diff --git a/main.go b/main.go
index 0a5ee67..1ca0b4d 100644
--- a/main.go
+++ b/main.go
@@ -38,8 +38,12 @@ func main() {
 	articleService := &article.Service{DB: db}
 
 	// 4. wire services
-	userService.Wire(server)
-	articleService.Wire(server)
+	if err = userService.Wire(server); err != nil {
+		log.Fatalf("/!\\ cannot wire service 'user': %s", err)
+	}
+	if err = articleService.Wire(server); err != nil {
+		log.Fatalf("/!\\ cannot wire service 'article': %s", err)
+	}
 
 	// 5. create http server
 	httpServer, err := server.ToHTTPServer()
diff --git a/service/article/article.go b/service/article/article.go
index 06dddf3..0e3fbd3 100644
--- a/service/article/article.go
+++ b/service/article/article.go
@@ -15,66 +15,87 @@ type Service struct {
 }
 
 // Wire services to their paths
-func (s Service) Wire(server *aicra.Server) {
+func (s Service) Wire(server *aicra.Server) error {
 	if !s.DB.HasTable(&model.Article{}) {
 		s.DB.CreateTable(&model.Article{})
 	}
 
-	server.Handle(http.MethodGet, "/articles", s.getAllArticles)
-	server.Handle(http.MethodGet, "/user/{id}/articles", s.getArticlesByAuthor)
-	server.Handle(http.MethodGet, "/article/{id}", s.getArticleByID)
-	server.Handle(http.MethodPost, "/article", s.postArticle)
-	server.Handle(http.MethodDelete, "/article/{id}", s.deleteArticle)
-}
-
-func (s Service) getArticlesByAuthor(req api.Request, res *api.Response) api.Error {
-	id, err := req.Param.GetUint("author_id")
-	if err != nil {
-		return api.ErrorInvalidParam
+	if err := server.Handle(http.MethodGet, "/articles", s.getAllArticles); err != nil {
+		return err
 	}
-	articles := make([]model.Article, 0)
-	s.DB.Where("author = ?", id).Find(&articles)
-	res.SetData("articles", articles)
-	return api.ErrorSuccess
+	if err := server.Handle(http.MethodGet, "/user/{id}/articles", s.getArticlesByAuthor); err != nil {
+		return err
+	}
+	if err := server.Handle(http.MethodGet, "/article/{id}", s.getArticleByID); err != nil {
+		return err
+	}
+	if err := server.Handle(http.MethodPost, "/article", s.postArticle); err != nil {
+		return err
+	}
+	if err := server.Handle(http.MethodDelete, "/article/{id}", s.deleteArticle); err != nil {
+		return err
+	}
+	return nil
 }
 
-func (s Service) getAllArticles(req api.Request, res *api.Response) api.Error {
+type iByID struct {
+	ID uint
+}
+
+type oArticle struct {
+	ID     uint
+	Author uint
+	Title  string
+	Body   string
+	Score  uint
+}
+type iCreate struct {
+	Title string
+	Body  string
+}
+
+type oArticleList struct {
+	Articles []model.Article
+}
+
+func (s Service) getArticlesByAuthor(param iByID) (*oArticleList, api.Error) {
+	articles := make([]model.Article, 0)
+	s.DB.Where("author = ?", param.ID).Find(&articles)
+	return &oArticleList{
+		Articles: articles,
+	}, api.ErrorSuccess
+}
+
+func (s Service) getAllArticles() (*oArticleList, api.Error) {
 	articles := make([]model.Article, 0)
 	s.DB.Find(&articles)
-	res.SetData("articles", articles)
-	return api.ErrorSuccess
+	return &oArticleList{
+		Articles: articles,
+	}, api.ErrorSuccess
 }
 
-func (s Service) getArticleByID(req api.Request, res *api.Response) api.Error {
-	id, err := req.Param.GetUint("article_id")
-	if err != nil {
-		return api.ErrorInvalidParam
-	}
-
+func (s Service) getArticleByID(param iByID) (*oArticle, api.Error) {
 	var article model.Article
-	if s.DB.First(&article, id).RecordNotFound() {
-		return api.ErrorNoMatchFound
+	if s.DB.First(&article, param.ID).RecordNotFound() {
+		return nil, api.ErrorNoMatchFound
 	}
 
