Refining Database Systems

Most computers are used in an organisational setting and most organisational information systems are database systems. A database system is one in which the simple statements far outnumber the complex ones, to the extent that a special database management system is required to enable sufficiently rapid access to the data thus stored. SQL is the standard language for database access and manipulation. Z is a formal notation which has achieved some degree of acceptance — even popularity. Yet, Z and SQL are rarely considered in conjunction, which is unfortunate because both languages have their roots in set theory and predicate calculus. This paper examines some of the issues involved in mapping from a Z specification to an SQL-based implementation.