Example 4: Relators and extrinsic aspects

The roles a relator connects

A relator mediates entities playing roles -- here, the same :Employee and :Employer roles that would be declared exactly as in example 1:

:Employee a owl:Class , gufo:Role ; rdfs:subClassOf :Person .
:Employer a owl:Class , gufo:Role ; rdfs:subClassOf :Organization .

The relator itself, and sub-properties of gufo:mediates

:Employment is declared a gufo:Relator. Two sub-properties of gufo:mediates, one per side, let the data distinguish which mediated party plays which role -- important once a relator connects more than two parties, or connects parties of the same kind on both sides:

:Employment rdfs:subClassOf gufo:Relator .

:involvesEmployee rdfs:subPropertyOf gufo:mediates ;
    rdfs:domain :Employment ; rdfs:range :Employee .
:involvesEmployer rdfs:subPropertyOf gufo:mediates ;
    rdfs:domain :Employment ; rdfs:range :Employer .

:DanaGlobexEmployment a :Employment ;
    :involvesEmployee :Dana ;
    :involvesEmployer :GlobexCorp ;
    gufo:hasBeginPointInXSDDate "2020-01-06"^^xsd:date .

gUFO itself requires every gufo:Relator to mediate at least two endurants (a qualified cardinality restriction on gufo:mediates) -- one reason a DL reasoner would in fact reject a relator individual asserted to mediate fewer than two things, unlike the sortality mistakes in example 1, which OWL cannot see at all.

Decomposing the relator into rights and duties

A relator can be more than an opaque link: gUFO lets you reveal the reciprocal gufo:ExtrinsicModes it is made of -- a right on one side is matched by a duty on the other, each inhering in one party and externally depending on the other, and each declared a proper part of the relator via gufo:isAspectProperPartOf:

:RightToSalary rdfs:subClassOf gufo:ExtrinsicMode .
:DutyToPaySalary rdfs:subClassOf gufo:ExtrinsicMode .

:DanasRightToSalary a :RightToSalary ;
    gufo:inheresIn :Dana ;
    gufo:externallyDependsOn :GlobexCorp ;
    gufo:isAspectProperPartOf :DanaGlobexEmployment .

:GlobexsDutyToPaySalary a :DutyToPaySalary ;
    gufo:inheresIn :GlobexCorp ;
    gufo:externallyDependsOn :Dana ;
    gufo:isAspectProperPartOf :DanaGlobexEmployment .

The full ontology mirrors this for the other direction of obligation (:DutyToWork / :RightToLabor), giving the employment four extrinsic-mode parts in total -- exactly the "rights towards Amazon, Inc." pattern from the gUFO usage guide, applied to employment instead.

A shortcut property, with its provenance recorded

Applications often still want a plain binary link for querying ("who works where"). gUFO lets you add one without losing the connection to the relator it stands for, by declaring it a gufo:MaterialRelationshipType and pointing gufo:isDerivedFrom at the relator class:

:employedBy a owl:ObjectProperty , gufo:MaterialRelationshipType ;
    rdfs:domain :Employee ;
    rdfs:range :Employer ;
    gufo:isDerivedFrom :Employment .

:Dana :employedBy :GlobexCorp .

gufo:isDerivedFrom is metadata about the property, not a logical link between :Dana :employedBy :GlobexCorp and the specific :DanaGlobexEmployment individual: it tells a reader (or a tool) that this kind of edge always corresponds to some relator of that type, without forcing every use of :employedBy to also assert the relator explicitly. See example 7 for more on this style of typing an object property itself, using OWL 2 punning.

The lightweight alternative: an existential restriction

Not every relator needs distinguishable roles in the data. John and Mary's marriage does not, here, need to tell "husband" from "wife" apart, so :Marriage uses a plain existential restriction on gufo:mediates instead of two dedicated sub-properties:

:Marriage rdfs:subClassOf gufo:Relator ,
    [ a owl:Restriction ; owl:onProperty gufo:mediates ; owl:someValuesFrom :Person ] .

:JohnMaryMarriage a :Marriage ;
    gufo:mediates :John , :Mary ;
    gufo:hasBeginPointInXSDDate "2001-12-12"^^xsd:date .

This is a genuine trade-off, not a shortcut with no cost: querying "who is John's spouse" now means looking at every gufo:mediates value of :JohnMaryMarriage other than John, rather than following a role-specific property directly.