-	res.SetData("id", article.ID)
-	res.SetData("title", article.Title)
-	res.SetData("body", article.Body)
-	res.SetData("author", article.Author)
-	return api.ErrorSuccess
+	return &oArticle{
+		ID:     article.ID,
+		Title:  article.Title,
+		Body:   article.Body,
+		Author: article.Author,
+	}, api.ErrorSuccess
 }
 
-func (s Service) postArticle(req api.Request, res *api.Response) api.Error {
-	return api.ErrorNotImplemented
+func (s Service) postArticle(param iCreate) (*oArticle, api.Error) {
+	return nil, api.ErrorNotImplemented
 }
 
-func (s Service) deleteArticle(req api.Request, res *api.Response) api.Error {
-	id, err := req.Param.GetUint("user_id")
-	if err != nil {
-		return api.ErrorInvalidParam
+func (s Service) deleteArticle(param iByID) api.Error {
+	article := model.Article{
+		ID: param.ID,
 	}
-
-	article := model.Article{}
-	article.ID = id
 	s.DB.Delete(&article)
 
 	return api.ErrorSuccess
diff --git a/service/user/user.go b/service/user/user.go
index 6f7b14a..9051be6 100644
--- a/service/user/user.go
+++ b/service/user/user.go
@@ -15,109 +15,132 @@ type Service struct {
 }
 
 // Wire services to their paths
-func (s Service) Wire(server *aicra.Server) {
+func (s Service) Wire(server *aicra.Server) error {
 	if !s.DB.HasTable(&model.User{}) {
 		s.DB.CreateTable(&model.User{})
 	}
 
-	server.Handle(http.MethodGet, "/users", s.getAllUsers)
-	server.Handle(http.MethodGet, "/user/{id}", s.getUserByID)
-	server.Handle(http.MethodPost, "/user", s.createUser)
-	server.Handle(http.MethodPut, "/user/{id}", s.updateUser)
-	server.Handle(http.MethodDelete, "/user/{id}", s.deleteUser)
-}
-
-func (s Service) getAllUsers(req api.Request, res *api.Response) api.Error {
-	users := make([]model.User, 0)
-	s.DB.Find(&users)
-	res.SetData("users", users)
-	return api.ErrorSuccess
-}
-func (s Service) getUserByID(req api.Request, res *api.Response) api.Error {
-	id, err := req.Param.GetUint("user_id")
-	if err != nil {
-		return api.ErrorInvalidParam
+	if err := server.Handle(http.MethodGet, "/user/{id}", s.getUserByID); err != nil {
+		return err
 	}
+	if err := server.Handle(http.MethodGet, "/users", s.getAllUsers); err != nil {
+		return err
+	}
+	if err := server.Handle(http.MethodPost, "/user", s.createUser); err != nil {
+		return err
+	}
+	if err := server.Handle(http.MethodPut, "/user/{id}", s.updateUser); err != nil {
+		return err
+	}
+	if err := server.Handle(http.MethodDelete, "/user/{id}", s.deleteUser); err != nil {
+		return err
+	}
+	return nil
+}
 
+type oUserList struct {
+	Users []model.User
+}
+
+type oUser struct {
+	ID        uint
+	Username  string
+	Firstname string
+	Lastname  string
+	Articles  interface{}
+}
+type iByID struct {
+	ID uint
+}
+
+type iCreate struct {
+	Username  string
+	Firstname string
+	Lastname  string
+}
+type iUpdate struct {
+	ID        uint
+	Username  *string
+	Firstname *string
+	Lastname  *string
+}
+
+func (s Service) getAllUsers() (*oUserList, api.Error) {
+	users := oUserList{}
+	s.DB.Find(&users.Users)
+	return &users, api.ErrorSuccess
+}
+func (s Service) getUserByID(param iByID) (*oUser, api.Error) {
 	var user model.User
-	if s.DB.First(&user, id).RecordNotFound() {
-		return api.ErrorNoMatchFound
+	if s.DB.First(&user, param.ID).RecordNotFound() {
+		return nil, api.ErrorNoMatchFound
 	}
 
