASHRAE 223 committee. I agree that we should clean out any uses of qudt:unit from both the OWL and SHACL schemas. I have made a note to do that.

Regarding the domain of hasUnit, you are correct. We combined the uses of qudt:unit and qudt:hasUnit such that the remaining relation qudt:hasUnit is used by a variety of classes, (SystemsOf..., Quantifiable, QuantityValue).

I'm a bit unclear what you mean when you talk about numeric properties. Could you expand or give an example?

qudt:QuantityValue is a rdfs:subClassOf qudt:Quantifiable, so it doesn't need to mention qudt:value.

Your last comment involves what you are calling a numeric property, so when I understand what you mean there, I'll be able to comment on your suggested code.

Hopefully my responses get us at least part of the way to resolving these issues.

[VladimirAlexiev]

hi @steveraysteveray !
By "numeric property" I mean a datatype property whose value is a number, but it also wants to specify fixed quantityKind and unit so that:

• we can be explicit about the meaning of the value
• instance data doesn't need to be burdened with quantityKind and unit information (think billions of data points)

Eg in electrical CIM/CGMES, currently all units are fixed. So we want to use annotations like this:

cim:ACDCConverter.baseS a owl:FunctionalProperty , owl:DatatypeProperty ;
  rdfs:domain cim:ACDCConverter ;
  rdfs:range xsd:float ;  # pure number!
  cims:multiplier cim:UnitMultiplier.M;  # this was present in CIM, but in a different form
  cims:unitSymbol cim:UnitSymbol.VA.  # this was present in CIM, but in a different form
  qudt:hasQuantityKind cim:ApparentPower; # this CIM qk has a link to QUDT
  qudt:hasUnit unit:MegaV-A; # this QUDT unit is mapped from multiplier & unitSymbol

See:

• https://github.com/Sveino/Inst4CIM-KG/blob/develop/rdfs-improved/README.md#quantitykinds-and-units-of-measure for the gory details
• https://github.com/Sveino/Inst4CIM-KG/blob/develop/rdfs-improved/README.md#fixed-units-representation for the new representation
• https://github.com/Sveino/Inst4CIM-KG/blob/develop/rdfs-improved/README.md#mapping-quantitykinds-and-units for mapping between CIM and QUDT