Mobile operators and their tariffs

Mobile operators and their tariffs.
The Opportunities.
Adding tariff operators and users.
Adding tariffs to the existing operator.
Adding tariffs to the user.
View all operators with information about the total number of users from the operator.
and the number of users by each operator's tariff.
View all users with their tariffs.
Check the tariffs sorted by cost.
Search for tariffs according to the terms.
It is all stored and downloaded from a text file.