A business rule applying to one or more columns in a table that defines the valid values for those columns. For example, a column value cannot be null, or it must have one of a predefined set of values (as in state or area codes), or it must be in a certain numeric range, or it must exist in another table (as in foreign key). Integrity constraints are defined for a column when the table is created or altered. There are six possible types (CHECK, UNIQUE, PRIMARY, FOREIGN, DEFAULT, and NULL).
a first order formula in restricted quantification form in which only the pre defined predicate symbols of the terminological and object components plus the usual equality and inequality symbols may occur