Net.Data uses two structures to communicate with your language environment. Your language environment must work with these structures to receive information from and to pass information to Net.Data.
Net.Data passes a structure of type dtw_lei_t to the language environment function that it calls. The structure contains, among other things, an array that contains a list of parameters to the language environment function. The language environment called by Net.Data processes the request, updates the parameters in the parameter array (if applicable), and returns to Net.Data.
Net.Data then goes through the parameter array, updates its copies of the output and input-output parameters to reflect the new values set by the language environment function, and continues processing the Net.Data macro.