diff --git a/lexicons/my/spoor/content/external.json b/lexicons/my/spoor/content/external.json
index 6cd4f52..fd272af 100644
--- a/lexicons/my/spoor/content/external.json
+++ b/lexicons/my/spoor/content/external.json
@@ -9,6 +9,14 @@
         "type": "object",
         "required": [ "source", "queryable" ],
         "properties": {
+          "titles": {
+            "type": "array",
+            "minLength": 1,
+            "items": {
+              "type": "ref",
+              "ref": "my.spoor.content.defs#title"
+            }
+          },
           "source": {
             "type": "string",
             "description": "An nsid for a specific data source. The domain authority governs how to process the queryable",