diff --git a/src/schema/Result.php b/src/schema/Result.php
index 4567c02..6dcfb50 100644
--- a/src/schema/Result.php
+++ b/src/schema/Result.php
@@ -1,30 +1,21 @@
 <?php
 namespace nur\sery\schema;
 
+use nur\sery\schema\_assoc\AssocResult;
+use nur\sery\schema\_list\ListResult;
+use nur\sery\schema\_scalar\ScalarResult;
+
 /**
  * Class Result: résultat de l'analyse ou de la normalisation d'une valeur
- *
- * @property-read bool $valid
- * @property-read string|int|null $key si la valeur est dans un tableau, clé de
- * la valeur dans le tableau
- * @property-read string|null $orig valeur originale avant analyse
- * @property-read string|null $message message d'erreur si la valeur n'est pas
- * valide
  */
-class Result {
-  const KEYS = ["valid", "key", "orig", "message"];
-
-  function __construct(?array $result=null) {
-    if ($result === null) $result = ["valid" => false];
-    foreach (static::KEYS as $key) {
-      if (!array_key_exists($key, $result)) $result[$key] = null;
-    }
-    #XXX interpoler [message] avec les clés de $result
-    $this->result = $result;
+abstract class Result {
+  function __construct() {
+    $this->reset();
   }
 
-  /** @var array  */
-  protected $result;
+  function isAssoc(?AssocResult &$assoc=null): bool { return false; }
+  function isList(?ListResult &$list=null): bool { return false; }
+  function isScalar(?ScalarResult &$scalar=null): bool { return false; }
 
   /**
    * Obtenir la liste des clés valides pour les valeurs accessibles via cet
@@ -35,7 +26,5 @@ class Result {
   /** obtenir un objet pour gérer la valeur spécifiée */
   abstract function getResult($key=null): Result;
 
-  function __get($name) {
-    return $this->result[$name];
-  }
+  abstract function reset(): void;
 }
diff --git a/src/schema/Schema.php b/src/schema/Schema.php
index 22779ca..82b7fa4 100644
--- a/src/schema/Schema.php
+++ b/src/schema/Schema.php
@@ -13,14 +13,14 @@ abstract class Schema implements ArrayAccess {
    * créer si besoin une nouvelle instance de {@link Schema} à partir d'une
    * définition de schéma
    */
-  static function ns(?Schema &$schema, $definition): self {
+  static function ns(?Schema &$schema, $definition, $definitionKey=null): self {
     if ($schema === null) {
       if (AssocSchema::isa_definition($definition)) {
-        $schema = new AssocSchema($definition);
+        $schema = new AssocSchema($definition, $definitionKey);
       } elseif (ListSchema::isa_definition($definition)) {
-        $schema = new ListSchema($definition);
+        $schema = new ListSchema($definition, $definitionKey);
       } elseif (ScalarSchema::isa_definition($definition)) {
-        $schema = new ScalarSchema($definition);
+        $schema = new ScalarSchema($definition, $definitionKey);
       } else {
         throw SchemaException::invalid_schema();
       }
diff --git a/src/schema/SchemaException.php b/src/schema/SchemaException.php
index ac57759..e7988d5 100644
--- a/src/schema/SchemaException.php
+++ b/src/schema/SchemaException.php
@@ -10,15 +10,13 @@ class SchemaException extends Exception {
     return new static($invalid_schema);
   }
 
-  static final function invalid_type($value, ?string $message=null): self {
-    $invalid_type = var_export($value, true).": invalid type";
-    if ($message !== null) $invalid_type .= ": $message";
-    return new static($invalid_type);
+  static final function invalid_kind(string $kind, $value, ?string $message=null): self {
+    $invalid_kind = var_export($value, true).": invalid $kind";
+    if ($message !== null) $invalid_kind .= ": $message";
+    return new static($invalid_kind);
   }
 
