diff --git a/YACOSCore/ejbModule/org/yacos/core/article/Article.java b/YACOSCore/ejbModule/org/yacos/core/article/Article.java
index 0f82e78..519ad57 100644
--- a/YACOSCore/ejbModule/org/yacos/core/article/Article.java
+++ b/YACOSCore/ejbModule/org/yacos/core/article/Article.java
@@ -3,6 +3,8 @@ package org.yacos.core.article;
 import java.io.Serializable;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.List;
+
 import javax.persistence.Entity;
 import javax.persistence.GeneratedValue;
 import javax.persistence.GenerationType;
@@ -77,15 +79,18 @@ public class Article implements Serializable {
 
 	public Article(int reference, String title, String topic,
 			String url_article, String mainAuthor,
-			ArrayList<String> secondaryAuthor, int state) {
+			List<String> secondaryAuthor, int state) {
 		//this.id = reference;
 		this.title = title;
 		this.topic = topic;
 		this.URL_article = url_article;
 		this.mainAuthor = mainAuthor;
-		this.secondaryAuthors = secondaryAuthor;
+		if(secondaryAuthor != null){
+			this.secondaryAuthors = new ArrayList<String>(secondaryAuthor);
+		} else {
+			this.secondaryAuthors = new ArrayList<String>();
+		}
 		this.state = state;
-		secondaryAuthors = new ArrayList<String>();
 		referees = new ArrayList<User>();
 		pcMembers = new ArrayList<User>();
 	}
diff --git a/YACOSCore/ejbModule/org/yacos/core/article/ArticleManagerBean.java b/YACOSCore/ejbModule/org/yacos/core/article/ArticleManagerBean.java
index 9a50181..03f250f 100644
--- a/YACOSCore/ejbModule/org/yacos/core/article/ArticleManagerBean.java
+++ b/YACOSCore/ejbModule/org/yacos/core/article/ArticleManagerBean.java
@@ -71,7 +71,6 @@ public class ArticleManagerBean implements IArticleManager, Serializable {
 		return (List<User>) article.getReferees();
 	}
 
-	
 	public Preference getArticlePreferenceForUser(Article article,
 			String pcMemberLogin) {
 		Query query = em.createQuery("SELECT p FROM Preference p WHERE p.article.id = :articleid AND p.pcMember.id = :pcmemberlogin");
@@ -102,13 +101,30 @@ public class ArticleManagerBean implements IArticleManager, Serializable {
 		User pcMember = em.find(User.class, userLogin);
 		preference.setPcMember(pcMember);
 		preference.setPreference(preferenceValue);
-		//c'est mal !!!
-		// FIXME 
 		em.persist(preference);
 	}
 	
+	public void addOrUpdatePreference(Preference preference){
+		if(existsPreference(preference)){
+			updatePreference(preference);
+		} else {
+			addArticlePreference(preference);
+		}
+	}
+	
+	public void updatePreference(Preference preference){
+		em.merge(preference);
+	}
+
+	public boolean existsArticle(Article article) {
+		return em.find(Article.class, article.getId())!=null;
+	}
+
+	public boolean existsPreference(Preference preference) {
+		return em.find(Preference.class, preference.getId())!=null;
+	}
+	
 	public EntityManager getEntityManager() {
 		return em;
 	}
-	
 }
diff --git a/YACOSCore/ejbModule/org/yacos/core/article/IArticleManager.java b/YACOSCore/ejbModule/org/yacos/core/article/IArticleManager.java
index 366b4ea..b56917e 100644
--- a/YACOSCore/ejbModule/org/yacos/core/article/IArticleManager.java
+++ b/YACOSCore/ejbModule/org/yacos/core/article/IArticleManager.java
@@ -16,6 +16,9 @@ public interface IArticleManager {
 	public Preference getArticlePreferenceForUser(Article article, String pcMemberLogin);
 	public void setArticlePreferences(Article article, List<Preference> preferences);
 	public void addArticlePreference(Integer article_id, String userLogin, String preferenceValue);
+	public void addOrUpdatePreference(Preference preference);
+	public boolean existsArticle(Article article);
+	public boolean existsPreference(Preference preference);
 	
 	public List<Article> getArticles();
 	
