> If the vendor is IBM, the screenshot is probably a 5270 terminal running a RPG (or COBOL) application
From the linked PDF I gather the app is written in Informix 4GL (I can’t read Czech, just guessing based on the smattering of English words-I also think in mentions some modules are written in C?). If that’s right, it is probably a character mode VT100 app running on some Unix box, not 3270 or 5250, not COBOL or RPG