diff --git a/services/backup/docker-server/contents/server/src/DatabaseEntities/BackupItem.h b/services/backup/docker-server/contents/server/src/DatabaseEntities/BackupItem.h
--- a/services/backup/docker-server/contents/server/src/DatabaseEntities/BackupItem.h
+++ b/services/backup/docker-server/contents/server/src/DatabaseEntities/BackupItem.h
@@ -9,6 +9,16 @@
 namespace network {
 namespace database {
 
+/**
+ * this class is used for representing two things: the rows in the main table,
+ * and also the rows in the secondary index
+ *
+ * Needs userID(pk)-created(sk)-index that projects:
+ *  userID
+ *  backupID
+ *  created
+ *  recoveryData
+ */
 class BackupItem : public Item {
 
   std::string userID;
diff --git a/services/blob/docker-server/contents/server/src/DatabaseEntities/ReverseIndexItem.h b/services/blob/docker-server/contents/server/src/DatabaseEntities/ReverseIndexItem.h
--- a/services/blob/docker-server/contents/server/src/DatabaseEntities/ReverseIndexItem.h
+++ b/services/blob/docker-server/contents/server/src/DatabaseEntities/ReverseIndexItem.h
@@ -8,6 +8,11 @@
 namespace network {
 namespace database {
 
+/**
+ * Needs blobHash(pk)-index that projects:
+ *  blobHash
+ *  holder
+ */
 class ReverseIndexItem : public Item {
 
   std::string holder;