Caused by: org.hibernate.HibernateException: Not all named super-types (extends) were found : [com.sample.model.Sample]
  at org.hibernate.boot.model.source.internal.hbm.EntityHierarchyBuilder.buildHierarchies(EntityHierarchyBuilder.java:76)
  at org.hibernate.boot.model.source.internal.hbm.HbmMetadataSourceProcessorImpl.<init>(HbmMetadataSourceProcessorImpl.java:66)

@Entity
@Table(name = "tbl_sample")
public class Sample extends Auditable {
  private Long id;
  @ManyToOne
  @JoinColumn(name = "relationA", nullable = true)
  private RelationA relationA;
  ... etc
}

@MappedSuperClass
public abstract class Auditable extends Persistable {
   //audit props
}

@MappedSuperClass
public abstract class Persistable {
   //common props
}


public class BloodSample extends Sample {
.....
}

BloodSample.hbm.xml 

<hibernate-mapping package="com.sample.model">  
  <joined-subclass name="BloodSample" table="tbl_blood_sample"
   extends="com.sample.model.Sample">
   <key column="ID" />

  <property name="sampleNo" column="sampleNo"/>
   etc....
 </joined-subclass>
</hibernate-mapping>