-  static final function invalid_callable($value, ?string $message=null): self {
-    $invalid_callable = var_export($value, true).": invalid callable";
-    if ($message !== null) $invalid_callable .= ": $message";
-    return new static($invalid_callable);
+  static final function invalid_type($value, ?string $message=null): self {
+    return self::invalid_kind("type", $value, $message);
   }
 }
diff --git a/src/schema/Value.php b/src/schema/Value.php
index 47feb68..02a8c54 100644
--- a/src/schema/Value.php
+++ b/src/schema/Value.php
@@ -3,9 +3,16 @@ namespace nur\sery\schema;
 
 use ArrayAccess;
 use IteratorAggregate;
+use nur\sery\schema\_assoc\AssocValue;
+use nur\sery\schema\_list\ListValue;
+use nur\sery\schema\_scalar\ScalarValue;
 use nur\sery\schema\types\IType;
 
 abstract class Value implements ArrayAccess, IteratorAggregate {
+  function isAssoc(?AssocValue &$assoc=null): bool { return false; }
+  function isList(?ListValue &$list=null): bool { return false; }
+  function isScalar(?ScalarValue &$scalar=null): bool { return false; }
+
   /** spécifier la valeur destination gérée par cet objet */
   abstract function reset(&$dest, $destKey=null, bool $verifix=true): self;
 
@@ -28,7 +35,7 @@ abstract class Value implements ArrayAccess, IteratorAggregate {
   abstract function getType(): IType;
 
   /** retourner true si la valeur existe */
-  abstract function exists(): bool;
+  abstract function available(): bool;
 
   /** supprimer la valeur */
   abstract function unset(): void;
diff --git a/src/schema/ValueException.php b/src/schema/ValueException.php
new file mode 100644
index 0000000..c210176
--- /dev/null
+++ b/src/schema/ValueException.php
@@ -0,0 +1,20 @@
+<?php
+namespace nur\sery\schema;
+
+use Exception;
+
+class ValueException extends Exception {
+  static final function invalid_kind(string $kind, $value, ?string $message=null): self {
+    $invalid_kind = var_export($value, true).": invalid $kind";
+    if ($message !== null) $invalid_kind .= ": $message";
+    return new static($invalid_kind);
+  }
+
+  static final function invalid_key($value, ?string $message=null): self {
+    return self::invalid_kind("key", $value, $message);
+  }
+
+  static final function invalid_value($value, ?string $message=null): self {
+    return self::invalid_kind("value", $value, $message);
+  }
+}
diff --git a/src/schema/_assoc/AssocResult.php b/src/schema/_assoc/AssocResult.php
index 295813e..7d863db 100644
--- a/src/schema/_assoc/AssocResult.php
+++ b/src/schema/_assoc/AssocResult.php
@@ -4,4 +4,5 @@ namespace nur\sery\schema\_assoc;
 use nur\sery\schema\Result;
 
 class AssocResult extends Result {
+  function isAssoc(?AssocResult &$assoc=null): bool { $assoc = $this; return true;}
 }
diff --git a/src/schema/_assoc/AssocSchema.php b/src/schema/_assoc/AssocSchema.php
index 6673f6c..966d827 100644
--- a/src/schema/_assoc/AssocSchema.php
+++ b/src/schema/_assoc/AssocSchema.php
@@ -31,12 +31,12 @@ class AssocSchema extends Schema {
     return !cl::have_num_keys($definition);
   }
 
-  static function normalize($definition): array {
+  static function normalize($definition, $definitionKey=null): array {
   }
 
-  function __construct($definition=null, bool $normalize=true) {
+  function __construct($definition=null, $definitionKey=null, bool $normalize=true) {
     if ($definition === null) $definition = static::SCHEMA;
-    if ($normalize) $definition = self::normalize($definition);
+    if ($normalize) $definition = self::normalize($definition, $definitionKey);
     $this->definition = $definition;
   }
 
diff --git a/src/schema/_list/ListResult.php b/src/schema/_list/ListResult.php
index 98873df..6ab00d0 100644
--- a/src/schema/_list/ListResult.php
+++ b/src/schema/_list/ListResult.php
@@ -4,4 +4,5 @@ namespace nur\sery\schema\_list;
 use nur\sery\schema\Result;
 
 class ListResult extends Result {
+  function isList(?ListResult &$list=null): bool { $list = $this; return true;}
 }
diff --git a/src/schema/_list/ListSchema.php b/src/schema/_list/ListSchema.php
index 4710724..6f47445 100644
--- a/src/schema/_list/ListSchema.php
+++ b/src/schema/_list/ListSchema.php
@@ -31,12 +31,12 @@ class ListSchema extends Schema {
     return $count == 1 && $haveIndex0 && is_array($definition[0]);
   }
 
-  static function normalize($definition): array {
+  static function normalize($definition, $definitionKey=null): array {
   }
 
