Our client was a school focused on overseas students. They required a monitoring system to keep track of students classroom attendance.

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Key requirements:

• Easy-to-use UI
• High availability and tolerance to network issues
• Data privacy was of extremely high importance

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A distributed system that consists of:

On teacher's machines:

• A 'reader' service that receives data from an RFID reader and saves it into a local database
• A 'sender' service that reads data from the local DB and sends it to the main server

On the main server:

• A 'dryer' service that processes the raw data from the teachers' machines
• An ASP.NET web application to provide a UI for tutors and admins

All services were written with C#, the local database used SQLite, the main database is Postgres installed on an internal server.

As all the machines in the school used Windows, C# is the obvious choice.

SQLite is a simple and lightweight database perfect for storing intermediate data.

PostgreSQL is one of the best relational databases, and the best among free ones.