diff --git a/core/modules/book/book.services.yml b/core/modules/book/book.services.yml
index f84ead9..ce5f3cd 100644
--- a/core/modules/book/book.services.yml
+++ b/core/modules/book/book.services.yml
@@ -6,7 +6,7 @@ services:
       - { name: breadcrumb_builder, priority: 701 }
   book.manager:
     class: Drupal\book\BookManager
-    arguments: ['@entity.manager', '@string_translation', '@config.factory', '@book.storage']
+    arguments: ['@entity.manager', '@string_translation', '@config.factory', '@book.outline_storage']
     tags:
       - { name: backend_overridable }
   book.outline:
@@ -15,7 +15,7 @@ services:
   book.export:
     class: Drupal\book\BookExport
     arguments: ['@entity.manager', '@book.manager']
-  book.storage:
+  book.outline_storage:
     class: Drupal\book\BookOutlineStorage
     arguments: ['@database']
   access_check.book.removable:
diff --git a/core/modules/book/src/BookManager.php b/core/modules/book/src/BookManager.php
index 42ee817..0035cd3 100644
--- a/core/modules/book/src/BookManager.php
+++ b/core/modules/book/src/BookManager.php
@@ -50,11 +50,11 @@ class BookManager implements BookManagerInterface {
   protected $books;
 
   /**
-   * Book Storage.
+   * Book outline storage.
    *
    * @var \Drupal\book\BookOutlineStorageInterface
    */
-  protected $bookStorage;
+  protected $bookOutlineStorage;
 
   /**
    * Stores flattened book trees.
@@ -66,11 +66,11 @@ class BookManager implements BookManagerInterface {
   /**
    * Constructs a BookManager object.
    */
-  public function __construct(EntityManagerInterface $entity_manager, TranslationInterface $translation, ConfigFactoryInterface $config_factory, BookOutlineStorageInterface $book_storage) {
+  public function __construct(EntityManagerInterface $entity_manager, TranslationInterface $translation, ConfigFactoryInterface $config_factory, BookOutlineStorageInterface $book_outline_storage) {
     $this->entityManager = $entity_manager;
     $this->stringTranslation = $translation;
     $this->configFactory = $config_factory;
-    $this->bookStorage = $book_storage;
+    $this->bookOutlineStorage = $book_outline_storage;
   }
 
   /**
@@ -88,10 +88,10 @@ public function getAllBooks() {
    */
   protected function loadBooks() {
     $this->books = array();
-    $nids = $this->bookStorage->getBooks();
+    $nids = $this->bookOutlineStorage->getBooks();
 
     if ($nids) {
-      $book_links = $this->bookStorage->loadMultiple($nids);
+      $book_links = $this->bookOutlineStorage->loadMultiple($nids);
       $nodes = $this->entityManager->getStorage('node')->loadMultiple($nids);
       // @todo: Sort by weight and translated title.
 
@@ -141,7 +141,7 @@ public function getParentDepthLimit(array $book_link) {
    *   the passed book link.
    */
   protected function findChildrenRelativeDepth(array $book_link) {
-    $max_depth = $this->bookStorage->getChildRelativeDepth($book_link, static::BOOK_MAX_DEPTH);
+    $max_depth = $this->bookOutlineStorage->getChildRelativeDepth($book_link, static::BOOK_MAX_DEPTH);
     return ($max_depth > $book_link['depth']) ? $max_depth - $book_link['depth'] : 0;
   }
 
@@ -415,11 +415,11 @@ public function getTableOfContents($bid, $depth_limit, array $exclude = array())
    */
   public function deleteFromBook($nid) {
     $original = $this->loadBookLink($nid, FALSE);
-    $this->bookStorage->delete($nid);
+    $this->bookOutlineStorage->delete($nid);
 
     if ($nid == $original['bid']) {
       // Handle deletion of a top-level post.
-      $result = $this->bookStorage->loadBookChildren($nid);
+      $result = $this->bookOutlineStorage->loadBookChildren($nid);
 
       foreach ($result as $child) {
         $child['bid'] = $child['nid'];
@@ -608,7 +608,7 @@ protected function doBookTreeBuild($bid, array $parameters = array()) {
 
     if (!isset($trees[$tree_cid])) {
       $min_depth = (isset($parameters['min_depth']) ? $parameters['min_depth'] : 1);
-      $result = $this->bookStorage->getBookMenuTree($bid, $parameters, $min_depth, static::BOOK_MAX_DEPTH);
+      $result = $this->bookOutlineStorage->getBookMenuTree($bid, $parameters, $min_depth, static::BOOK_MAX_DEPTH);
 
