OWL

OWL, aka One World Language, is a xml format created in 2004.

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20Years Old

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The Web Ontology Language (OWL) is a family of knowledge representation languages for authoring ontologies. Ontologies are a formal way to describe taxonomies and classification networks, essentially defining the structure of knowledge for various domains: the nouns representing classes of objects and the verbs representing relations between the objects. Ontologies resemble class hierarchies in object-oriented programming but there are several critical differences. Read more on Wikipedia...

OWL Wikipedia page
OWL docs
There are at least 199 OWL repos on GitHub
OWL first developed in World Wide Web Consortium
file extensions for OWL include owl
The Google BigQuery Public Dataset GitHub snapshot shows 524 users using OWL in 642 repos on GitHub
OWL on HOPL
GitHub supports syntax highlighting for OWL
See also: (8 related languages)RDF, XML, HTML, AXIOM, Turtle, SQL, Prolog, UML

Example from Linguist:

<?xml version="1.0"?>


<!DOCTYPE rdf:RDF [
    <!ENTITY owl "http://www.w3.org/2002/07/owl#" >
    <!ENTITY xsd "http://www.w3.org/2001/XMLSchema#" >
    <!ENTITY rdfs "http://www.w3.org/2000/01/rdf-schema#" >
    <!ENTITY rdf "http://www.w3.org/1999/02/22-rdf-syntax-ns#" >
]>


<rdf:RDF xmlns="http://www.co-ode.org/ontologies/pizza/pizza.owl#"
     xml:base="http://www.co-ode.org/ontologies/pizza/pizza.owl"
     xmlns:xsd="http://www.w3.org/2001/XMLSchema#"
     xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
     xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
     xmlns:owl="http://www.w3.org/2002/07/owl#">
    <owl:Ontology rdf:about="">
        <owl:versionInfo xml:lang="en"
            >v.1.4. Added Food class (used in domain/range of hasIngredient), Added several hasCountryOfOrigin restrictions on pizzas, Made hasTopping invers functional</owl:versionInfo>
        <owl:versionInfo rdf:datatype="&xsd;string">version 1.5</owl:versionInfo>
        <owl:versionInfo xml:lang="en"
            >v.1.5. Removed protege.owl import and references. Made ontology URI date-independent</owl:versionInfo>
        <rdfs:comment xml:lang="en"
            >An example ontology that contains all constructs required for the various versions of the Pizza Tutorial run by Manchester University (see http://www.co-ode.org/resources/tutorials/)</rdfs:comment>
    </owl:Ontology>
    


    <!-- 
    ///////////////////////////////////////////////////////////////////////////
    //
    //   OWL Classes
    //
    ///////////////////////////////////////////////////////////////////////////
     -->

    


    <!-- Class: http://www.co-ode.org/ontologies/pizza/pizza.owl#American -->

    <owl:Class rdf:about="#American">
        <rdfs:label xml:lang="pt">Americana</rdfs:label>
        <rdfs:subClassOf>
            <owl:Restriction>
                <owl:onProperty rdf:resource="#hasTopping"/>
                <owl:someValuesFrom rdf:resource="#TomatoTopping"/>
            </owl:Re

Example from Wikipedia:

<http://example.org/tea.owl> rdf:type owl:Ontology .
 :Tea  rdf:type            owl:Class .

OWL - Xml format

Language features