diff --git a/YACOSCore/ejbModule/org/yacos/core/article/Preference.java b/YACOSCore/ejbModule/org/yacos/core/article/Preference.java
index 7c4f107..34d041e 100644
--- a/YACOSCore/ejbModule/org/yacos/core/article/Preference.java
+++ b/YACOSCore/ejbModule/org/yacos/core/article/Preference.java
@@ -77,6 +77,13 @@ public class Preference implements Serializable {
 	public void setPreference(String preference) {
 		this.preference = preference;
 	}
+	
+	public PreferencePK getId(){
+		PreferencePK id = new PreferencePK();
+		id.setArticle(this.article);
+		id.setPcMember(this.pcMember);
+		return id;
+	}
 }
 
 
diff --git a/YACOSCore/ejbModule/org/yacos/core/conferences/Conference.java b/YACOSCore/ejbModule/org/yacos/core/conferences/Conference.java
index b320066..b0e0fff 100644
--- a/YACOSCore/ejbModule/org/yacos/core/conferences/Conference.java
+++ b/YACOSCore/ejbModule/org/yacos/core/conferences/Conference.java
@@ -1,173 +1,172 @@
-package org.yacos.core.conferences;
-
-import java.io.Serializable;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Date;
-
-import javax.persistence.Entity;
-import javax.persistence.GeneratedValue;
-import javax.persistence.GenerationType;
-import javax.persistence.Id;
-import javax.persistence.OneToMany;
-import javax.persistence.Temporal;
-import javax.persistence.TemporalType;
-
-import org.yacos.core.article.Article;
-import org.yacos.core.users.Role;
-
-
-@Entity
-public class Conference implements Serializable{
-	
-	private static final long serialVersionUID = 1L;
-	
-	@Id
-	@GeneratedValue(strategy=GenerationType.AUTO)
-	private Integer id;
-	private String titre;
-	private String description;
-	private String otherInformations;
-	@Temporal(TemporalType.DATE)
-	private Date dateAbstract;
-	@Temporal(TemporalType.DATE)
-	private Date dateArticle;
-	@Temporal(TemporalType.DATE)
-	private Date dateEvaluation;
-	@Temporal(TemporalType.DATE)
-	private Date dateStart;
-	@Temporal(TemporalType.DATE)
-	private Date dateEnd;
-	
-	/**
-	 * Roles of users for this conference 
-	 */
-	@OneToMany(targetEntity=Role.class,mappedBy="conference")
-	private Collection<Role> roles;
-	
-	/*@OneToOne(targetEntity=User.class,optional=true)
-	@JoinColumn(name="chairman_id",nullable=true)
-	private User chairman;
-	*/
-	@OneToMany(targetEntity=Article.class,mappedBy="conference")
-	private Collection<Article> articles;
-
-	/**
-	 * @return the chairman
-	 */
-	/*@OneToOne(targetEntity=User.class,optional=true)
-	@JoinColumn(name="chairman_id",nullable=true)
-	public User getChairman() {
-		return chairman;
-	}
-*/
-	/**
-	 * @param chairman the chairman to set
-	 */
-	/*
-	@OneToOne(targetEntity=User.class,optional=true)
-	@JoinColumn(name="chairman_id",nullable=true)
-	public void setChairman(User chairman) {
-		this.chairman = chairman;
-	}
-	*/
-	@Temporal(TemporalType.DATE)
-    public Date getDataAbstract() {
-		return dateAbstract;
-	}
-
-	@Temporal(TemporalType.DATE)
-	public void setDataAbstract(Date dataAbstract) {
-		this.dateAbstract = dataAbstract;
-	}
-	@Temporal(TemporalType.DATE)
-	public Date getDateArticle() {
-		return dateArticle;
-	}
-	@Temporal(TemporalType.DATE)
-	public void setDateArticle(Date dateArticle) {
-		this.dateArticle = dateArticle;
-	}
-	@Temporal(TemporalType.DATE)
-	public Date getDateEnd() {
-		return dateEnd;
-	}
-	@Temporal(TemporalType.DATE)
-	public void setDateEnd(Date dateEnd) {
-		this.dateEnd = dateEnd;
-	}
-	@Temporal(TemporalType.DATE)
-	public Date getDateEvaluation() {
-		return dateEvaluation;
-	}
-	@Temporal(TemporalType.DATE)
-	public void setDateEvaluation(Date dateEvaluation) {
-		this.dateEvaluation = dateEvaluation;
-	}
