Information system based language (ISBL) is a pure relational algebra based query language, which was developed in IBM’s Peterlee Centre in UK in 1973. It was first used in an experimental interactive database management system called Peterlee Relational Test Vehicle (PRTV). Using ISBL, a database system can be created with a size of about 50 relations, each containing at most 65,000 tuples. Each tuple can have at most 128 columns. Table 5.2 shows the correspondence of syntax of ISBL and relational algebra for relations R and S. In both ISBL and relational algebra, R and S can be any relational expression, and F is a Boolean formula.