--- /dev/null
+<?php
+
+namespace Drupal\serialization\EntityResolver;
+
+use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
+
+interface EntityResolverInterface {
+
+ /**
+ * Returns the local ID of an entity referenced by serialized data.
+ *
+ * Drupal entities are loaded by and internally referenced by a local ID.
+ * Because different websites can use the same local ID to refer to different
+ * entities (e.g., node "1" can be a different node on foo.com and bar.com, or
+ * on example.com and staging.example.com), it is generally unsuitable for use
+ * in hypermedia data exchanges. Instead, UUIDs, URIs, or other globally
+ * unique IDs are preferred.
+ *
+ * This function takes a $data array representing partially deserialized data
+ * for an entity reference, and resolves it to a local entity ID. For example,
+ * depending on the data specification being used, $data might contain a
+ * 'uuid' key, a 'uri' key, a 'href' key, or some other data identifying the
+ * entity, and it is up to the implementor of this interface to resolve that
+ * appropriately for the specification being used.
+ *
+ * @param \Symfony\Component\Serializer\Normalizer\NormalizerInterface $normalizer
+ * The Normalizer which is handling the data.
+ * @param array $data
+ * The data passed into the calling Normalizer.
+ * @param string $entity_type
+ * The type of entity being resolved; e.g., 'node' or 'user'.
+ *
+ * @return string|null
+ * Returns the local entity ID, if found. Otherwise, returns NULL.
+ */
+ public function resolve(NormalizerInterface $normalizer, $data, $entity_type);
+
+}