diff --git a/services/backup/docker-server/contents/server/src/DatabaseEntities/BackupItem.h b/services/backup/docker-server/contents/server/src/DatabaseEntities/BackupItem.h
index 90633bb7d..82c7b8112 100644
--- a/services/backup/docker-server/contents/server/src/DatabaseEntities/BackupItem.h
+++ b/services/backup/docker-server/contents/server/src/DatabaseEntities/BackupItem.h
@@ -1,59 +1,69 @@
 #pragma once
 
 #include "Item.h"
 
 #include <string>
 #include <vector>
 
 namespace comm {
 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;
   std::string backupID;
   uint64_t created;
   std::string recoveryData;
   std::string compactionHolder;
   std::vector<std::string> attachmentHolders;
 
   void validate() const override;
 
 public:
   static std::string tableName;
   static const std::string FIELD_USER_ID;
   static const std::string FIELD_BACKUP_ID;
   static const std::string FIELD_CREATED;
   static const std::string FIELD_RECOVERY_DATA;
   static const std::string FIELD_COMPACTION_HOLDER;
   static const std::string FIELD_ATTACHMENT_HOLDERS;
 
   BackupItem() {
   }
   BackupItem(
       std::string userID,
       std::string backupID,
       uint64_t created,
       std::string recoveryData,
       std::string compactionHolder,
       std::vector<std::string> attachmentHolders);
   BackupItem(const AttributeValues &itemFromDB);
 
   void assignItemFromDatabase(const AttributeValues &itemFromDB) override;
 
   std::string getTableName() const override;
   PrimaryKey getPrimaryKey() const override;
   PrimaryKeyValue getPrimaryKeyValue() const override;
 
   std::string getUserID() const;
   std::string getBackupID() const;
   uint64_t getCreated() const;
   std::string getRecoveryData() const;
   std::string getCompactionHolder() const;
   std::vector<std::string> getAttachmentHolders() const;
 };
 
 } // namespace database
 } // namespace network
 } // namespace comm
diff --git a/services/blob/docker-server/contents/server/src/DatabaseEntities/ReverseIndexItem.h b/services/blob/docker-server/contents/server/src/DatabaseEntities/ReverseIndexItem.h
index c6b429572..3a7727b8e 100644
--- a/services/blob/docker-server/contents/server/src/DatabaseEntities/ReverseIndexItem.h
+++ b/services/blob/docker-server/contents/server/src/DatabaseEntities/ReverseIndexItem.h
@@ -1,40 +1,45 @@
 #pragma once
 
 #include "Item.h"
 
 #include <string>
 
 namespace comm {
 namespace network {
 namespace database {
 
+/**
+ * Needs blobHash(pk)-index that projects:
+ *  blobHash
+ *  holder
+ */
 class ReverseIndexItem : public Item {
 
   std::string holder;
   std::string blobHash;
 
   void validate() const override;
 
 public:
   static std::string tableName;
   static const std::string FIELD_HOLDER;
   static const std::string FIELD_BLOB_HASH;
 
   ReverseIndexItem() {
   }
   ReverseIndexItem(const std::string holder, const std::string blobHash);
   ReverseIndexItem(const AttributeValues &itemFromDB);
 
   void assignItemFromDatabase(const AttributeValues &itemFromDB) override;
 
   std::string getTableName() const override;
   PrimaryKey getPrimaryKey() const override;
   PrimaryKeyValue getPrimaryKeyValue() const override;
 
   std::string getHolder() const;
   std::string getBlobHash() const;
 };
 
 } // namespace database
 } // namespace network
 } // namespace comm