Complex sentence: PRTV (Peterlee Relational Test Vehicle) was the world's first relational database management system that could handle significant data volumes--it was really a relational query system and had very powerful query facilities, but very limited update facility and no simultaneous multiuser facility.
Split into simpler sentences: PRTV (Peterlee Relational Test Vehicle) was the world's first relational database management system that could handle significant data volumes. It was a relational query system with powerful query facilities, but very limited update facility and no simultaneous multiuser facility.