diff --git a/src/schema/Value.php b/src/schema/Value.php
index 02a8c54..bc8de23 100644
--- a/src/schema/Value.php
+++ b/src/schema/Value.php
@@ -35,7 +35,10 @@ abstract class Value implements ArrayAccess, IteratorAggregate {
   abstract function getType(): IType;
 
   /** retourner true si la valeur existe */
-  abstract function available(): bool;
+  abstract function isPresent(): bool;
+
+  /** retourner true si la valeur est disponible */
+  abstract function isAvailable(): bool;
 
   /** supprimer la valeur */
   abstract function unset(): void;
@@ -44,16 +47,16 @@ abstract class Value implements ArrayAccess, IteratorAggregate {
   abstract function set($value): self;
 
   /** obtenir le résultat de l'appel de la fonction {@link set()} */
-  abstract function result(): Result;
+  abstract function getResult(): Result;
 
   /** retourner true si la valeur est valide */
-  abstract function valid(): bool;
+  abstract function isValid(): bool;
 
   /** obtenir la valeur */
   abstract function get($default=null);
 
   /** retourner true si la valeur est dans sa forme normalisée */
-  abstract function normalized(): bool;
+  abstract function isNormalized(): bool;
 
   /** formatter la valeur pour affichage */
   abstract function format($format=null): string;
diff --git a/src/schema/_scalar/ScalarResult.php b/src/schema/_scalar/ScalarResult.php
index 44f07b9..e5c5419 100644
--- a/src/schema/_scalar/ScalarResult.php
+++ b/src/schema/_scalar/ScalarResult.php
@@ -9,15 +9,16 @@ use nur\sery\schema\ValueException;
 /**
  * Class ScalarResult: résultat de l'analyse ou de la normalisation d'une valeur
  *
- * @property bool $missing la valeur est-elle inexistante?
- * @property bool $null si elle existe, la valeur est-nulle?
- * @property bool $valid si elle existe, la valeur est-elle valide?
+ * @property bool $present la valeur existe-t-elle?
+ * @property bool $available si la valeur existe, est-elle disponible?
+ * @property bool $null si la valeur existe, est-elle nulle?
+ * @property bool $valid si la valeur existe, est-elle valide?
  * @property bool $normalized si la valeur est valide, est-elle normalisée?
  * @property string|null $orig valeur originale avant analyse avec parse()
  * @property string|null $message message si la valeur n'est pas valide
  */
 class ScalarResult extends Result {
-  const KEYS = ["missing", "null", "valid", "normalized", "orig", "message"];
+  const KEYS = ["present", "available", "null", "valid", "normalized", "orig", "message"];
 
   function isScalar(?ScalarResult &$scalar=null): bool { $scalar = $this; return true; }
 
@@ -36,7 +37,8 @@ class ScalarResult extends Result {
   function reset(): void {
     $this->result = array_merge(
       array_fill_keys(static::KEYS, null), [
-      "missing" => true,
+      "present" => false,
+      "available" => false,
       "null" => false,
       "valid" => false,
       "normalized" => false,
@@ -57,9 +59,10 @@ class ScalarResult extends Result {
   }
 
   function setMissing(ScalarSchema $schema): int {
-    $this->missing = true;
+    $this->present = false;
+    $this->available = false;
     if (!$schema->required) {
-      $this->null = true;
+      $this->null = false;
       $this->valid = true;
       $this->normalized = true;
       return ref_analyze::NORMALIZED;
@@ -71,8 +74,26 @@ class ScalarResult extends Result {
     }
   }
 
+  function setUnavailable(ScalarSchema $schema): int {
+    $this->present = true;
+    $this->available = false;
+    if (!$schema->required) {
+      $this->null = false;
+      $this->valid = true;
+      $this->normalized = true;
+      return ref_analyze::NORMALIZED;
+    } else {
+      $message = cl::get($schema->messages, "unavailable");
+      self::replace_key($message, $schema->name);
+      $this->message = $message;
+      return ref_analyze::UNAVAILABLE;
+    }
+  }
+
   function setNull(ScalarSchema $schema): int {
-    $this->missing = true;
+    $this->present = true;
+    $this->available = true;
+    $this->null = true;
     if ($schema->nullable) {
       $this->valid = true;
       $this->normalized = true;
diff --git a/src/schema/_scalar/ScalarValue.php b/src/schema/_scalar/ScalarValue.php
index c35d746..dcbbadb 100644
--- a/src/schema/_scalar/ScalarValue.php
+++ b/src/schema/_scalar/ScalarValue.php
@@ -61,23 +61,23 @@ class ScalarValue extends Value {
     $result = $this->result;
     $result->reset();
     #XXX résoudre le type
-    if (!$input->available()) return $result->setMissing($schema);
+    if (!$input->isAvailable()) return $result->setUnavailable($schema);
     $value = $input->get($destKey);
     if ($value === null) return $result->setNull($schema);
   }
 
-  function exists(): bool {
-    return $this->input->exits($this->destKey);
+  function isPresent(): bool {
+    return $this->input->isPresent($this->destKey);
   }
 
-  function available(): bool {
-    return $this->input->available($this->destKey);
+  function isAvailable(): bool {
+    return $this->input->isAvailable($this->destKey);
   }
 
   function get($default=null) {
     $destKey = $this->destKey;
     $input = $this->input;
-    if ($input->available($destKey)) return $input->get($destKey);
+    if ($input->isAvailable($destKey)) return $input->get($destKey);
     else return $default;
   }
 