-	res.SetData("id", user.ID)
-	res.SetData("username", user.Username)
-	res.SetData("firstname", user.Firstname)
-	res.SetData("lastname", user.Lastname)
-	res.SetData("articles", user.Articles)
-	return api.ErrorSuccess
+	return &oUser{
+		ID:        user.ID,
+		Username:  user.Username,
+		Firstname: user.Firstname,
+		Lastname:  user.Lastname,
+		Articles:  user.Articles,
+	}, api.ErrorSuccess
 }
 
-func (s Service) createUser(req api.Request, res *api.Response) api.Error {
-	var user model.User
-	var err error
-	user.Username, err = req.Param.GetString("username")
-	if err != nil {
-		return api.ErrorInvalidParam
-	}
-	user.Firstname, err = req.Param.GetString("firstname")
-	if err != nil {
-		return api.ErrorInvalidParam
-	}
-	user.Lastname, err = req.Param.GetString("lastname")
-	if err != nil {
-		return api.ErrorInvalidParam
+func (s Service) createUser(param iCreate) (*oUser, api.Error) {
+	user := model.User{
+		Username:  param.Username,
+		Firstname: param.Firstname,
+		Lastname:  param.Lastname,
 	}
 
 	s.DB.Create(&user)
 	if s.DB.Last(&user).RecordNotFound() {
-		return api.ErrorNoMatchFound
+		return nil, api.ErrorNoMatchFound
 	}
 
-	res.SetData("id", user.ID)
-	res.SetData("username", user.Username)
-	res.SetData("firstname", user.Firstname)
-	res.SetData("lastname", user.Lastname)
-	res.SetData("articles", user.Articles)
-	return api.ErrorSuccess
+	return &oUser{
+		ID:        user.ID,
+		Username:  user.Username,
+		Firstname: user.Firstname,
+		Lastname:  user.Lastname,
+		Articles:  user.Articles,
+	}, api.ErrorSuccess
 }
 
-func (s Service) updateUser(req api.Request, res *api.Response) api.Error {
-	id, err := req.Param.GetUint("user_id")
-	if err != nil {
-		return api.ErrorInvalidParam
-	}
-
+func (s Service) updateUser(param iUpdate) (*oUser, api.Error) {
 	var user model.User
-	if s.DB.First(&user, id).RecordNotFound() {
-		return api.ErrorNoMatchFound
+	if s.DB.First(&user, param.ID).RecordNotFound() {
+		return nil, api.ErrorNoMatchFound
 	}
 
 	// override with updated values
-	if updated, err := req.Param.GetString("username"); err == nil {
-		user.Username = updated
+	if param.Username != nil {
+		user.Username = *param.Username
 	}
-	if updated, err := req.Param.GetString("firstname"); err == nil {
-		user.Firstname = updated
+	if param.Firstname != nil {
+		user.Firstname = *param.Firstname
 	}
-	if updated, err := req.Param.GetString("lastname"); err == nil {
-		user.Lastname = updated
+	if param.Lastname != nil {
+		user.Lastname = *param.Lastname
 	}
 
 	// update
 	if s.DB.Save(&user).RowsAffected < 1 {
-		return api.ErrorFailure
+		return nil, api.ErrorFailure
 	}
-	return api.ErrorSuccess
+
+	return &oUser{
+		ID:        user.ID,
+		Username:  user.Username,
+		Firstname: user.Firstname,
+		Lastname:  user.Lastname,
+		Articles:  user.Articles,
+	}, api.ErrorSuccess
 }
 
-func (s Service) deleteUser(req api.Request, res *api.Response) api.Error {
-	id, err := req.Param.GetUint("user_id")
-	if err != nil {
-		return api.ErrorInvalidParam
+func (s Service) deleteUser(param iByID) api.Error {
+	user := model.User{
+		ID: param.ID,
 	}
-
-	user := model.User{}
-	user.ID = id
 	s.DB.Delete(&user)
 	return api.ErrorSuccess
 }