diff --git a/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/IdentifierFactory.java b/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/IdentifierFactory.java
index 02a946154..45e3f84b1 100644
--- a/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/IdentifierFactory.java
+++ b/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/IdentifierFactory.java
@@ -5,39 +5,20 @@ import eu.dnetlib.dhp.schema.oaf.OafEntity;
 import eu.dnetlib.dhp.schema.oaf.StructuredProperty;
 import eu.dnetlib.dhp.utils.DHPUtils;
 import org.apache.commons.lang.StringUtils;
-import org.jetbrains.annotations.NotNull;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 import java.io.Serializable;
-import java.util.HashSet;
 import java.util.Objects;
-import java.util.Set;
 
 /**
  * Factory class for OpenAIRE identifiers in the Graph
  */
 public class IdentifierFactory implements Serializable {
 
-	private static final Logger log = LoggerFactory.getLogger(IdentifierFactory.class);
-
 	public static final String ID_SEPARATOR = "::";
 	public static final String ID_PREFIX_SEPARATOR = "|";
 	public final static String ID_REGEX = "^[0-9][0-9]\\"+ID_PREFIX_SEPARATOR+".{12}"+ID_SEPARATOR+"[a-zA-Z0-9]{32}$";
 	public static final int ID_PREFIX_LEN = 12;
 
-	public static Set<String> acceptedPidTypes = new HashSet<>();
-
-	static {
-		acceptedPidTypes.add("doi");
-		acceptedPidTypes.add("doi");
-		acceptedPidTypes.add("doi");
-		acceptedPidTypes.add("doi");
-		acceptedPidTypes.add("doi");
-		acceptedPidTypes.add("doi");
-
-	}
-
 	public static <T extends OafEntity> String createIdentifier(T entity) {
 
 		if (Objects.isNull(entity.getPid()) || entity.getPid().isEmpty()) {
@@ -48,14 +29,14 @@ public class IdentifierFactory implements Serializable {
 				.getPid()
 				.stream()
 				.filter(s -> Objects.nonNull(s.getQualifier()))
-				.filter(s -> acceptedPidTypes.contains(s.getQualifier().getClassid()))
-				.max(new PidComparator<T>(entity))
+				.filter(s -> PidType.isValid(s.getQualifier().getClassid()))
+				.min(new PidComparator<>(entity))
 				.map(s -> idFromPid(entity, s))
 				.map(IdentifierFactory::verifyIdSyntax)
 				.orElseGet(entity::getId);
 	}
 
-	protected static String verifyIdSyntax(String s) {
+	private static String verifyIdSyntax(String s) {
 		if(StringUtils.isBlank(s) || !s.matches(ID_REGEX)) {
 			throw new RuntimeException(String.format("malformed id: '%s'", s));
 		} else {
@@ -74,7 +55,7 @@ public class IdentifierFactory implements Serializable {
 	}
 
 	private static String normalizePidValue(String value) {
-		//TODO more aggressive cleaning? keep only alphanum and punctation?
+		//TODO more aggressive cleaning? keep only alphanum and punctuation?
 		return value.toLowerCase().replaceAll(" ", "");
 	}
 
diff --git a/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/PidComparator.java b/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/PidComparator.java
index 97bdd9c77..d0a8f87ce 100644
--- a/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/PidComparator.java
+++ b/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/PidComparator.java
@@ -27,8 +27,8 @@ public class PidComparator<T extends OafEntity> implements Comparator<Structured
 		if (right == null)
 			return -1;
 
-		String lClass = left.getQualifier().getClassid();
-		String rClass = right.getQualifier().getClassid();
+		PidType lClass = PidType.valueOf(left.getQualifier().getClassid());
+		PidType rClass = PidType.valueOf(right.getQualifier().getClassid());
 
 		if (lClass.equals(rClass))
 			return 0;
@@ -44,39 +44,69 @@ public class PidComparator<T extends OafEntity> implements Comparator<Structured
 		return lClass.compareTo(rClass);
 	}
 
-	private int compareResultPids(String lClass, String rClass) {
-		if (lClass.equals("doi"))
+	private int compareResultPids(PidType lClass, PidType rClass) {
+		if (lClass.equals(PidType.doi))
 			return -1;
-		if (rClass.equals("doi"))
+		if (rClass.equals(PidType.doi))
 			return 1;
 
