diff --git a/src/php/time/Time.php b/src/php/time/Time.php
index 115c152..dae044f 100644
--- a/src/php/time/Time.php
+++ b/src/php/time/Time.php
@@ -31,8 +31,13 @@ class Time {
     else return new static($time);
   }
 
-  static function ensure(&$time): void {
-    $time = static::withn($time);
+  static function isa_time($time): bool {
+    if ($time === null) return false;
+    if ($time instanceof Time) return true;
+    if (is_int($time)) return true;
+    if (is_string($time)) return preg_match(self::PATTERN, $time);
+    #XXX supporter tous les formats
+    return false;
   }
 
   static function seconds_now(): int {
diff --git a/src/php/types/vdate.php b/src/php/types/vdate.php
index 85b1d43..3f102f7 100644
--- a/src/php/types/vdate.php
+++ b/src/php/types/vdate.php
@@ -4,6 +4,11 @@ namespace nulib\php\types;
 use nulib\php\time\Date;
 
 class vdate {
+  static function isa($value, bool $strict=false) : bool {
+    if ($strict) return $value instanceof Date;
+    else return Date::isa_date($value);
+  }
+
   static function ensure(&$date): void {
     $date = Date::with($date);
   }
diff --git a/src/php/types/vdatetime.php b/src/php/types/vdatetime.php
index 2f0ecc0..7304438 100644
--- a/src/php/types/vdatetime.php
+++ b/src/php/types/vdatetime.php
@@ -4,6 +4,11 @@ namespace nulib\php\types;
 use nulib\php\time\DateTime;
 
 class vdatetime {
+  static function isa($value, bool $strict=false) : bool {
+    if ($strict) return $value instanceof DateTime;
+    else return DateTime::isa_datetime($value);
+  }
+
   static function ensure(&$datetime): void {
     $datetime = DateTime::with($datetime);
   }
diff --git a/src/php/types/vmixed.php b/src/php/types/vmixed.php
index 71630f8..ec02597 100644
--- a/src/php/types/vmixed.php
+++ b/src/php/types/vmixed.php
@@ -2,6 +2,10 @@
 namespace nulib\php\types;
 
 class vmixed {
+  static function isa($value, bool $strict=false) : bool {
+    return true;
+  }
+
   static function ensure(&$mixed): void {
   }
 
diff --git a/src/php/types/vraw.php b/src/php/types/vraw.php
index a63d4c1..ef3ee0a 100644
--- a/src/php/types/vraw.php
+++ b/src/php/types/vraw.php
@@ -2,6 +2,10 @@
 namespace nulib\php\types;
 
 class vraw {
+  static function isa($value, bool $strict=false) : bool {
+    return true;
+  }
+
   static function ensure(&$raw): void {
   }
 
diff --git a/src/php/types/vschema.php b/src/php/types/vschema.php
index 9d5c024..c32a25a 100644
--- a/src/php/types/vschema.php
+++ b/src/php/types/vschema.php
@@ -1,6 +1,9 @@
 <?php
 namespace nulib\php\types;
 
+use nulib\exceptions;
+use nulib\str;
+
 /**
  * Class vschema: gestionsimplifiée de schémas associatifs
  *
@@ -8,7 +11,7 @@ namespace nulib\php\types;
  */
 class vschema {
   /** @var array types valides */
-  const TYPES = [
+  const VCLASSES = [
     "rawstring" => vrawstring::class,
     "string" => vstring::class,
     "text" => vtext::class,
@@ -27,9 +30,62 @@ class vschema {
     "time" => vtime::class,
   ];
 
-  /** indiquer si $value est conforme au schéma */
-  static function check($value, array $schema): bool {
+  private static function get_types($schema): array {
+    if (is_array($schema)) {
+      $types = $schema["type"] ?? $schema[0] ?? null;
+    } elseif (is_string($schema)) {
+      $types = $schema;
+    } else {
+      throw exceptions::invalid_value($schema, "schema");
+    }
+    if (is_string($types)) {
+      $types = explode(",", $types);
+    } elseif (!is_array($types)) {
+      throw exceptions::invalid_value($types, "types");
+    }
+    return $types;
+  }
 
+  private static function get_vclass(array $types, ?bool &$nullable): ?string {
+    foreach ($types as $type) {
+      $vclass = self::VCLASSES[$type] ?? null;
+      if ($vclass !== null) {
+        $nullable = str::del_prefix($type, "?");
+        return $vclass;
+      }
+    }
+    return null;
+  }
+
+  /** indiquer si $value est conforme au schéma */
+  static function check_scalar($value, $schema, bool $strict=false): bool {
+    $types = self::get_types($schema);
+    $vclass = self::get_vclass($types, $nullable);
+    # ce doit être un type supporté
+    if ($vclass === null) return false;
+    if ($value === null) return $nullable;
+    return $vclass::isa($value, $strict);
+  }
+
+  static function ensure_scalar(&$value, $schema): bool {
+    $types = self::get_types($schema);
+    $vclass = self::get_vclass($types, $nullable);
+    # ce doit être un type supporté
+    if ($vclass === null) return false;
+    if ($nullable) $value = $vclass::withn($value);
+    else $value = $vclass::with($value);
+    return true;
+  }
+
+  /** indiquer si $value est conforme au schéma */
+  static function check_assoc(?array $array, array $schema): bool {
+    foreach ($schema as $key => $kschema) {
+      $required = vbool::with($kschema["required"] ?? false);
+      $exists = array_key_exists($key, $array);
+      if (!$exists && $required) return false;
+      if (!self::check_scalar($array[$key], $kschema)) return false;
+    }
+    return true;
   }
 
   /**
@@ -37,7 +93,7 @@ class vschema {
    * - les clés ne sont pas créées si elles n'existent pas
    *
    */
-  static function ensure(&$value, array $schema): void {
+  static function ensure_assoc(&$value, array $schema): void {
 
   }
 }
diff --git a/src/php/types/vtime.php b/src/php/types/vtime.php
index 1c0f9c6..a96dbe8 100644
--- a/src/php/types/vtime.php
+++ b/src/php/types/vtime.php
@@ -1,9 +1,15 @@
 <?php
 namespace nulib\php\types;
 
+use nulib\php\time\DateTime;
 use nulib\php\time\Time;
 
 class vtime {
+  static function isa($value, bool $strict=false) : bool {
+    if ($strict) return $value instanceof Time;
+    else return Time::isa_time($value);
+  }
+
   static function ensure(&$time): void {
     $time = Time::with($time);
   }