This project implements a client-servers system which accepts / rejects various user travel requests and handles queries based on their vaccination records. We have one travelMonitorClient client process which uses sockets to communicate with a number of travelMonitorServer server processes using a self-designed communication protocol. The vaccination records / data are read using a number of threads created by the server processes. Sample vaccination data can be found in folder /input_dir. Detailed information about the project's specifications can be found in the project's pdf file : hw2-spring-2021.pdf, in greek.