-		if (lClass.equals("pmid"))
+		if (lClass.equals(PidType.pmid))
 			return -1;
-		if (rClass.equals("pmid"))
+		if (rClass.equals(PidType.pmid))
 			return 1;
 
-		if (lClass.equals("pmc"))
+		if (lClass.equals(PidType.pmc))
 			return -1;
-		if (rClass.equals("pmc"))
+		if (rClass.equals(PidType.pmc))
+			return 1;
+
+		if (lClass.equals(PidType.handle))
+			return -1;
+		if (rClass.equals(PidType.handle))
+			return 1;
+
+		if (lClass.equals(PidType.arXiv))
+			return -1;
+		if (rClass.equals(PidType.arXiv))
+			return 1;
+
+		if (lClass.equals(PidType.NCID))
+			return -1;
+		if (rClass.equals(PidType.NCID))
+			return 1;
+
+		if (lClass.equals(PidType.GBIF))
+			return -1;
+		if (rClass.equals(PidType.GBIF))
+			return 1;
+
+		if (lClass.equals(PidType.nct))
+			return -1;
+		if (rClass.equals(PidType.nct))
+			return 1;
+
+		if (lClass.equals(PidType.urn))
+			return -1;
+		if (rClass.equals(PidType.urn))
 			return 1;
 
 		return 0;
 	}
 
-	private int compareOrganizationtPids(String lClass, String rClass) {
-		if (lClass.equals("GRID"))
+	private int compareOrganizationtPids(PidType lClass, PidType rClass) {
+		if (lClass.equals(PidType.GRID))
 			return -1;
-		if (rClass.equals("GRID"))
+		if (rClass.equals(PidType.GRID))
 			return 1;
 
-		if (lClass.equals("mag_id"))
+		if (lClass.equals(PidType.mag_id))
 			return -1;
-		if (rClass.equals("mag_id"))
+		if (rClass.equals(PidType.mag_id))
 			return 1;
 
-		if (lClass.equals("urn"))
+		if (lClass.equals(PidType.urn))
 			return -1;
-		if (rClass.equals("urn"))
+		if (rClass.equals(PidType.urn))
 			return 1;
 