-  function __construct($definition=null, bool $normalize=true) {
+  function __construct($definition=null, $definitionKey=null, bool $normalize=true) {
     if ($definition === null) $definition = static::SCHEMA;
-    if ($normalize) $definition = self::normalize($definition);
+    if ($normalize) $definition = self::normalize($definition, $definitionKey);
     $this->definition = $definition;
   }
 
diff --git a/src/schema/_scalar/ScalarResult.php b/src/schema/_scalar/ScalarResult.php
index 533ac04..6e50a29 100644
--- a/src/schema/_scalar/ScalarResult.php
+++ b/src/schema/_scalar/ScalarResult.php
@@ -1,7 +1,82 @@
 <?php
 namespace nur\sery\schema\_scalar;
 
+use nulib\cl;
+use nur\sery\schema\ref\ref_analyze;
 use nur\sery\schema\Result;
+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 $normalized si la valeur est valide, est-elle normalisée?
+ * @property string|null $orig valeur originale avant analyse avec parse()
+ * @property string|null $message message si la valeur n'est pas valide
+ */
 class ScalarResult extends Result {
+  const KEYS = ["missing", "null", "valid", "normalized", "orig", "message"];
+
+  function isScalar(?ScalarResult &$scalar=null): bool { $scalar = $this; return true; }
+
+  function getKeys(): array {
+    return [null];
+  }
+
+  function getResult($key=null): Result {
+    if ($key === null) return $this;
+    else throw ValueException::invalid_key($key);
+  }
+
+  /** @var array  */
+  protected $result;
+  
+  function reset(): void {
+    $this->result = array_merge(
+      array_fill_keys(static::KEYS, null), [
+      "missing" => true,
+      "null" => false,
+      "valid" => false,
+      "normalized" => false,
+    ]);
+  }
+
+  function __get(string $name) {
+    return $this->result[$name];
+  }
+
+  function __set(string $name, $value): void {
+    $this->result[$name] = $value;
+  }
+
+  function setMissing(ScalarSchema $schema, ?string $key=null): int {
+    $this->missing = true;
+    if (!$schema->required) {
+      $this->null = true;
+      $this->valid = true;
+      $this->normalized = true;
+      return ref_analyze::NORMALIZED;
+    } else {
+      $message = cl::get($schema->messages, "missing");
+      $message = str_replace("{key}", $key, $message);
+      $this->message = $message;
+      return ref_analyze::MISSING;
+    }
+  }
+
+  function setNull(ScalarSchema $schema, ?string $key=null): int {
+    $this->missing = true;
+    if ($schema->nullable) {
+      $this->valid = true;
+      $this->normalized = true;
+      return ref_analyze::NORMALIZED;
+    } else {
+      $message = cl::get($schema->messages, "null");
+      $message = str_replace("{key}", $key, $message);
+      $this->message = $message;
+      return ref_analyze::NULL;
+    }
+  }
 }
diff --git a/src/schema/_scalar/ScalarSchema.php b/src/schema/_scalar/ScalarSchema.php
index 8f07377..42b3f5d 100644
--- a/src/schema/_scalar/ScalarSchema.php
+++ b/src/schema/_scalar/ScalarSchema.php
@@ -169,9 +169,9 @@ class ScalarSchema extends Schema {
     return $definition;
   }
 
-  function __construct($definition=null, bool $normalize=true) {
+  function __construct($definition=null, $definitionKey=null, bool $normalize=true) {
     if ($definition === null) $definition = static::SCHEMA;
-    if ($normalize) $definition = self::normalize($definition);
+    if ($normalize) $definition = self::normalize($definition, $definitionKey);
     $this->definition = $definition;
   }
 
diff --git a/src/schema/_scalar/ScalarValue.php b/src/schema/_scalar/ScalarValue.php
index 74564c7..b69b64e 100644
--- a/src/schema/_scalar/ScalarValue.php
+++ b/src/schema/_scalar/ScalarValue.php
@@ -2,13 +2,16 @@
 namespace nur\sery\schema\_scalar;
 
 use nur\sery\schema\input\Input;
+use nur\sery\schema\ref\ref_analyze;
 use nur\sery\schema\Result;
 use nur\sery\schema\types\IType;
 use nur\sery\schema\Value;
+use nur\sery\schema\ValueException;
 
 class ScalarValue extends Value {
   function __construct(ScalarSchema $schema, &$dest=null, $key=null, bool $verifix=true) {
     $this->schema = $schema;
+    $this->result = new ScalarResult();
     $this->reset($dest, $key, $verifix);
   }
 
@@ -23,7 +26,10 @@ class ScalarValue extends Value {
   /** @var string|int clé de la valeur dans le tableau destination */
   protected $destKey;
 
