public interface APEObject
{
    public Long getId();
    public void setId(Long id);
}

@Entity
public class APEObjectWithSystemProperties implements APEObject
{
    @Id
    private Long id;

    public Long getId()
    {
        return this.id;
    }
    public void setId(Long id)
    {
        this.id = id;
    }
}

@Entity
public class Article extends APEObjectWithSystemProperties
{
    // Nothing do here
}

@Entity
public class EmbeddedObject extends APEObject
{
    public Long getId()
    {
        return null;
    }
    public void setId(Long id)
    {
        // Empty block
    }
}