@@ -92,10 +92,10 @@ class ScalarValue extends Value {
     return $this->type;
   }
 
-  function valid(): bool {
+  function isValid(): bool {
   }
 
-  function normalized(): bool {
+  function isNormalized(): bool {
   }
 
   /**
diff --git a/src/schema/input/FormInput.php b/src/schema/input/FormInput.php
index fcd0b22..0013d68 100644
--- a/src/schema/input/FormInput.php
+++ b/src/schema/input/FormInput.php
@@ -14,12 +14,12 @@ namespace nur\sery\schema\input;
 class FormInput extends Input {
   const ALLOW_EMPTY = false;
 
-  function exists($key=null): bool {
+  function isPresent($key=null): bool {
     if ($key === null) return false;
     return array_key_exists($key, $_POST) || array_key_exists($key, $_GET);
   }
 
-  function available($key=null): bool {
+  function isAvailable($key=null): bool {
     if ($key === null) return false;
     if (array_key_exists($key, $_POST)) {
       return $this->allowEmpty || $_POST[$key] !== "";
diff --git a/src/schema/input/GetInput.php b/src/schema/input/GetInput.php
index 1d74d84..1319bf7 100644
--- a/src/schema/input/GetInput.php
+++ b/src/schema/input/GetInput.php
@@ -8,12 +8,12 @@ namespace nur\sery\schema\input;
  * une référence
  */
 class GetInput extends FormInput {
-  function exists($key=null): bool {
+  function isPresent($key=null): bool {
     if ($key === null) return false;
     return array_key_exists($key, $_GET);
   }
 
-  function available($key=null): bool {
+  function isAvailable($key=null): bool {
     if ($key === null) return false;
     if (array_key_exists($key, $_GET)) {
       return $this->allowEmpty || $_GET[$key] !== "";
diff --git a/src/schema/input/Input.php b/src/schema/input/Input.php
index 7f19fff..bbfb540 100644
--- a/src/schema/input/Input.php
+++ b/src/schema/input/Input.php
@@ -24,7 +24,7 @@ class Input {
   protected $dest;
 
   /** tester si la valeur existe sans tenir compte de $allowEmpty */
-  function exits($key=null): bool {
+  function isPresent($key=null): bool {
     if ($key === null) return true;
     $dest = $this->dest;
     return $dest !== null && array_key_exists($key, $dest);
@@ -36,7 +36,7 @@ class Input {
   protected $allowEmpty;
 
   /** tester si la valeur est disponible en tenant compte de $allowEmpty */
-  function available($key=null): bool {
+  function isAvailable($key=null): bool {
     if ($key === null) return true;
     $dest = $this->dest;
     if ($dest === null || !array_key_exists($key, $dest)) return false;
diff --git a/src/schema/input/PostInput.php b/src/schema/input/PostInput.php
index 9cebe08..e76ec8e 100644
--- a/src/schema/input/PostInput.php
+++ b/src/schema/input/PostInput.php
@@ -8,12 +8,12 @@ namespace nur\sery\schema\input;
  * une référence
  */
 class PostInput extends FormInput {
-  function exists($key=null): bool {
+  function isPresent($key=null): bool {
     if ($key === null) return false;
     return array_key_exists($key, $_POST);
   }
 
-  function available($key=null): bool {
+  function isAvailable($key=null): bool {
     if ($key === null) return false;
     if (array_key_exists($key, $_POST)) {
       return $this->allowEmpty || $_POST[$key] !== "";
diff --git a/src/schema/ref/ref_analyze.php b/src/schema/ref/ref_analyze.php
index a640ba1..c95b3e6 100644
--- a/src/schema/ref/ref_analyze.php
+++ b/src/schema/ref/ref_analyze.php
@@ -4,19 +4,21 @@ namespace nur\sery\schema\ref;
 class ref_analyze {
   /** @var int résultat de l'analyse: valeur inexistante */
   const MISSING = 0;
+  /** @var int résultat de l'analyse: valeur non disponible */
+  const UNAVAILABLE = 1;
 
   /** @var int résultat de l'analyse: valeur nulle */
-  const NULL = 1;
+  const NULL = 2;
 
   /** @var int résultat de l'analyse: valeur chaine à parser */
-  const STRING = 2;
+  const STRING = 3;
 
   /** @var int résultat de l'analyse: valeur invalide */
-  const INVALID = 3;
+  const INVALID = 4;
 
   /** @var int résultat de l'analyse: valeur valide mais pas normalisée */
-  const VALID = 4;
+  const VALID = 5;
 
   /** @var int résultat de l'analyse: valeur valide normalisée */
-  const NORMALIZED = 5;
+  const NORMALIZED = 6;
 }
diff --git a/src/schema/ref/ref_schema.php b/src/schema/ref/ref_schema.php
index 3d443ac..e81df51 100644
--- a/src/schema/ref/ref_schema.php
+++ b/src/schema/ref/ref_schema.php
@@ -42,6 +42,7 @@ class ref_schema {
 
   const MESSAGES = [
     "missing" => "{key}: Vous devez spécifier cette valeur",
+    "unavailable" => "{key}: Vous devez spécifier cette valeur",
     "null" => "{key}: Cette valeur ne doit pas être nulle",
     "empty" => "{key}: Cette valeur ne doit pas être vide",
     "invalid" => "{key}: {orig}: cette valeur est invalide",