I am currently trying to find out what meaning they want to tell me with the Crop Ontology and in the process learn something about Ontologies and OWL (I’m quite new to this topic). In there, owl:someValuesFrom restriction is used a lot to link terms together by some relationship like method_of, scale_of. I do not see why they do not just link classes by object properties.

As a concrete example, I have added an excerpt of the Crop Ontology for Rice. Please help me understand what kind of meaning I would communicate if I would just link the mentioned classes by object properties. I have attached below my research attempts and excerpts from the Rice Ontology

The OWL help page says about those restrictions:

n other words, it defines a class of individuals x for which there is at least one y (either an instance of the class description or value of the data range) such that the pair (x,y) is an instance of P.

…which I cannot really understand. A Stack Overflow search for “OWL sameValueAs object property” did not yield any results.

In the excerpt, the Rice Ontology defines roughly:

• Method -> … -> Yield measurement
• Trait -> … -> Grain yield
• Variable -> … -> GrYld_Comp_kgha¹
• Scale -> … -> kg_per_ha

^{1 probably a Computation/Extrapolation from other yield parameters, from harvest of a small plot}

and

• kg_per_ha -[scale_of]-> Yield measurement -[method_of]-> Grain yield
• GrYld_Comp_kgha -[variable_of]-> { Grain yield, Yield measurement, kg_per_ha }

Initial definitions

@prefix : <https://cropontology.org/rdf/> .
@prefix prl: <http://purl.org/dc/terms/> .
@prefix skos: <http://www.w3.org/2004/02/skos/core#> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@base <https://cropontology.org/rdf/> .


:Method         rdf:type owl:Class .            ## <https://cropontology.org/rdf/Method>
:Computation    rdf:type owl:Class ;     ## <https://cropontology.org/rdf/Computation>
    rdfs:subClassOf :Method .

:Scale          rdf:type owl:Class .            ## <https://cropontology.org/rdf/Scale>
:Numerical  rdf:type owl:Class ;    ## <https://cropontology.org/rdf/Numerical>
    rdfs:subClassOf :Scale .

:Trait          rdf:type owl:Class .
:Agronomic rdf:type owl:Class ;
    rdfs:subClassOf :Trait .

:Variable       rdf:type owl:Class .            ## <https://cropontology.org/rdf/Variable>

:scale_of       rdf:type owl:ObjectProperty .   ## <https://cropontology.org/rdf/scale_of>
:variable_of    rdf:type owl:ObjectProperty .   ## <https://cropontology.org/rdf/variable_of>

:Grain_yield    rdf:type owl:Class ;   ## <https://cropontology.org/rdf/CO_320:0000073> 
    rdfs:subClassOf :Agronomic ;
    skos:definition "Amount of grain (weight) produced per area"@en ;
    

Definition of Grain_yield, Yield_measurement and GrYld_Comp_kgha using restrictions

:Yield_measurement  rdf:type owl:Class ;   ## <https://cropontology.org/rdf/CO_320:0000469> 
    rdfs:subClassOf :Computation ,
    [ 
        rdf:type owl:Restriction ;
        owl:onProperty :method_of ;
        owl:someValuesFrom :Grain_yield
    ] ;
    rdfs:label "Yield measurement"@en ;
    skos:definition "Harvest grain from at least 5 m2/plot, discarding at least three border rows. Thresh, dry the rough (paddy) rice to 14% moisture content, and weigh."@en .

 
:kg_per_ha  rdf:type owl:Class ;     ###  https://cropontology.org/rdf/CO_320:0000470
    rdfs:subClassOf :Numerical ,
    [ 
        rdf:type owl:Restriction ;
        owl:onProperty :scale_of ;
        owl:someValuesFrom :Yield_measurement
    ] ;
rdfs:label "kg per ha"@en .


:GrYld_Comp_kgha    rdf:type owl:Class ;  ## <https://cropontology.org/rdf/CO_320:0000745>
    rdfs:subClassOf :Variable ,
    [ rdf:type owl:Restriction ;
        owl:onProperty :variable_of ;
        owl:someValuesFrom :Grain_yield .
    ] ,
    [ rdf:type owl:Restriction ;
        owl:onProperty :variable_of ;
        owl:someValuesFrom :Yield_measurement 
    ] ,
    [ rdf:type owl:Restriction ;
        owl:onProperty :variable_of ;
        owl:someValuesFrom :kg_per_ha .
    ] ;
    prl:contributor "IRRI" , "Jeffrey Detras" ;
    rdfs:label "GrYld_Comp_kgha"@en ;
    skos:altLabel "GrYld_Comp_kgha"@en .

Why can’t I just do instead:

:Yield_measurement  rdf:type owl:Class ;  
    rdfs:subClassOf :Computation ;
    :method_of :Grain_yield; 
    skos:definition "Harvest grain from at least 5 m2/plot, discarding at least three border rows. Thresh, dry the rough (paddy) rice to 14% moisture content, and weigh."@en .

kg_per_ha   rdf:type owl:Class ;    
    rdfs:subClassOf :Numerical  ;
    :scale_of :Yield_measurement; 
rdfs:label "kg per ha"@en .

:GrYld_Comp_kgha    rdf:type owl:Class ;
    rdfs:subClassOf :Variable ,
    :variable_of :Grain_yield,
                 :Yield_measurement,
                 :kg_per_ha ;
    rdfs:label "GrYld_Comp_kgha"@en .