April 2014 Archive

Referential Integrity Constraints

A common kind of constraint, called "referential integrity" in The Modeling of Constraints, declares that a value appearing in one context also appears in another, related context. We saw referential integrity as a matter of relationships "making sense". That is, if an object or

Additional Constraint Examples

The same constraint notation permits us to express far more than referential integrity. For instance, we can express any functional dependency as an algebraic constraint, although the notation is more awkward than the FD notation introduced in Functional Dependencies.

The Database Language SQL

The most frequently used relational DBMSs query and modify the database through a language called SQL (often pronounced sequel). SQL stands for "Structured Query Language". The portion of SQL that supports queries has capabilities very close to that of relational algebra, as

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