OWL => C# T4 template

sample.csproj

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="4.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <ItemGroup>
    <!-- This way the FOAF.tt will generate a Foaf class with fields for prefix, base URI and all vocabulary members -->
    <Compile Include="Ontologies\FOAF.cs">
      <AutoGen>True</AutoGen>
      <DesignTime>True</DesignTime>
      <DependentUpon>FOAF.tt</DependentUpon>
    </Compile>
  </ItemGroup>
</Project>

Sample.tt

<# // Create exact file grouped with your OWL/XML file. See example below of csproj structure #>

<#@ assembly name="System.Core" #>
<#@ assembly name="System.Xml" #>
<#@ import namespace="System.Xml" #>
<#@ include file="Vocabulary.tt" #><#
    CreateVocabulary();
#>

vocabulary.tt

<#@ template debug="false" hostspecific="true" language="C#" #>
<#@ assembly name="System.Core" #>
<#@ assembly name="System.Xml" #>
<#@ assembly name="EnvDTE" #>
<#@ import namespace="System.Collections.Generic" #>
<#@ import namespace="System.Linq" #>
<#@ import namespace="System.Text.RegularExpressions" #>
<#@ import namespace="System.Xml" #>
<#@ import namespace="Microsoft.VisualStudio.TextTemplating" #>
<#@ output extension=".cs" #><#+
    public void CreateVocabulary()
    {
        string prefix;
        string ns;
        string uri;
        string className;
        XmlNamespaceManager namespaceManager;
        bool isRDFMode;
        XmlDocument ontology=Initialize(out prefix,out uri,out ns,out className,out namespaceManager,out isRDFMode);
#>
// <auto-generated />
using System;

namespace <#=ns #>
{
    /// <summary><#=GetTitle(ontology.DocumentElement,namespaceManager,isRDFMode) #> (<#=uri #>).</summary>
    public static partial class <#=className #>
    {
        /// <summary>
        /// <#=className.ToLower() #>
        /// </summary>
        public const string Prefix="<#=className.ToLower() #>";

        /// <summary>
        /// <#=uri #>
        /// </summary>
        public const string BaseUri="<#=uri #>";
<#+
        IEnumerable<XmlNode> classes=GetNodes(ontology.DocumentElement,namespaceManager,"rdfs:Class",isRDFMode).Union(
            GetNodes(ontology.DocumentElement,namespaceManager,"owl:Class",isRDFMode));
        foreach (XmlNode classNode in classes)
        {#>
        
        /// <summary>
        /// <#=GetDescription(classNode, namespaceManager) #>
        /// </summary>
        public const string <#=GetTermName(classNode,namespaceManager) #> = BaseUri + "<#=GetTermName(classNode,namespaceManager) #>";
<#+     }

        IEnumerable<XmlNode> properties=GetNodes(ontology.DocumentElement,namespaceManager,"rdf:Property",isRDFMode).Union(
            GetNodes(ontology.DocumentElement,namespaceManager,"owl:DatatypeProperty",isRDFMode)).Union(
            GetNodes(ontology.DocumentElement,namespaceManager,"owl:ObjectProperty",isRDFMode)).Union(
            GetNodes(ontology.DocumentElement,namespaceManager,"owl:AnnotationProperty",isRDFMode)).Union(
            GetNodes(ontology.DocumentElement,namespaceManager,"hydra:Link",isRDFMode));
        foreach (XmlNode propertyNode in properties)
        {#>
        
        /// <summary>
        /// <#=GetDescription(propertyNode, namespaceManager) #>
        /// </summary>
        public const string <#=GetTermName(propertyNode,namespaceManager) #> = BaseUri + "<#=GetTermName(propertyNode,namespaceManager).Replace("@",System.String.Empty) #>";
<#+		}

        string rdf=namespaceManager.LookupNamespace("rdf");
        foreach (XmlNode classNode in classes)
        {
            string typeName=StandardizeTerm((classNode.Attributes["about",rdf]!=null?classNode.Attributes["about",rdf]:classNode.Attributes["ID",rdf]).Value,namespaceManager);
            if ((typeName!="rdfs:Class")&&(typeName!="rdf:Property")&&(typeName!="owl:Class")&&((!typeName.StartsWith("owl:"))&&(!typeName.EndsWith("Property"))))
            {
                IEnumerable<XmlNode> namedInstances=GetNodes(ontology.DocumentElement,namespaceManager,typeName,isRDFMode);
                foreach (XmlNode namedInstanceNode in namedInstances)
                {#>
        /// <summary>
        /// <#=GetDescription(namedInstanceNode, namespaceManager) #>
        /// </summary>
        public const string <#=GetTermName(namedInstanceNode,namespaceManager) #> = BaseUri + "<#=GetTermName(namedInstanceNode,namespaceManager).Replace("@",System.String.Empty) #>";
<#+				}
            }
        }
#>
    }
}<#+
    }

