@Entity
class ScrapBook{
   @Id@GeneratedValue(strategy=GenerationType.IDENTITY)
   int id;
   @OneToMany(mappedBy="scrapBook", fetch=FetchType.LAZY) 
   List<PageSet> pageSet;
}

@Entity
class PageSet{
   @Id@GeneratedValue(strategy=GenerationType.IDENTITY)
   int id;
   @ManyToOne( cascade={CascadeType.ALL})
   ScrapBook scrapBook;
   @OneToOne@JoinColumn(name="id", unique=false, nullable=true)
   LandscapePage landscapePage;
   @OneToOne@JoinColumn(name="id", unique=false, nullable=true)
   PortraitPage     portraitPage;
}

@MappedSuperclass
class Page{
   @Id@GeneratedValue(strategy=GenerationType.IDENTITY)
   id;
   @ManyToOne( cascade={CascadeType.ALL})
   PageSet pageSet;
   @OneToMany(mappedBy="page", fetch=FetchType.LAZY) 
   List<Photo> photos;
}

@Entity
class LandscapePage extends Page{}

@Entity
class PortraitPage extends Page{}

@Entity
class Photo{
   @Id@GeneratedValue(strategy=GenerationType.IDENTITY)
   int id;
   @ManyToOne( cascade={CascadeType.ALL})
   Page page;
}