-	@Temporal(TemporalType.DATE)
-	public Date getDateStart() {
-		return dateStart;
-	}
-	@Temporal(TemporalType.DATE)
-	public void setDateStart(Date dateStart) {
-		this.dateStart = dateStart;
-	}
-	public String getDescription() {
-		return description;
-	}
-	public void setDescription(String descirption) {
-		this.description = descirption;
-	}
-	public String getOtherInformations() {
-		return otherInformations;
-	}
-	public void setOtherInformations(String otherInformations) {
-		this.otherInformations = otherInformations;
-	}
-	public String getTitre() {
-		return titre;
-	}
-	public void setTitre(String titre) {
-		this.titre = titre;
-	}
-	public Integer getId() {
-		return id;
-	}
-	public void setId(Integer id) {
-		this.id = id;
-	}
-	
-	public Conference() {
-		this.roles = new ArrayList<Role>();
-	}
-	
-	public Conference(String titre, String descirption, String infoComplementray, Date dataAbstract, Date dateArticle, Date dateEvaluation, Date dateStart, Date dateEnd) {
-		this();
-		this.titre = titre;
-		this.description = descirption;
-		this.otherInformations = infoComplementray;
-		this.dateAbstract = dataAbstract;
-		this.dateArticle = dateArticle;
-		this.dateEvaluation = dateEvaluation;
-		this.dateStart = dateStart;
-		this.dateEnd = dateEnd;
-	}
-
-	@OneToMany(targetEntity=Article.class,mappedBy="articles")
-	public void setArticles(Collection<Article> articles) {
-		this.articles = articles;
-	}
-	
-	@OneToMany(targetEntity=Article.class,mappedBy="articles")
-	public Collection<Article> getArticles() {
-		return articles;
-	}
-
-	public Collection<Role> getRoles() {
-		return roles;
-	}
-
-	public void setRoles(Collection<Role> roles) {
-		this.roles = roles;
-	}
-}
+package org.yacos.core.conferences;
+
+import java.io.Serializable;
+import java.util.Collection;
+import java.util.Date;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+import javax.persistence.OneToMany;
+import javax.persistence.Temporal;
+import javax.persistence.TemporalType;
+
+import org.yacos.core.article.Article;
+import org.yacos.core.users.Role;
+
+
+@Entity
+public class Conference implements Serializable{
+	
+	private static final long serialVersionUID = 1L;
+	
+	@Id
+	@GeneratedValue(strategy=GenerationType.AUTO)
+	private Integer id;
+	private String titre;
+	private String description;
+	private String otherInformations;
+	@Temporal(TemporalType.DATE)
+	private Date dateAbstract;
+	@Temporal(TemporalType.DATE)
+	private Date dateArticle;
+	@Temporal(TemporalType.DATE)
+	private Date dateEvaluation;
+	@Temporal(TemporalType.DATE)
+	private Date dateStart;
+	@Temporal(TemporalType.DATE)
+	private Date dateEnd;
+	
+	/**
+	 * Roles of users for this conference 
+	 */
+	@OneToMany(targetEntity=Role.class,mappedBy="conference")
+	private Collection<Role> roles;
+	
+	/*@OneToOne(targetEntity=User.class,optional=true)
+	@JoinColumn(name="chairman_id",nullable=true)
+	private User chairman;
+	*/
+	@OneToMany(targetEntity=Article.class,mappedBy="conference")
+	private Collection<Article> articles;
+
+	/**
+	 * @return the chairman
+	 */
+	/*@OneToOne(targetEntity=User.class,optional=true)
+	@JoinColumn(name="chairman_id",nullable=true)
+	public User getChairman() {
+		return chairman;
+	}
+*/
+	/**
+	 * @param chairman the chairman to set
+	 */
+	/*
+	@OneToOne(targetEntity=User.class,optional=true)
+	@JoinColumn(name="chairman_id",nullable=true)
+	public void setChairman(User chairman) {
+		this.chairman = chairman;
+	}
+	*/
+	@Temporal(TemporalType.DATE)
+    public Date getDataAbstract() {
+		return dateAbstract;
+	}
+
+	@Temporal(TemporalType.DATE)
+	public void setDataAbstract(Date dataAbstract) {
+		this.dateAbstract = dataAbstract;