-  /** @var ?Result résultat de l'analyse de la valeur */
+  /** @var IType */
+  protected $type;
+
+  /** @var ?ScalarResult résultat de l'analyse de la valeur */
   protected $result;
 
   function reset(&$dest, $destKey=null, bool $verifix=true): Value {
@@ -34,28 +40,53 @@ class ScalarValue extends Value {
     $this->result = null;
     #XXX résoudre les types ici?
     if ($verifix) $this->verifix();
+    else $this->_analyze();
     return $this;
   }
 
+  function getKeys(): array {
+    return [null];
+  }
+
+  function getValue($key=null): Value {
+    if ($key === null) return $this;
+    throw ValueException::invalid_key($key);
+  }
+
+  /** analyser la valeur et résoudre son type */
+  function _analyze(): int {
+    $schema = $this->schema;
+    $input = $this->input;
+    $destKey = $this->destKey;
+    $result = $this->result;
+    $result->reset();
+    if (!$input->available()) return $result->setMissing($schema, $destKey);
+    $value = $input->get($destKey);
+    if ($value === null) return $result->setNull($schema, $destKey);
+    #XXX résoudre le type
+  }
+
   function exists(): bool {
-    return $this->input->exists($this->destKey);
+    return $this->input->exits($this->destKey);
+  }
+
+  function available(): bool {
+    return $this->input->available($this->destKey);
   }
 
   function get($default=null) {
     $destKey = $this->destKey;
     $input = $this->input;
-    if ($input->exists($destKey)) return $input->get($destKey);
+    if ($input->available($destKey)) return $input->get($destKey);
     else return $default;
   }
 
-  function set($value): self {
+  function set($value, bool $verifix=true): Value {
     $this->input->set($value, $this->destKey);
+    if ($verifix) $this->verifix();
     return $this;
   }
 
-  /** @var IType */
-  protected $type;
-
   function getType(): IType {
     if ($this->type === null) $this->type = $this->schema->getType($this->destKey);
     return $this->type;
diff --git a/src/schema/input/FormInput.php b/src/schema/input/FormInput.php
index 5a48b4d..fcd0b22 100644
--- a/src/schema/input/FormInput.php
+++ b/src/schema/input/FormInput.php
@@ -12,15 +12,36 @@ namespace nur\sery\schema\input;
  *
  */
 class FormInput extends Input {
+  const ALLOW_EMPTY = false;
+
   function exists($key=null): bool {
     if ($key === null) return false;
     return array_key_exists($key, $_POST) || array_key_exists($key, $_GET);
   }
 
+  function available($key=null): bool {
+    if ($key === null) return false;
+    if (array_key_exists($key, $_POST)) {
+      return $this->allowEmpty || $_POST[$key] !== "";
+    } elseif (array_key_exists($key, $_GET)) {
+      return $this->allowEmpty || $_GET[$key] !== "";
+    } else {
+      return false;
+    }
+  }
+
   function get($key=null) {
     if ($key === null) return null;
-    if (array_key_exists($key, $_POST)) return $_POST[$key];
-    elseif (array_key_exists($key, $_GET)) return $_GET[$key];
-    else return null;
+    if (array_key_exists($key, $_POST)) {
+      $value = $_POST[$key];
+      if ($value === "" && !$this->allowEmpty) return null;
+      return $value;
+    } elseif (array_key_exists($key, $_GET)) {
+      $value = $_GET[$key];
+      if ($value === "" && !$this->allowEmpty) return null;
+      return $value;
+    } else {
+      return null;
+    }
   }
 }
diff --git a/src/schema/input/GetInput.php b/src/schema/input/GetInput.php
index aa0c8c4..1d74d84 100644
--- a/src/schema/input/GetInput.php
+++ b/src/schema/input/GetInput.php
@@ -13,9 +13,23 @@ class GetInput extends FormInput {
     return array_key_exists($key, $_GET);
   }
 
