diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Dataset.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Dataset.java
index 25fd7e5d5..2b5562b4c 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Dataset.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Dataset.java
@@ -3,7 +3,7 @@ package eu.dnetlib.dhp.schema.oaf;
 import java.io.Serializable;
 import java.util.List;
 
-public class Dataset extends Result implements Serializable {
+public class Dataset extends Result<Dataset> implements Serializable {
 
     private Field<String> storagedate;
 
@@ -81,4 +81,9 @@ public class Dataset extends Result implements Serializable {
         this.geolocation = geolocation;
         return this;
     }
+
+    @Override
+    protected Dataset self() {
+        return this;
+    }
 }
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Datasource.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Datasource.java
index 33e994d4a..ca261bec7 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Datasource.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Datasource.java
@@ -3,7 +3,7 @@ package eu.dnetlib.dhp.schema.oaf;
 import java.io.Serializable;
 import java.util.List;
 
-public class Datasource extends OafEntity implements Serializable {
+public class Datasource extends OafEntity<Datasource> implements Serializable {
 
     private Qualifier datasourcetype;
 
@@ -396,4 +396,9 @@ public class Datasource extends OafEntity implements Serializable {
         this.journal = journal;
         return this;
     }
+
+    @Override
+    protected Datasource self() {
+        return this;
+    }
 }
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Oaf.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Oaf.java
index 2924deaba..5d198c4e6 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Oaf.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Oaf.java
@@ -2,27 +2,29 @@ package eu.dnetlib.dhp.schema.oaf;
 
 import java.io.Serializable;
 
-public abstract class Oaf implements Serializable {
+public abstract class Oaf<T extends Oaf<T>> implements Serializable {
     
     private DataInfo dataInfo;
 
     private Long lastupdatetimestamp;
 
+    protected abstract T self();
+
     public DataInfo getDataInfo() {
         return dataInfo;
     }
 
-    public Oaf setDataInfo(DataInfo dataInfo) {
+    public T setDataInfo(DataInfo dataInfo) {
         this.dataInfo = dataInfo;
-        return this;
+        return self();
     }
 
     public Long getLastupdatetimestamp() {
         return lastupdatetimestamp;
     }
 
-    public Oaf setLastupdatetimestamp(Long lastupdatetimestamp) {
+    public T setLastupdatetimestamp(Long lastupdatetimestamp) {
         this.lastupdatetimestamp = lastupdatetimestamp;
-        return this;
+        return self();
     }
 }
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/OafEntity.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/OafEntity.java
index f00d38583..5e5fdd70b 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/OafEntity.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/OafEntity.java
@@ -3,7 +3,7 @@ package eu.dnetlib.dhp.schema.oaf;
 import java.io.Serializable;
 import java.util.List;
 
-public abstract class OafEntity extends Oaf implements Serializable {
+public abstract class OafEntity<T extends OafEntity<T>> extends Oaf<T> implements Serializable {
 
     private String id;
 
@@ -21,76 +21,75 @@ public abstract class OafEntity extends Oaf implements Serializable {
 
     private OAIProvenance oaiprovenance;
 
-
     public String getId() {
         return id;
     }
 
-    public OafEntity setId(String id) {
+    public T setId(String id) {
         this.id = id;
-        return this;
+        return self();
     }
 
     public List<String> getOriginalId() {
         return originalId;
     }
 
-    public OafEntity setOriginalId(List<String> originalId) {
+    public T setOriginalId(List<String> originalId) {
         this.originalId = originalId;
-        return this;
+        return self();
     }
 
     public List<KeyValue> getCollectedfrom() {
         return collectedfrom;
     }
 
-    public OafEntity setCollectedfrom(List<KeyValue> collectedfrom) {
+    public T setCollectedfrom(List<KeyValue> collectedfrom) {
         this.collectedfrom = collectedfrom;
-        return this;
+        return self();
     }
 
     public List<StructuredProperty> getPid() {
         return pid;
     }
 
-    public OafEntity setPid(List<StructuredProperty> pid) {
+    public T setPid(List<StructuredProperty> pid) {
         this.pid = pid;
-        return this;
+        return self();
     }
 
     public String getDateofcollection() {
         return dateofcollection;
     }
 
-    public OafEntity setDateofcollection(String dateofcollection) {
+    public T setDateofcollection(String dateofcollection) {
         this.dateofcollection = dateofcollection;
-        return this;
+        return self();
     }
 
     public String getDateoftransformation() {
         return dateoftransformation;
     }
 
