Complex sentence: There is a big difference between DMSII and modern Relational Databases: in DMSII a record can only be retrieved via an index if the index was designed initially, or after a massive reorganization that generates a new subset from all the data in the set.
Split into simpler sentences: There is a big difference between DMSII and modern Relational Databases. In DMSII you can only retrieve a record via an index If you designed it, initially or after a massive reorganization that generates a new subset from all the data in the set.