+	}
+	@Temporal(TemporalType.DATE)
+	public Date getDateArticle() {
+		return dateArticle;
+	}
+	@Temporal(TemporalType.DATE)
+	public void setDateArticle(Date dateArticle) {
+		this.dateArticle = dateArticle;
+	}
+	@Temporal(TemporalType.DATE)
+	public Date getDateEnd() {
+		return dateEnd;
+	}
+	@Temporal(TemporalType.DATE)
+	public void setDateEnd(Date dateEnd) {
+		this.dateEnd = dateEnd;
+	}
+	@Temporal(TemporalType.DATE)
+	public Date getDateEvaluation() {
+		return dateEvaluation;
+	}
+	@Temporal(TemporalType.DATE)
+	public void setDateEvaluation(Date dateEvaluation) {
+		this.dateEvaluation = dateEvaluation;
+	}
+	@Temporal(TemporalType.DATE)
+	public Date getDateStart() {
+		return dateStart;
+	}
+	@Temporal(TemporalType.DATE)
+	public void setDateStart(Date dateStart) {
+		this.dateStart = dateStart;
+	}
+	public String getDescription() {
+		return description;
+	}
+	public void setDescription(String descirption) {
+		this.description = descirption;
+	}
+	public String getOtherInformations() {
+		return otherInformations;
+	}
+	public void setOtherInformations(String otherInformations) {
+		this.otherInformations = otherInformations;
+	}
+	public String getTitre() {
+		return titre;
+	}
+	public void setTitre(String titre) {
+		this.titre = titre;
+	}
+	public Integer getId() {
+		return id;
+	}
+	public void setId(Integer id) {
+		this.id = id;
+	}
+	
+	public Conference() {
+		this.roles = new ArrayList<Role>();
+	}
+	
+	public Conference(String titre, String descirption, String infoComplementray, Date dataAbstract, Date dateArticle, Date dateEvaluation, Date dateStart, Date dateEnd) {
+		this();
+		this.titre = titre;
+		this.description = descirption;
+		this.otherInformations = infoComplementray;
+		this.dateAbstract = dataAbstract;
+		this.dateArticle = dateArticle;
+		this.dateEvaluation = dateEvaluation;
+		this.dateStart = dateStart;
+		this.dateEnd = dateEnd;
+	}
+
+	@OneToMany(targetEntity=Article.class,mappedBy="articles")
+	public void setArticles(Collection<Article> articles) {
+		this.articles = articles;
+	}
+	
+	@OneToMany(targetEntity=Article.class,mappedBy="articles")
+	public Collection<Article> getArticles() {
+		return articles;
+	}
+
+	public Collection<Role> getRoles() {
+		return roles;
+	}
+
+	public void setRoles(Collection<Role> roles) {
+		this.roles = roles;
+	}
+}
diff --git a/YACOSCore/ejbModule/org/yacos/core/users/IUserManager.java b/YACOSCore/ejbModule/org/yacos/core/users/IUserManager.java
index 3b07cda..17ac85e 100644
--- a/YACOSCore/ejbModule/org/yacos/core/users/IUserManager.java
+++ b/YACOSCore/ejbModule/org/yacos/core/users/IUserManager.java
@@ -13,6 +13,6 @@ public interface IUserManager {
 	public void removeUser(User user);
 	public User getUser(String login);
 	public void UpdateUser(User user);
-	public Boolean existe(User user);
+	public Boolean exists(User user);
 
 }
diff --git a/YACOSCore/ejbModule/org/yacos/core/users/UserManagerBean.java b/YACOSCore/ejbModule/org/yacos/core/users/UserManagerBean.java
index 5401e0a..56c82c2 100644
--- a/YACOSCore/ejbModule/org/yacos/core/users/UserManagerBean.java
+++ b/YACOSCore/ejbModule/org/yacos/core/users/UserManagerBean.java
@@ -33,7 +33,7 @@ public class UserManagerBean implements IUserManager{
 	 * @param user
 	 */
 	public void addUser(User user) throws PKAlreadyUsedException{
-		if (!this.existe(user)){
+		if (!this.exists(user)){
 			em.persist(user);
 		}
 		else{
@@ -58,7 +58,7 @@ public class UserManagerBean implements IUserManager{
 		em.merge(user);
 	}
 	
-	public Boolean existe(User user){
+	public Boolean exists(User user){
 	  return (this.getUser(user.getLogin())!= null); 
 	}