text: #ifndef MESSAGE_HPP
  #define MESSAGE_HPP
  
  #include <string>
  #include <utility>
  #include <vector>
  #include "version.hpp"
  
  //message's data structure
  struct message{
      message();
      message(std::string, std::string, version, std::vector<std::pair<std::string, version> >);
      friend bool operator < (message const &, message const &);
      std::string key;
      std::string value;
      version key_version;
      std::vector<std::pair<std::string, version> > dependencies;
  };
  
  #endif