diff --git "a/include/class-wb\\DataValue.php" "b/include/class-wb\\DataValue.php"
index 8d03f08..e976f89 100644
--- "a/include/class-wb\\DataValue.php"
+++ "b/include/class-wb\\DataValue.php"
@@ -1,98 +1,121 @@
 <?php
 # Boz-MW - Another MediaWiki API handler in PHP
 # Copyright (C) 2017, 2018, 2019 Valerio Bozzolan
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU Affero General Public License as published by
 # the Free Software Foundation, either version 3 of the License, or
 # (at your option) any later version.
 #
 # This program is distributed in the hope that it will be useful,
 # but WITHOUT ANY WARRANTY; without even the implied warranty of
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 # GNU Affero General Public License for more details.
 #
 # You should have received a copy of the GNU General Public License
 # along with this program. If not, see <http://www.gnu.org/licenses/>.
 
 # Wikibase
 namespace wb;
 
 /**
- * A generic DataValue is part of a Snak.
+ * A generic DataValue is part of a Snak
  */
 class DataValue {
 
-	var $type;
-	var $value;
+	/**
+	 * Type of the DataValue
+	 *
+	 * @var string
+	 */
+	private $type;
+
+	/**
+	 * Value of the DataValue
+	 *
+	 * @var array
+	 */
+	private $value;
 
 	/**
 	 * Constructor
 	 *
 	 * @param $type  string Type
 	 * @param $value mixed  Value
 	 */
 	public function __construct( $type, $value ) {
 		$this->setType(  $type )
 		     ->setValue( $value );
 	}
 
 	/**
 	 * Get the type
 	 *
 	 * @return string
 	 */
 	public function getType() {
 		return $this->type;
 	}
 
 	/**
 	 * Get the value
 	 *
 	 * @return mixed
 	 */
 	public function getValue() {
 		return $this->value;
 	}
 
 	/**
 	 * Set the type
 	 */
 	public function setType( $type ) {
 		$this->type = $type;
 		return $this;
 	}
 
 	/**
 	 * Set the value
 	 *
 	 * @param  mixed $value
 	 * @return self
 	 */
 	public function setValue( $value ) {
 		$this->value = $value;
 		return $this;
 	}
 
 	/**
 	 * Static constructor from a standard object
 	 *
 	 * @param  object $data
 	 * @return self
 	 */
 	public static function createFromData( $data ) {
 		if( ! isset( $data['type'], $data['value'] ) ) {
 			throw new WrongDataException( __CLASS__ );
 		}
 		return new self( $data['type'], $data['value'] );
 	}
 
+	/**
+	 * Export this object to an associative array suitable for JSON-encoding
+	 *
+	 * @return array
+	 */
+	public function toData() {
+		return [
+			'type'  => $this->getType(),
+			'value' => $this->getValue(),
+		];
+	}
+
 	/**
 	 * Get this object in form of a string
 	 *
 	 * @return string
 	 */
 	public function __toString() {
 		return json_encode( $this->getValue() );
 	}
 }
diff --git "a/include/class-wb\\Snak.php" "b/include/class-wb\\Snak.php"
index 9f76f6f..825e481 100644
--- "a/include/class-wb\\Snak.php"
+++ "b/include/class-wb\\Snak.php"
@@ -1,245 +1,249 @@
 <?php
 # Boz-MW - Another MediaWiki API handler in PHP
 # Copyright (C) 2017, 2018, 2019 Valerio Bozzolan
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU Affero General Public License as published by
 # the Free Software Foundation, either version 3 of the License, or
 # (at your option) any later version.
 #
 # This program is distributed in the hope that it will be useful,
 # but WITHOUT ANY WARRANTY; without even the implied warranty of
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 # GNU Affero General Public License for more details.
 #
 # You should have received a copy of the GNU General Public License
 # along with this program. If not, see <http://www.gnu.org/licenses/>.
 
 # Wikibase
 namespace wb;
 
 /**
  * A generic Snak is a combination of a property and a datatype + datavalue.
  *
  * A Snak is part of a Claim or a Reference. It's based on a DataValue.
  */
 class Snak {
 
 	private $hash;
 
 	private $snaktype;
 
 	private $property;
 
 	private $datatype;
 
 	private $datavalue;
 
 	/**
 	 * @param $snaktype string
 	 * @param $property string
 	 * @param $datatype string
 	 * @param $datavalue mixed
 	 */
 	public function __construct( $snaktype, $property, $datatype, $datavalue = null ) {
 		$this->setSnakType(  $snaktype )
 		     ->setProperty(  $property )
 		     ->setDataType(  $datatype );
 
 		if( null !== $datavalue ) {
 			 $this->setDataValue( $datavalue );
 		}
 	}
 
 	/**
 	 * Get the property
 	 *
 	 * @return string
 	 */
 	public function getProperty() {
 		return $this->property;
 	}
 