       // Build an ordered array of links using the query result object.
       $links = array();
@@ -690,7 +690,7 @@ public function loadBookLink($nid, $translate = TRUE) {
    * {@inheritdoc}
    */
   public function loadBookLinks($nids, $translate = TRUE) {
-    $result = $this->bookStorage->loadMultiple($nids);
+    $result = $this->bookOutlineStorage->loadMultiple($nids);
     $links = array();
     foreach ($result as $link) {
       if ($translate) {
@@ -712,7 +712,7 @@ public function saveBookLink(array $link, $new) {
     if ($new) {
       // Insert new.
       $parents = $this->getBookParents($link, (array) $this->loadBookLink($link['pid'], FALSE));
-      $this->bookStorage->insert($link, $parents);
+      $this->bookOutlineStorage->insert($link, $parents);
 
       // Update the has_children status of the parent.
       $this->updateParent($link);
@@ -748,7 +748,7 @@ public function saveBookLink(array $link, $new) {
         $this->updateParent($link);
       }
       // Update the weight and pid.
-      $this->bookStorage->update($link['nid'], array(
+      $this->bookOutlineStorage->update($link['nid'], array(
         'weight' => $link['weight'],
         'pid' => $link['pid'],
         'bid' => $link['bid'],
@@ -791,7 +791,7 @@ protected function moveChildren(array $link, array $original) {
       $expressions = array_reverse($expressions);
     }
 
-    $this->bookStorage->updateMovedChildren($link['bid'], $original, $expressions, $shift);
+    $this->bookOutlineStorage->updateMovedChildren($link['bid'], $original, $expressions, $shift);
   }
 
   /**
@@ -813,7 +813,7 @@ protected function updateParent(array $link) {
       // Nothing to update.
       return TRUE;
     }
-    return $this->bookStorage->update($link['pid'], array('has_children' => 1));
+    return $this->bookOutlineStorage->update($link['pid'], array('has_children' => 1));
   }
 
   /**
@@ -836,13 +836,13 @@ protected function updateOriginalParent(array $original) {
       return TRUE;
     }
     // Check if $original had at least one child.
-    $original_number_of_children = $this->bookStorage->countOriginalLinkChildren($original);
+    $original_number_of_children = $this->bookOutlineStorage->countOriginalLinkChildren($original);
 
     $parent_has_children = ((bool) $original_number_of_children) ? 1 : 0;
     // Update the parent. If the original link did not have children, then the
     // parent now does not have children. If the original had children, then the
     // the parent has children now (still).
-    return $this->bookStorage->update($original['pid'], array('has_children' => $parent_has_children));
+    return $this->bookOutlineStorage->update($original['pid'], array('has_children' => $parent_has_children));
   }
 
   /**
@@ -1028,7 +1028,7 @@ public function bookSubtreeData($link) {
 
       // If the subtree data was not in the cache, $data will be NULL.
       if (!isset($data)) {
-        $result = $this->bookStorage->getBookSubtree($link, static::BOOK_MAX_DEPTH);
+        $result = $this->bookOutlineStorage->getBookSubtree($link, static::BOOK_MAX_DEPTH);
         $links = array();
         foreach ($result as $item) {
           $links[] = $item;
diff --git a/core/modules/book/tests/src/Unit/BookManagerTest.php b/core/modules/book/tests/src/Unit/BookManagerTest.php
index e74d8ae..2c12385 100644
--- a/core/modules/book/tests/src/Unit/BookManagerTest.php
+++ b/core/modules/book/tests/src/Unit/BookManagerTest.php
@@ -45,11 +45,11 @@ class BookManagerTest extends UnitTestCase {
   protected $bookManager;
 
   /**
-   * Book Storage.
+   * Book outline storage.
    *
    * @var \Drupal\book\BookOutlineStorageInterface
    */
-  protected $bookStorage;
+  protected $bookOutlineStorage;
 
   /**
    * {@inheritdoc}
@@ -58,8 +58,8 @@ protected function setUp() {
     $this->entityManager = $this->getMock('Drupal\Core\Entity\EntityManagerInterface');
     $this->translation = $this->getStringTranslationStub();
     $this->configFactory = $this->getConfigFactoryStub(array());
-    $this->bookStorage = $this->getMock('Drupal\book\BookOutlineStorageInterface');
-    $this->bookManager = new BookManager($this->entityManager, $this->translation, $this->configFactory, $this->bookStorage);
+    $this->bookOutlineStorage = $this->getMock('Drupal\book\BookOutlineStorageInterface');
+    $this->bookManager = new BookManager($this->entityManager, $this->translation, $this->configFactory, $this->bookOutlineStorage);
   }
 
   /**