diff --git a/src/main/java/eu/dnetlib/dhp/schema/common/ModelSupport.java b/src/main/java/eu/dnetlib/dhp/schema/common/ModelSupport.java
index 8639d55..db203c1 100644
--- a/src/main/java/eu/dnetlib/dhp/schema/common/ModelSupport.java
+++ b/src/main/java/eu/dnetlib/dhp/schema/common/ModelSupport.java
@@ -158,6 +158,21 @@ public class ModelSupport {
 		}
 	}
 
+	/**
+	 * Helper method: lookup relation inverse, given the direct relation encoding (case insensitive)
+	 * @param encoding
+	 * @return the relation inverse descriptor, throws @IllegalArgumentException when not found.
+	 */
+	private RelationInverse findInverse(String encoding) {
+		return ModelSupport.relationInverseMap
+				.entrySet()
+				.stream()
+				.filter(r -> encoding.equalsIgnoreCase(r.getKey()))
+				.findFirst()
+				.map(r -> r.getValue())
+				.orElseThrow(() -> new IllegalArgumentException("invalid relationship: " + encoding));
+	}
+
 	/**
 	 * Helper method: fina a relation filtering by a relation name
  	 * @param relationName