+  function available($key=null): bool {
+    if ($key === null) return false;
+    if (array_key_exists($key, $_GET)) {
+      return $this->allowEmpty || $_GET[$key] !== "";
+    } else {
+      return false;
+    }
+  }
+
   function get($key=null) {
     if ($key === null) return null;
-    if (array_key_exists($key, $_GET)) return $_GET[$key];
-    else return null;
+    if (array_key_exists($key, $_GET)) {
+      $value = $_GET[$key];
+      if ($value === "" && !$this->allowEmpty) return null;
+      return $value;
+    } else {
+      return null;
+    }
   }
 }
diff --git a/src/schema/input/Input.php b/src/schema/input/Input.php
index 3a6c7b6..7f19fff 100644
--- a/src/schema/input/Input.php
+++ b/src/schema/input/Input.php
@@ -4,29 +4,52 @@ namespace nur\sery\schema\input;
 #XXX available permet de préciser qu'une valeur doit exister et être non vide
 # pour être considérée. en faire un paramètre, à moins que ce soit au niveau du
 # type qu'il faille le gérer?
+use nulib\cl;
+
 /**
  * Class Input: accès à une valeur
  *
  * cette implémentation lit depuis et écrit dans une référence
  */
 class Input {
-  function __construct(&$dest=null) {
+  const ALLOW_EMPTY = true;
+
+  function __construct(&$dest=null, ?array $params=null) {
     $this->dest =& $dest;
+    $allowEmpty = cl::get($params, "allow_empty");
+    if ($allowEmpty === null) $allowEmpty = static::ALLOW_EMPTY;
+    $this->allowEmpty = $allowEmpty;
   }
 
   protected $dest;
 
-  /** tester si la valeur existe */
-  function exists($key=null): bool {
+  /** tester si la valeur existe sans tenir compte de $allowEmpty */
+  function exits($key=null): bool {
     if ($key === null) return true;
-    return $this->dest !== null && array_key_exists($key, $this->dest);
+    $dest = $this->dest;
+    return $dest !== null && array_key_exists($key, $dest);
+  }
+
+  /**
+   * @var bool comment considérer une chaine vide: "" si allowEmpty, null sinon
+   */
+  protected $allowEmpty;
+
+  /** tester si la valeur est disponible en tenant compte de $allowEmpty */
+  function available($key=null): bool {
+    if ($key === null) return true;
+    $dest = $this->dest;
+    if ($dest === null || !array_key_exists($key, $dest)) return false;
+    return $this->allowEmpty || $dest[$key] !== "";
   }
 
   function get($key=null) {
-    if ($key === null) return $this->dest;
-    elseif ($this->dest === null) return null;
-    elseif (!array_key_exists($key, $this->dest)) return null;
-    else return $this->dest[$key];
+    $dest = $this->dest;
+    if ($key === null) return $dest;
+    if ($dest === null || !array_key_exists($key, $dest)) return null;
+    $value = $dest[$key];
+    if ($value === "" && !$this->allowEmpty) return null;
+    return $value;
   }
 
   function set($value, $key=null): void {
diff --git a/src/schema/input/PostInput.php b/src/schema/input/PostInput.php
index 80f2b22..9cebe08 100644
--- a/src/schema/input/PostInput.php
+++ b/src/schema/input/PostInput.php
@@ -13,9 +13,23 @@ class PostInput extends FormInput {
     return array_key_exists($key, $_POST);
   }
 
+  function available($key=null): bool {
+    if ($key === null) return false;
+    if (array_key_exists($key, $_POST)) {
+      return $this->allowEmpty || $_POST[$key] !== "";
+    } else {
+      return false;
+    }
+  }
+
   function get($key=null) {
     if ($key === null) return null;
-    if (array_key_exists($key, $_POST)) return $_POST[$key];
-    else return null;
+    if (array_key_exists($key, $_POST)) {
+      $value = $_POST[$key];
+      if ($value === "" && !$this->allowEmpty) return null;
+      return $value;
+    } else {
+      return null;
+    }
   }
 }
diff --git a/src/schema/ref/ref_schema.php b/src/schema/ref/ref_schema.php
index 3d7f2de..3d443ac 100644
--- a/src/schema/ref/ref_schema.php
+++ b/src/schema/ref/ref_schema.php
@@ -41,7 +41,7 @@ class ref_schema {
   ];
 
   const MESSAGES = [
-    "absent" => "{key}: Vous devez spécifier cette valeur",
+    "missing" => "{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",
diff --git a/src/schema/types/tcallable.php b/src/schema/types/tcallable.php
index 54d83a4..6293b5a 100644
--- a/src/schema/types/tcallable.php
+++ b/src/schema/types/tcallable.php
@@ -1,11 +1,11 @@
 <?php
 namespace nur\sery\schema\types;
 
-use nur\sery\schema\SchemaException;
+use nur\sery\schema\ValueException;
 
 class tcallable implements IType {
   static function ensure_callable(&$callable): void {
-    if (!is_callable($callable)) throw SchemaException::invalid_callable($callable);
+    if (!is_callable($callable)) throw ValueException::invalid_value($callable);
   }
 
   static function ensure_ncallable(&$callable): void {