Access to a child object attribute using jstl

i have an object called "Project" which have a lot of attributes and some of theme are objects i know that using

<jstl:out value="${project.id}"/>

i get the id of the object in the jsp page but if i want the id of and attribute object of "project" what should i write

to make it more clear here is my class project and it's class child

@Entity
@Table(name = "project")
public class Project {

    @Id
    @Column(name = "idSM")
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Integer projectId;

    @Column(name = "nom")
    private String nomproject;

    @ManyToOne
    @JoinColumn(name = "backlog")
    private Backlog bg;
    ....getter and setters...
}

i want to get the attributes of "bg" what should i write ?