@Entity
@NamedQueries( {
      @NamedQuery(name = "getClassificationStatistics",
                query = "select c.classification as label, count(*) as numberOfPaper " +
                      "from Classification c " +
                      "where c.article.year between :firstYear and :lastYear " +
                      "group by c.classification " +
                      "order by c.classification"),
      @NamedQuery(name = "getClassificationFromArticle",
                query = "from Classification c where c.article = :article") })
public class Classification {
   @Id
   @GeneratedValue
   private long identifier;
   
   @OneToOne
   Article article;
   
   String classification;

@Entity
@Table(name = "ARTICLES")
public class Article {
   @Id
   @GeneratedValue
   @Column(name = "ArticleId")
   private long identifier;

   private String title;

   @Type(type = "text")
   private String articleAbstract;

   private int year;

   @Lob
   private byte[] fullTextPdf;

   @ManyToOne
   private Journal journal;

   @ManyToMany
   @JoinTable(name = "Article_Author", joinColumns = { @JoinColumn(name = "ArticleId") }, inverseJoinColumns = { @JoinColumn(name = "AuthorId") })
   private List<Author> authors = new Vector<Author>();