-    public OafEntity setDateoftransformation(String dateoftransformation) {
+    public T setDateoftransformation(String dateoftransformation) {
         this.dateoftransformation = dateoftransformation;
-        return this;
+        return self();
     }
 
     public List<ExtraInfo> getExtraInfo() {
         return extraInfo;
     }
 
-    public OafEntity setExtraInfo(List<ExtraInfo> extraInfo) {
+    public T setExtraInfo(List<ExtraInfo> extraInfo) {
         this.extraInfo = extraInfo;
-        return this;
+        return self();
     }
 
     public OAIProvenance getOaiprovenance() {
         return oaiprovenance;
     }
 
-    public OafEntity setOaiprovenance(OAIProvenance oaiprovenance) {
+    public T setOaiprovenance(OAIProvenance oaiprovenance) {
         this.oaiprovenance = oaiprovenance;
-        return this;
+        return self();
     }
 }
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Organization.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Organization.java
index 260fc22b6..c03a78419 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Organization.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Organization.java
@@ -3,7 +3,7 @@ package eu.dnetlib.dhp.schema.oaf;
 import java.io.Serializable;
 import java.util.List;
 
-public class Organization extends OafEntity implements Serializable {
+public class Organization extends OafEntity<Organization> implements Serializable {
 
     private Field<String> legalshortname;
 
@@ -180,4 +180,9 @@ public class Organization extends OafEntity implements Serializable {
         this.country = country;
         return this;
     }
+
+    @Override
+    protected Organization self() {
+        return this;
+    }
 }
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/OtherResearchProducts.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/OtherResearchProducts.java
index 3ca231587..3fdf1ae32 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/OtherResearchProducts.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/OtherResearchProducts.java
@@ -3,7 +3,7 @@ package eu.dnetlib.dhp.schema.oaf;
 import java.io.Serializable;
 import java.util.List;
 
-public class OtherResearchProducts extends Result implements Serializable {
+public class OtherResearchProducts extends Result<OtherResearchProducts> implements Serializable {
 
     private List<Field<String>> contactperson;
 
@@ -37,4 +37,9 @@ public class OtherResearchProducts extends Result implements Serializable {
         this.tool = tool;
         return this;
     }
+
+    @Override
+    protected OtherResearchProducts self() {
+        return this;
+    }
 }
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Project.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Project.java
index 5efe1526f..13e0b4431 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Project.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Project.java
@@ -3,7 +3,7 @@ package eu.dnetlib.dhp.schema.oaf;
 import java.io.Serializable;
 import java.util.List;
 
-public class Project extends OafEntity implements Serializable {
+public class Project extends OafEntity<Project> implements Serializable {
 
     private Field<String> websiteurl;
 
@@ -290,4 +290,9 @@ public class Project extends OafEntity implements Serializable {
         this.fundedamount = fundedamount;
         return this;
     }
+
+    @Override
+    protected Project self() {
+        return this;
+    }
 }
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Publication.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Publication.java
index bf4eab93c..29e1cb02f 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Publication.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Publication.java
@@ -2,7 +2,7 @@ package eu.dnetlib.dhp.schema.oaf;
 
 import java.io.Serializable;
 
-public class Publication extends Result implements Serializable {
+public class Publication extends Result<Publication> implements Serializable {
 
     // publication specific
     private Journal journal;
@@ -15,4 +15,9 @@ public class Publication extends Result implements Serializable {
         this.journal = journal;
         return this;
     }
+
+    @Override
+    protected Publication self() {
+        return self();
+    }
 }
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Relation.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Relation.java
index db8807e21..da1b4b439 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Relation.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Relation.java
@@ -2,7 +2,7 @@ package eu.dnetlib.dhp.schema.oaf;
 
 import java.util.List;
 
