diff --git a/src/main/java/eu/dnetlib/dhp/schema/oaf/Relation.java b/src/main/java/eu/dnetlib/dhp/schema/oaf/Relation.java
index 17f1378..11812da 100644
--- a/src/main/java/eu/dnetlib/dhp/schema/oaf/Relation.java
+++ b/src/main/java/eu/dnetlib/dhp/schema/oaf/Relation.java
@@ -9,18 +9,21 @@ import java.util.Objects;
 
 /**
  * Relation models any edge between two nodes in the OpenAIRE graph. It has a source id and a target id pointing to
- * graph node identifiers and it is further characterised by the semantic of the link through the fields relType,
+ * graph node identifiers, and it is further characterised by the semantic of the link through the fields relType,
  * subRelType and relClass. Provenance information is modeled according to the dataInfo element and collectedFrom, while
  * individual relationship types can provide extra information via the properties field.
  */
 public class Relation extends Oaf implements Serializable {
 
+
     public enum RELTYPE {
         resultResult,
         resultProject,
         resultOrganization,
         projectOrganization,
         datasourceOrganization
+
+        //TODO organizationOrganization ????
     }
 
     public enum SUBRELTYPE {
@@ -36,8 +39,7 @@ public class Relation extends Oaf implements Serializable {
         similarity,
         supplement,
         version;
-
-        public boolean exists(String subreltype) {
+        public static boolean exists(String subreltype) {
             try {
                 SUBRELTYPE.valueOf(subreltype);
                 return true;
@@ -83,6 +85,7 @@ public class Relation extends Oaf implements Serializable {
         IsVariantFormOf,
         isProducedBy,
         IsMetadataFor,
+        HasAssociationWith,
         Cites,
         IsRequiredBy,
         IsOriginalFormOf,
@@ -95,6 +98,7 @@ public class Relation extends Oaf implements Serializable {
         IsDerivedFrom,
         Obsoletes,
         Reviews,
+        isSimilarTo,
         produces;
 
         public static boolean exists(String relclass) {
@@ -105,6 +109,75 @@ public class Relation extends Oaf implements Serializable {
                 return false;
             }
         }
+        @Transient
+        public SUBRELTYPE getSubRel() {
+            switch (this) {
+                case isParticipant:
+                case hasParticipant:
+                    return  SUBRELTYPE.participation;
+                case isAuthorInstitutionOf:
+                case hasAuthorInstitution:
+                    return SUBRELTYPE.affiliation;
+                case isMergedIn:
+                case merges:
+                case isSimilarTo:
+                    return SUBRELTYPE.dedup;
+                case isProducedBy:
+                case produces:
+                    return SUBRELTYPE.outcome;
+                case isProvidedBy:
+                case provides:
+                    return SUBRELTYPE.provision;
+                case IsAmongTopNSimilarDocuments:
+                case HasAmongTopNSimilarDocuments:
+                    return SUBRELTYPE.similarity;
+                case IsSupplementedBy:
+                case IsSupplementTo:
+                    return SUBRELTYPE.supplement;
+                case IsPartOf:
+                case HasPart:
+                    return SUBRELTYPE.part;
+                case IsCitedBy:
+                case Cites:
+                    return SUBRELTYPE.citation;
+                case IsIdenticalTo:
+                case IsReferencedBy:
+                case References:
+                case IsContinuedBy:
+                case Continues:
+                case IsDocumentedBy:
+                case Documents:
+                case IsDerivedFrom:
+                case IsSourceOf:
+                case IsRelatedTo:
+                case IsCompiledBy:
+                case Compiles:
+                case IsDescribedBy:
+                case Describes:
+                case IsMetadataFor:
+                case IsMetadataOf:
+                case HasAssociationWith:
+                case IsRequiredBy:
+                case Requires:
+                case IsChildOf:
+                case IsParentOf:
+                    return SUBRELTYPE.relationship;
+                case IsPreviousVersionOf:
+                case IsNewVersionOf:
+                case IsVariantFormOf:
+                case IsOriginalFormOf:
+                case IsObsoletedBy:
+                case Obsoletes:
+                case IsVersionOf:
+                case HasVersion:
+                    return SUBRELTYPE.version;
+                case IsReviewedBy:
+                case Reviews:
+                    return SUBRELTYPE.review;
+            }
+            // makes the compiler happy
+            throw new IllegalArgumentException("missing SubRel mapping for" + this);
+        }
 
         @Transient
         public RELCLASS getInverse() {
@@ -341,6 +414,20 @@ public class Relation extends Oaf implements Serializable {
                 && target.equals(relation.target);
     }
 
+    public Relation inverse() {
+        final Relation inverse = new Relation();
+        inverse.setSource(this.target);
+        inverse.setTarget(this.source);
+        inverse.setRelClass(this.relClass.getInverse());
+        inverse.setRelType(this.relType);
+        inverse.setSubRelType(this.subRelType);
+        inverse.setProperties(this.properties);
+        inverse.setValidated(validated);
+        inverse.setProvenance(provenance);
+        inverse.setValidationDate(validationDate);
+        return inverse;
+    }
+
     @Override
     public int hashCode() {
         return Objects.hash(relType, subRelType, relClass, source, target, provenance);
diff --git a/src/test/java/eu/dnetlib/dhp/schema/oaf/RelationTest.java b/src/test/java/eu/dnetlib/dhp/schema/oaf/RelationTest.java
new file mode 100644
index 0000000..6b14242
--- /dev/null
+++ b/src/test/java/eu/dnetlib/dhp/schema/oaf/RelationTest.java
@@ -0,0 +1,26 @@
+package eu.dnetlib.dhp.schema.oaf;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+public class RelationTest {
+
+    @Test
+    public void checkExistRelType() {
+        assertTrue(Relation.SUBRELTYPE.exists(Relation.SUBRELTYPE.dedup.toString()));
+        assertFalse(Relation.SUBRELTYPE.exists("foo"));
+
+    }
+    @Test
+    public void checSubRelType() {
+        Relation.RELCLASS rc = Relation.RELCLASS.merges;
+        assertEquals(Relation.SUBRELTYPE.dedup, rc.getSubRel());
+
+        for (Relation.RELCLASS value : Relation.RELCLASS.values()) {
+            System.out.printf("%s  => %s\n", value, value.getSubRel());
+
+        }
+    }
+
+}