To put the Student relation in BCNF, we would have to create a new Room relation in which dorm room number
was the key and Dorm was a nonkey attribute.
Normal forms exist at even higher levels. In ascending order, the forms are fourth normal form, fifth normal
form, and domain key normal form. In day-to-day work with databases, one is less likely to focus on these
higher forms, so this chapter will end its discussion of normalization with BCNF. The important guide to
remember is that each relation should embrace a single theme, a single topic.
SQL??”STRUCTURED QUERY LANGUAGE
IBM first brought SQL to database processing. It is a high-level language for creating databases,
manipulating data, and retrieving sets of data. SQL is a nonprocedural language??”that is, SQL statements
describe the data and operations of interest, but do not specify in detail how the underlying database system
is to satisfy the request.
CHAP. 8] DATABASE 147
Figure 8-5 3NF.
ANSI standards for SQL were published in 1986, 1989, 1992, 1999, and 2003. In practice, different database
vendors offer SQL with small differences in syntax and semantics. For any particular vendor, most SQL
statements will conform to the standard, and there will also be numerous small differences.
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