-public class Relation extends Oaf {
+public class Relation extends Oaf<Relation> {
 
     private String relType;
 
@@ -22,7 +22,7 @@ public class Relation extends Oaf {
 
     public Relation setRelType(String relType) {
         this.relType = relType;
-        return this;
+        return self();
     }
 
     public String getSubRelType() {
@@ -31,7 +31,7 @@ public class Relation extends Oaf {
 
     public Relation setSubRelType(String subRelType) {
         this.subRelType = subRelType;
-        return this;
+        return self();
     }
 
     public String getRelClass() {
@@ -40,7 +40,7 @@ public class Relation extends Oaf {
 
     public Relation setRelClass(String relClass) {
         this.relClass = relClass;
-        return this;
+        return self();
     }
 
     public String getSource() {
@@ -49,7 +49,7 @@ public class Relation extends Oaf {
 
     public Relation setSource(String source) {
         this.source = source;
-        return this;
+        return self();
     }
 
     public String getTarget() {
@@ -58,7 +58,7 @@ public class Relation extends Oaf {
 
     public Relation setTarget(String target) {
         this.target = target;
-        return this;
+        return self();
     }
 
     public List<KeyValue> getCollectedFrom() {
@@ -67,6 +67,11 @@ public class Relation extends Oaf {
 
     public Relation setCollectedFrom(List<KeyValue> collectedFrom) {
         this.collectedFrom = collectedFrom;
+        return self();
+    }
+
+    @Override
+    protected Relation self() {
         return this;
     }
 }
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Result.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Result.java
index b0630825a..b496e9683 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Result.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Result.java
@@ -3,7 +3,7 @@ package eu.dnetlib.dhp.schema.oaf;
 import java.io.Serializable;
 import java.util.List;
 
-public abstract class Result extends OafEntity implements Serializable {
+public abstract class Result<T extends Result<T>> extends OafEntity<T> implements Serializable {
 
     private List<Author> author;
 
@@ -53,188 +53,188 @@ public abstract class Result extends OafEntity implements Serializable {
         return author;
     }
 
-    public Result setAuthor(List<Author> author) {
+    public T setAuthor(List<Author> author) {
         this.author = author;
-        return this;
+        return self();
     }
 
     public Qualifier getResulttype() {
         return resulttype;
     }
 
-    public Result setResulttype(Qualifier resulttype) {
+    public T setResulttype(Qualifier resulttype) {
         this.resulttype = resulttype;
-        return this;
+        return self();
     }
 
     public Qualifier getLanguage() {
         return language;
     }
 
-    public Result setLanguage(Qualifier language) {
+    public T setLanguage(Qualifier language) {
         this.language = language;
-        return this;
+        return self();
     }
 
     public List<Qualifier> getCountry() {
         return country;
     }
 
-    public Result setCountry(List<Qualifier> country) {
+    public T setCountry(List<Qualifier> country) {
         this.country = country;
-        return this;
+        return self();
     }
 
     public List<StructuredProperty> getSubject() {
         return subject;
     }
 
-    public Result setSubject(List<StructuredProperty> subject) {
+    public T setSubject(List<StructuredProperty> subject) {
         this.subject = subject;
-        return this;
+        return self();
     }
 
     public List<StructuredProperty> getTitle() {
         return title;
     }
 
-    public Result setTitle(List<StructuredProperty> title) {
+    public T setTitle(List<StructuredProperty> title) {
         this.title = title;
-        return this;
+        return self();
     }
 
     public List<StructuredProperty> getRelevantdate() {
         return relevantdate;
     }
 
-    public Result setRelevantdate(List<StructuredProperty> relevantdate) {
+    public T setRelevantdate(List<StructuredProperty> relevantdate) {
         this.relevantdate = relevantdate;
-        return this;
+        return self();
     }
 
     public List<Field<String>> getDescription() {
         return description;
     }
 
-    public Result setDescription(List<Field<String>> description) {
+    public T setDescription(List<Field<String>> description) {
         this.description = description;
-        return this;
+        return self();
     }
 
     public Field<String> getDateofacceptance() {
         return dateofacceptance;
     }
 
