Fuzzy Modeling and Genetic Algorithms for Data Mining and Exploration

6.1 The Vocabulary of Relational Databases and Queries

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This is a query with three predicates in the where statement. The predi-

cates evaluate fuzzy relationships involving the project length (duration),

budget, and priority.

Primary Identifier (or Primary Key)

Each row in a table must be identified by a unique key. This is the primary

identifier. The identifier can consist of one or more contiguous columns

(if it consists of more than one column, it is a composite key). In the

projects table (Table 6.2), the project ID is the primary identifier. No

other row in the table can have the same value in this column. Note

that although usually considered a poor design it is possible for a table

to have more than one unique key (a project might also have a