diff --git a/RDFSharp/Model/RDFFacet.cs b/RDFSharp/Model/RDFFacet.cs
index ac849e7f..d4588ba8 100644
--- a/RDFSharp/Model/RDFFacet.cs
+++ b/RDFSharp/Model/RDFFacet.cs
@@ -32,7 +32,7 @@ public abstract class RDFFacet
 		/// <summary>
 		/// Builds a facet by initializing its blank URI
 		/// </summary>
-		public RDFFacet() 
+		internal RDFFacet() 
 			=> URI = new RDFResource();
 		#endregion
 
@@ -40,14 +40,12 @@ public RDFFacet()
 		/// <summary>
 		/// Validates the given literal against the facet
 		/// </summary>
-		public virtual bool Validate(string literalValue) 
-			=> false;
+		public abstract bool Validate(string literalValue);
 
 		/// <summary>
 		/// Gives a graph representation of the facet
 		/// </summary>
-		public virtual RDFGraph ToRDFGraph() 
-			=> null;
+		public abstract RDFGraph ToRDFGraph();
 		#endregion
 	}
 }
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