Surveillance data reaches air traffic management software as a stream of binary messages in ASTERIX, EUROCONTROL's exchange format: system tracks, safety-net alerts, status messages, each category with its own layout and its own editions. Software that uses the stream has to decode every message, keep pace with the traffic and turn tracks into flights before it can say anything useful about them.
It also has to live next to operational systems that must not be disturbed. It is often installed on a closed network, where nothing can be downloaded, and it has to be tested without touching the live feed. When it finds a safety event, an investigator needs to see exactly what happened, weeks later, from the recorded data.