 	/**
 	 * Get the snak type
 	 */
 	public function getSnakType() {
 		return $this->snaktype;
 	}
 
 	/**
 	 * Get the data type
 	 */
 	public function getDataType() {
 		return $this->datatype;
 	}
 
 	/**
 	 * Get the data value
 	 *
 	 * @return DataValue
 	 */
 	public function getDataValue() {
 		return $this->datavalue;
 	}
 
 	/**
 	 * Set the snak type
 	 *
 	 * @param $snaktype
 	 * @param self
 	 */
 	public function setSnakType( $snaktype ) {
 		$this->snaktype = $snaktype;
 		return $this;
 	}
 
 	/**
 	 * Set the property
 	 *
 	 * @param $property string
 	 * @param self
 	 */
 	public function setProperty( $property ) {
 		$this->property = $property;
 		return $this;
 	}
 
 	/**
 	 * Get an human property label, if available in cache
 	 */
 	public function getPropertyLabel() {
 		return self::propertyLabel( $this->getProperty() );
 	}
 
 	/**
 	 * Set the data type
 	 *
 	 * @param $datatype
 	 * @param self
 	 */
 	public function setDataType( $datatype ) {
 		$this->datatype = $datatype;
 		return $this;
 	}
 
 	/**
 	 * Set the data value
 	 *
 	 * @param $datavalue DataValue
 	 * @param self
 	 */
 	public function setDataValue( DataValue $datavalue ) {
 		$this->datavalue = $datavalue;
 		return $this;
 	}
 
 	/**
 	 * Check if the snak has an hash
 	 *
 	 * @return bool
 	 */
 	public function hasHash() {
 		return isset( $this->hash );
 	}
 
 	/**
 	 * Get the hash
 	 *
 	 * @return string|null
 	 */
 	public function getHash() {
 		return $this->hash;
 	}
 
 	/**
 	 * Set the hash
 	 *
 	 * @param $hash string
 	 * @return self
 	 */
 	public function setHash( $hash ) {
 		$this->hash = $hash;
 		return $this;
 	}
 
 	/**
 	 * Get a wikilink to this property
 	 *
 	 * @return string
 	 */
 	protected function getPropertyWLink() {
 		$prop  = $this->getProperty();
 		$label = $this->getPropertyLabel();
 		if( ! $label ) {
 			$label = $prop;
 		}
 		return sprintf( '[[P:%s|%s]]', $prop, $label );
 	}
 
 	/**
 	 * Try to read the property label from the cache
 	 *
 	 * @TODO: ask also the site
 	 * @return string|false
 	 */
 	public static function propertyLabel( $property ) {
 		return \wm\Wikidata::propertyLabel( $property );
 	}
 
 	/**
 	 * Create a snak from raw data
 	 *
 	 * @param $data array
 	 * @return self
 	 */
 	public static function createFromData( $data ) {
 		if( ! isset( $data['snaktype'], $data['property'], $data['datatype'] ) ) {
 			var_dump( $data );
 			throw new WrongDataException( __CLASS__ );
 		}
 		$snak = new self(
 			$data['snaktype'],
 			$data['property'],
 			$data['datatype']
 		);
 		if( isset( $data['datavalue'] ) ) {
 			$snak->setDataValue( DataValue::createFromData( $data['datavalue'] ) );
 		}
 		if( isset( $data['hash'] ) ) {
 			$snak->setHash( $data['hash'] );
 		}
 		return $snak;
 	}
 
 	/**
 	 * Convert this object to an associative array suitable for JSON encoding
 	 *
 	 * @return array
 	 */
 	public function toData() {
 		$data = [];
 
 		// it may have an hash
 		if( $this->hasHash() ) {
 			$data['hash'] = $this->getHash();
 		}
 
 		$data['snaktype']  = $this->getSnakType();
 		$data['property']  = $this->getProperty();
 		$data['datatype']  = $this->getDataType();
 		$data['datavalue'] = $this->getDataValue();
 
+		if( $data['datavalue'] ) {
+			$data['datavalue'] = $data['datavalue']->toData();
+		}
+
 		return $data;
 	}
 
 	/**
 	 * @return string
 	 */
 	public function __toString() {
 		return sprintf( '%s: %s',
 			$this->getPropertyWLink(),
 			$this->getDataValue()
 		);
 	}
 }