    private XmlDocument Initialize(out string prefix,out string uri,out string ns,out string className,out XmlNamespaceManager namespaceManager,out bool isRDFMode)
    {
        prefix=System.String.Empty;
        uri=System.String.Empty;
        ns=System.String.Empty;
        className=System.String.Empty;
        namespaceManager=null;
        isRDFMode=false;
        string fileName;
        string rdfFile=System.IO.Path.ChangeExtension(this.Host.TemplateFile, "rdf");
        string owlFile=System.IO.Path.ChangeExtension(this.Host.TemplateFile, "owl");

        if(System.IO.File.Exists(rdfFile))
        {
            fileName = rdfFile;
        }
        else if(System.IO.File.Exists(owlFile)) 
        {
            fileName = owlFile;
        }
        else 
        {
            throw new Exception(string.Format("Cannot find ontology file. Tried {0} and {1}", owlFile, rdfFile));
        }
        
        XmlDocument result=new XmlDocument();
        result.Load(fileName);
        prefix=System.IO.Path.GetFileNameWithoutExtension(this.Host.TemplateFile);
        className=(prefix.Count(item => Char.IsUpper(item))==prefix.Length?prefix.Substring(0,1).ToUpper()+prefix.Substring(1).ToLower():prefix);
        prefix=prefix.ToLower();
        IDictionary<string,string> namespaces=result.DocumentElement.CreateNavigator().GetNamespacesInScope(XmlNamespaceScope.All);
        uri=namespaces[prefix];
        var nsHint = System.Runtime.Remoting.Messaging.CallContext.LogicalGetData("NamespaceHint");
        ns = (nsHint ?? "Vocab").ToString();
        isRDFMode=(System.IO.Path.GetExtension(fileName).Substring(1).ToLower()=="rdf");
        namespaceManager=new XmlNamespaceManager(result.NameTable);
        namespaceManager.AddNamespace("rdf","http://www.w3.org/1999/02/22-rdf-syntax-ns#");
        namespaceManager.AddNamespace("rdfs","http://www.w3.org/2000/01/rdf-schema#");
        namespaceManager.AddNamespace("owl","http://www.w3.org/2002/07/owl#");
        namespaceManager.AddNamespace("dc","http://purl.org/dc/elements/1.1/");
        namespaceManager.AddNamespace("dcterms","http://purl.org/dc/terms/");
        namespaceManager.AddNamespace("skos","http://www.w3.org/2004/02/skos/core#");
        namespaceManager.AddNamespace("hydra","http://www.w3.org/ns/hydra/core#");
        foreach (KeyValuePair<string,string> @namespace in namespaces)
        {
            if (System.String.IsNullOrEmpty(namespaceManager.LookupPrefix(@namespace.Value)))
            {
                namespaceManager.AddNamespace(@namespace.Key,@namespace.Value);
            }
        }

        namespaceManager.AddNamespace("base",namespaceManager.LookupNamespace(prefix));
        return result;
    }

    private string GetTermName(XmlNode node,XmlNamespaceManager namespaceManager)
    {
        string result=null;
        string rdf=namespaceManager.LookupNamespace("rdf");
        XmlAttribute attribute=node.Attributes["about",rdf];
        if (attribute==null)
        {
            result=namespaceManager.LookupNamespace("base")+node.Attributes["ID",rdf].Value;
        }
        else
        {
            result=attribute.Value;
        }

        if (result.IndexOf('#')!=-1)
        {
            result=result.Substring(result.IndexOf('#')+1);
        }
        else if(result.Contains(":"))
        {
            result=new Uri(result).Segments.Last();
        }

        string[] keywords=new string[] { "object","class","readonly","abstract","private","default","as","using","event" };
        if (keywords.Contains(result))
        {
            result="@"+result;
        }

