Complex sentence: It have been operating as a separate company since 1 November 1999, when owing to the resolution of Szczecin city concil, the company was separated from MZK Szczecin.
Split into simpler sentences: It have been operating as a separate company since 1 November 1999. That day, according to to the resolution of Szczecin city concil, the company was separated from MZK Szczecin.