diff --git a/src/Composer/Downloader/DownloaderInterface.php b/src/Composer/Downloader/DownloaderInterface.php
index 4416ac46e..7a114ea2b 100644
--- a/src/Composer/Downloader/DownloaderInterface.php
+++ b/src/Composer/Downloader/DownloaderInterface.php
@@ -15,10 +15,36 @@ namespace Composer\Downloader;
 use Composer\Package\PackageInterface;
 
 /**
+ * Downloader interface.
+ *
  * @author Konstantin Kudryashov <ever.zet@gmail.com>
  */
 interface DownloaderInterface
 {
+    /**
+     * Downloads specific package into specific folder.
+     *
+     * @param   PackageInterface    $package    package instance
+     * @param   string              $path       download path
+     * @param   string              $url        download url
+     * @param   string              $checksum   package checksum (for dists)
+     */
     function download(PackageInterface $package, $path, $url, $checksum = null);
-    function isDownloaded(PackageInterface $package, $path);
+
+    /**
+     * Updates specific package in specific folder from initial to target version.
+     *
+     * @param   PackageInterface    $initial    initial package
+     * @param   PackageInterface    $target     updated package
+     * @param   string              $path       download path
+     */
+    function update(PackageInterface $initial, PackageInterface $target, $path);
+
+    /**
+     * Removes specific package from specific folder.
+     *
+     * @param   PackageInterface    $package    package instance
+     * @param   string              $path       download path
+     */
+    function remove(PackageInterface $package, $path);
 }