diff -r a2342f26c9de -r b0b56e0f8c7f server/src/app/Models/Document.php
--- a/server/src/app/Models/Document.php	Fri Jan 15 15:27:56 2016 +0100
+++ b/server/src/app/Models/Document.php	Fri Jan 15 15:35:00 2016 +0100
@@ -28,10 +28,12 @@
     // memoization
     private $providedCHO = null;
     private $title = false;
+    private $lang = null;
     private $publishers = null;
     private $mediaArray = null;
     private $issued = null;
     private $modified = null;
+    private $contributors = null;
 
     public function getProvidedCHO() {
         if(is_null($this->providedCHO)) {
@@ -43,10 +45,12 @@
     private function clearMemoizationCache() {
         $this->providedCHO = null;
         $this->title = false;
+        $this->lang = null;
         $this->publishers = null;
         $this->mediaArray = null;
         $this->issued = null;
         $this->modified = null;
+        $this->contributors = null;
     }
 
     public function getId() {
@@ -56,6 +60,30 @@
         return $this->id;
     }
 
+    public function getLanguage() {
+        if(is_null($this->lang)) {
+            try {
+                $langs = $this->getProvidedCHO()->all('<http://purl.org/dc/elements/1.1/language>');
+                if(count($langs) > 0) {
+                    $this->lang = $langs[0];
+                }
+            } catch(\Exception $e) {
+                $this->lang = null;
+            }
+        }
+        return $this->lang;
+    }
+
+    public function getLanguageValue() {
+        $lang = $this->getLanguage();
+        if($lang instanceof Resource) {
+            return $lang->getUri();
+        } else if($lan instanceof Literal) {
+            return $lang->getValue();
+        }
+        return null;
+    }
+
     public function getTitle() {
         if($this->title === false) {
             try {
@@ -67,6 +95,16 @@
         return $this->title;
     }
 
+    public function setTitle($value, $lang="fr") {
+        $oldTitle = $this->getTitle();
+        if($oldTitle && $oldTitle->getValue() != $value && $oldTitle->getLang() != $lang) {
+            $literalTitle = new Literal($value, $lang, null);
+            $this->setSimpleProperty($this->getProvidedCHO(), 'http://purl.org/dc/elements/1.1/title', $oldTitle, $literalTitle);
+            //clear cache
+            $this->title = false;
+        }
+    }
+
     public function getTitleValue() {
         $title = $this->getTitle();
         return is_null($title)?null:$title->getValue();
@@ -118,6 +156,17 @@
         return is_null($modified)?null:$modified->getValue();
     }
 
+    public function setModified($value) {
+        $modified = $this->getModified();
+        if($value && (!$modified || $modified->getValue() != $value) ) {
+
+            $newModified = new Literal($value, "http://purl.org/dc/terms/W3CDTF");
+            $this->setSimpleProperty($this->getProvidedCHO(), 'http://purl.org/dc/terms/modified', $modified, $newModified);
+
+            $this->modified = null;
+        }
+    }
+
     public function getMediaArray() {
 
         if(is_null($this->mediaArray)) {
@@ -163,25 +212,66 @@
     }
 
     public function getContributors() {
-        return array_reduce(
-            CocoonUtils::OLAC_ROLES,
-            function($res, $olacRole) {
-                return array_merge(
-                    $res,
-                    array_map(
-                        function($olacValue) use ($olacRole) {
-                            return [
-                                'name' => ($olacValue instanceof Literal)?$olacValue->getValue():null,
-                                'url' => ($olacValue instanceof Resource)?$olacValue->getUri():null,
-                                'role' => $olacRole
-                            ];
-                        },
-                        $this->getProvidedCHO()->all("<$olacRole>")
-                    )
-                );
-            },
-            []
-        );
+        if(is_null($this->contributors)) {
+            $this->contributors = array_reduce(
+                CocoonUtils::OLAC_ROLES,
+                function($res, $olacRole) {
+                    return array_merge(
+                        $res,
+                        array_map(
+                            function($olacValue) use ($olacRole) {
+                                return [
+                                    'name' => ($olacValue instanceof Literal)?$olacValue->getValue():null,
+                                    'nameLiteral' => ($olacValue instanceof Literal)?$olacValue:null,
+                                    'url' => ($olacValue instanceof Resource)?$olacValue->getUri():null,
+                                    'role' => $olacRole
+                                ];
+                            },
+                            $this->getProvidedCHO()->all("<$olacRole>")
+                        )
+                    );
+                },
+                []
+            );
+        }
+        return $this->contributors;
+    }
+
+    /**
+     * change contributors list
+     */
+    public function setContributors($contributors) {
+        $delta = $this->startDelta();
+        //remove old,
+        foreach ($this->getContributors() as $contribDef) {
+            $value = null;
+            if (is_null($contribDef['url'])) {
+                if(is_null($contribDef['nameLiteral'])) {
+                    $value = new Literal($contribDef['name']);
+                } else {
+                    $value = $contribDef['nameLiteral'];
+                }
+            } else {
+                $value = new Resource($contribDef['url']);
+            }
+            $this->getProvidedCHO()->delete($contribDef['role'], $value);
+            $delta->getDeletedGraph()->add($this->getProvidedCHO(), $contribDef['role'], $value);
+        }
+
+        //put new
+        foreach ($contributors as $newContribDef) {
+            $value = null;
+            if (is_null($newContribDef['url'])) {
+                $value = new Literal($newContribDef['name'], "fr", null);
+            } else {
+                $value = new Resource($newContribDef['url']);
+            }
+            $this->getProvidedCHO()->add($newContribDef['role'], $value);
+            $delta->getAddedGraph()->add($this->getProvidedCHO(), $newContribDef['role'], $value);
+        }
+
+        $this->contributors = null;
+
     }
 
     /**
@@ -240,13 +330,19 @@
                 $this->getPublishers()
             );
 
+            $contributors = array_map(
+                function($c) { unset($c['nameLiteral']); return $c; },
+                $this->getContributors()
+            );
+
             return [
                 'id' => $this->getId(),
                 'uri' => $this->getUri(),
                 'title' => $this->getTitleValue(),
+                'language' => $this->getLanguageValue(),
                 'modified' => $this->getModifiedValue(),
                 'publishers' => $publishers,
-                'contributors' => $this->getContributors(),
+                'contributors' => $contributors,
                 'mediaArray'=> $mediaArray
             ];
         }