 		return 0;
diff --git a/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/PidType.java b/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/PidType.java
new file mode 100644
index 000000000..87af06ec2
--- /dev/null
+++ b/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/PidType.java
@@ -0,0 +1,17 @@
+package eu.dnetlib.dhp.schema.oaf.utils;
+
+import org.apache.commons.lang3.EnumUtils;
+
+public enum PidType {
+
+    // Result
+    doi, pmid, pmc, handle, arXiv, NCID, GBIF, nct, pdb,
+
+    // Organization
+	GRID, mag_id, urn;
+
+    public static boolean isValid(String type) {
+        return EnumUtils.isValidEnum(PidType.class, type);
+    }
+    
+}
diff --git a/dhp-common/src/test/java/eu/dnetlib/dhp/schema/oaf/utils/IdentifierFactoryTest.java b/dhp-common/src/test/java/eu/dnetlib/dhp/schema/oaf/utils/IdentifierFactoryTest.java
new file mode 100644
index 000000000..2d34c58c8
--- /dev/null
+++ b/dhp-common/src/test/java/eu/dnetlib/dhp/schema/oaf/utils/IdentifierFactoryTest.java
@@ -0,0 +1,43 @@
+package eu.dnetlib.dhp.schema.oaf.utils;
+
+import com.fasterxml.jackson.databind.DeserializationFeature;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import eu.dnetlib.dhp.schema.oaf.Publication;
+import eu.dnetlib.dhp.utils.DHPUtils;
+import org.apache.commons.io.IOUtils;
+
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class IdentifierFactoryTest {
+
+    private static ObjectMapper OBJECT_MAPPER = new ObjectMapper().configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
+
+    @Test
+    public void testCreateIdentifierForPublication() throws IOException {
+
+        verifyIdentifier("publication_doi.json", "50|doi_________::" + DHPUtils.md5("10.1016/j.cmet.2011.03.013"));
+        verifyIdentifier("publication_pmc.json", "50|pmc_________::" + DHPUtils.md5("21459329"));
+        verifyIdentifier("publication_urn.json", "50|urn_________::" + DHPUtils.md5("urn:nbn:nl:ui:29-f3ed5f9e-edf6-457e-8848-61b58a4075e2"));
+
+        final String defaultID = "50|DansKnawCris::0829b5191605bdbea36d6502b8c1ce1f";
+        verifyIdentifier("publication_3.json", defaultID);
+        verifyIdentifier("publication_4.json", defaultID);
+        verifyIdentifier("publication_5.json", defaultID);
+    }
+
+    protected void verifyIdentifier(String filename, String expectedID) throws IOException {
+        final String json = IOUtils.toString(getClass().getResourceAsStream(filename));
+        final Publication pub = OBJECT_MAPPER.readValue(json, Publication.class);
+
+        String id = IdentifierFactory.createIdentifier(pub);
+
+        assertNotNull(id);
+        assertEquals(expectedID, id);
+    }
+
+
+}
diff --git a/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_3.json b/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_3.json
new file mode 100644
index 000000000..6d33568f4
--- /dev/null
+++ b/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_3.json
@@ -0,0 +1 @@
+{"id":"50|DansKnawCris::0829b5191605bdbea36d6502b8c1ce1f","pid":[{"qualifier":{"classid":"scp-number"},"value":"79953761260"}]}
\ No newline at end of file
diff --git a/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_4.json b/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_4.json
new file mode 100644
index 000000000..6617fe15f
--- /dev/null
+++ b/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_4.json
@@ -0,0 +1 @@
+{"id":"50|DansKnawCris::0829b5191605bdbea36d6502b8c1ce1f","pid":[]}
\ No newline at end of file
diff --git a/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_5.json b/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_5.json
new file mode 100644
index 000000000..700a10046
--- /dev/null
+++ b/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_5.json
@@ -0,0 +1 @@
+{"id":"50|DansKnawCris::0829b5191605bdbea36d6502b8c1ce1f"}
\ No newline at end of file
diff --git a/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_doi.json b/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_doi.json
new file mode 100644
index 000000000..6865d0ff6
--- /dev/null
+++ b/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_doi.json
@@ -0,0 +1 @@
+{"id":"50|DansKnawCris::0829b5191605bdbea36d6502b8c1ce1f","pid":[{"qualifier":{"classid":"doi"},"value":"10.1016/j.cmet.2011.03.013"},{"qualifier":{"classid":"urn"},"value":"urn:nbn:nl:ui:29-f3ed5f9e-edf6-457e-8848-61b58a4075e2"},{"qualifier":{"classid":"scp-number"},"value":"79953761260"},{"qualifier":{"classid":"pmc"},"value":"21459329"}]}
\ No newline at end of file
diff --git a/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_pmc.json b/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_pmc.json
new file mode 100644
index 000000000..3e4ba2246
--- /dev/null
+++ b/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_pmc.json
@@ -0,0 +1 @@
+{"id":"50|DansKnawCris::0829b5191605bdbea36d6502b8c1ce1f","pid":[{"qualifier":{"classid":"urn"},"value":"urn:nbn:nl:ui:29-f3ed5f9e-edf6-457e-8848-61b58a4075e2"},{"qualifier":{"classid":"scp-number"},"value":"79953761260"},{"qualifier":{"classid":"pmc"},"value":"21459329"}]}
\ No newline at end of file
diff --git a/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_urn.json b/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_urn.json
new file mode 100644
index 000000000..83e14e48d
--- /dev/null
+++ b/dhp-common/src/test/resources/eu/dnetlib/dhp/schema/oaf/utils/publication_urn.json
@@ -0,0 +1 @@
+{"id":"50|DansKnawCris::0829b5191605bdbea36d6502b8c1ce1f","pid":[{"qualifier":{"classid":"urn"},"value":"urn:nbn:nl:ui:29-f3ed5f9e-edf6-457e-8848-61b58a4075e2"},{"qualifier":{"classid":"scp-number"},"value":"79953761260"},{"qualifier":{"classid":"pmcid"},"value":"21459329"}]}
\ No newline at end of file