        return result;
    }

    private string GetDescription(XmlNode node,XmlNamespaceManager namespaceManager)
    {
        string result = null;
        XmlNode title=node.SelectSingleNode("*[(self::rdfs:comment) or (self::skos:definition)]",namespaceManager);
        if (title!=null)
        {
            result=title.InnerText;
        }
        else
        {
            XmlAttribute attribute=node.Attributes["comment",namespaceManager.LookupNamespace("rdfs")]??(node.Attributes["definition",namespaceManager.LookupNamespace("skos")]);
            if (attribute!=null)
            {
                result=attribute.Value;
            }
        }

        result = result ?? GetTermName(node, namespaceManager);
        if(result != null)
        {
            result = result.Replace(Environment.NewLine, " ").Replace("\n", " ");
        }

        return result;
    }

    private string GetTitle(XmlNode documentElement,XmlNamespaceManager namespaceManager,bool isRDFMode)
    {
        XmlNode ontology=documentElement.SelectSingleNode((isRDFMode?"rdf:Description[rdf:type[@rdf:resource=\"http://www.w3.org/2002/07/owl#Ontology\"]]":"owl:Ontology"),namespaceManager);
        string result=GetTermName(ontology,namespaceManager);
        XmlNode title=ontology.SelectSingleNode("*[(self::rdfs:label) or (self::dc:title) or (self::dcterms:title)]",namespaceManager);
        if (title!=null)
        {
            result=title.InnerText;
        }
        else
        {
            XmlAttribute attribute=ontology.Attributes["label",namespaceManager.LookupNamespace("rdfs")]??(ontology.Attributes["title",namespaceManager.LookupNamespace("dc")]??documentElement.Attributes["title",namespaceManager.LookupNamespace("dcterms")]);
            if (attribute!=null)
            {
                result=attribute.Value;
            }
        }

        return result;
    }

    private IEnumerable<XmlNode> GetNodes(XmlNode node,XmlNamespaceManager namespaceManager,string name,bool isRDFMode)
    {
        name=StandardizeTerm(name,namespaceManager);
        XmlNodeList result=null;
        if (isRDFMode)
        {
            result=node.SelectNodes("rdf:Description[@rdf:about and rdf:type[@rdf:resource=\""+namespaceManager.LookupNamespace(name.Split(':')[0])+name.Split(':')[1]+"\"]]",namespaceManager);
        }
        else
        {
            result=node.SelectNodes(name,namespaceManager);
        }

        string rdf = namespaceManager.LookupNamespace("rdf");
        string ns = namespaceManager.LookupNamespace("base");
        return from item in result.Cast<XmlNode>()
               where HasAbout(item, rdf, ns) || HasID(item, rdf)
               select item;
    }

    private static bool HasAbout(XmlNode item, string rdf, string ns)
    {
        var about = item.Attributes["about", rdf];
        var isRelativeUri = about.Value.Contains(":") == false;
        return about.Value.StartsWith(ns) || isRelativeUri;
    }

    private static bool HasID(XmlNode item, string rdf)
    {
        return item.Attributes["ID", rdf] != null;
    }

    private string StandardizeTerm(string term,XmlNamespaceManager namespaceManager)
    {
        if ((!Regex.IsMatch(term,"[^:]+://"))&&(!Regex.IsMatch(term,"[^:]+:[a-zA-Z]")))
        {
            term=namespaceManager.LookupNamespace("base")+term;
        }

        namespaceManager.Cast<string>().Where(item => item.Length>0).Select(item => term=term.Replace(namespaceManager.LookupNamespace(item),item+":")).ToList();
        return term;
    }
#>

I never really attempted to make the script reusable. It is part of the build and the Rdf.Vocabularies package is only a way to distribute what was generated

TL;DR; of what's happening:

1. run scripty during build: Rdf.Vocabularies/Rdf.Vocabularies.csproj#L26
2. Rdf.Vocabularies/Vocabs.csx is a meta script which simply run transformation for every source file
   • can be any format parsed by dotNetRDF
   • note there are some parameters because vocabulary files are not made equals
3. Rdf.Vocabularies/MakeVocab.csx script iterated the vocabulary terms and generates a C# class

You should have no issues just reusing those scripts in your project. Or you could submit a PR to the package if yours is a shared vocabulary.

Thanks so much, Tomasz!