1. In a relational database system for storing data in multiple rows of a relational database table, each of said rows consisting of one or more columns, apparatus for defining and enforcing one or more ordered check constraints for said table, said apparatus comprising, in combination, means for accepting the definition of an ordered check constraint from a user, said definition consisting of the specification of a sort order in which said rows may be sequenced and the specification of a logical relationship between data values stored in at least one column in a given row of said table and data value stored in at least one column of the row which is adjacent to said given row when said given row and said row adjacent to said given row are sequenced in said sort order, processing means for evaluating the data values in adjacent pairs of rows of said table to determine whether the data values in said adjacent rows satisfy said logical relationship, and means for generating a failed constraint indication whenever said processing means determines that a pair of adjacent rows in said table do not satisfy said logical relationship.