-    public Result setDateofacceptance(Field<String> dateofacceptance) {
+    public T setDateofacceptance(Field<String> dateofacceptance) {
         this.dateofacceptance = dateofacceptance;
-        return this;
+        return self();
     }
 
     public Field<String> getPublisher() {
         return publisher;
     }
 
-    public Result setPublisher(Field<String> publisher) {
+    public T setPublisher(Field<String> publisher) {
         this.publisher = publisher;
-        return this;
+        return self();
     }
 
     public Field<String> getEmbargoenddate() {
         return embargoenddate;
     }
 
-    public Result setEmbargoenddate(Field<String> embargoenddate) {
+    public T setEmbargoenddate(Field<String> embargoenddate) {
         this.embargoenddate = embargoenddate;
-        return this;
+        return self();
     }
 
     public List<Field<String>> getSource() {
         return source;
     }
 
-    public Result setSource(List<Field<String>> source) {
+    public T setSource(List<Field<String>> source) {
         this.source = source;
-        return this;
+        return self();
     }
 
     public List<Field<String>> getFulltext() {
         return fulltext;
     }
 
-    public Result setFulltext(List<Field<String>> fulltext) {
+    public T setFulltext(List<Field<String>> fulltext) {
         this.fulltext = fulltext;
-        return this;
+        return self();
     }
 
     public List<Field<String>> getFormat() {
         return format;
     }
 
-    public Result setFormat(List<Field<String>> format) {
+    public T setFormat(List<Field<String>> format) {
         this.format = format;
-        return this;
+        return self();
     }
 
     public List<Field<String>> getContributor() {
         return contributor;
     }
 
-    public Result setContributor(List<Field<String>> contributor) {
+    public T setContributor(List<Field<String>> contributor) {
         this.contributor = contributor;
-        return this;
+        return self();
     }
 
     public Qualifier getResourcetype() {
         return resourcetype;
     }
 
-    public Result setResourcetype(Qualifier resourcetype) {
+    public T setResourcetype(Qualifier resourcetype) {
         this.resourcetype = resourcetype;
-        return this;
+        return self();
     }
 
     public List<Field<String>> getCoverage() {
         return coverage;
     }
 
-    public Result setCoverage(List<Field<String>> coverage) {
+    public T setCoverage(List<Field<String>> coverage) {
         this.coverage = coverage;
-        return this;
+        return self();
     }
 
     public Field<String> getRefereed() {
         return refereed;
     }
 
-    public Result setRefereed(Field<String> refereed) {
+    public T setRefereed(Field<String> refereed) {
         this.refereed = refereed;
-        return this;
+        return self();
     }
 
     public List<Context> getContext() {
         return context;
     }
 
-    public Result setContext(List<Context> context) {
+    public T setContext(List<Context> context) {
         this.context = context;
-        return this;
+        return self();
     }
 
     public List<ExternalReference> getExternalReference() {
         return externalReference;
     }
 
-    public Result setExternalReference(List<ExternalReference> externalReference) {
+    public T setExternalReference(List<ExternalReference> externalReference) {
         this.externalReference = externalReference;
-        return this;
+        return self();
     }
 
     public List<Instance> getInstance() {
         return instance;
     }
 
-    public Result setInstance(List<Instance> instance) {
+    public T setInstance(List<Instance> instance) {
         this.instance = instance;
-        return this;
+        return self();
     }
 }
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Software.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Software.java
index 451efb99a..26c673d14 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Software.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Software.java
@@ -3,7 +3,7 @@ package eu.dnetlib.dhp.schema.oaf;
 import java.io.Serializable;
 import java.util.List;
 
-public class Software extends Result implements Serializable {
+public class Software extends Result<Software> implements Serializable {
 
     private List<Field<String>> documentationUrl;
 
@@ -48,4 +48,9 @@ public class Software extends Result implements Serializable {
         this.programmingLanguage = programmingLanguage;
         return this;
     }
+
+    @Override
+    protected Software self() {
+        return this;
+    }
 }