Multirelations: semantice and languages
Aviel Klausner, Nathan Goodman · Very Large Data Bases · 1985
We argue that a multirelation (relation with duplicates) is not, a semantically independent data object, but rather it should be viewed as a sub- set of columns within a larger relation that has no duplicates. Consequently, at the level of the con- ceptual database, duplicates in base relations or in views are not allowed, nor are operations on mul- tirelations. Multirelations as query output can be specified by designating a subset of some relation's columns for output, while hiding the rest of the columns. Similarly, aggregate functions are applied to multirelations by applying them to a column within a relation. Our approach can be applied to extend any query language in a consistent way to have full multirelational expressiveness, and such an extension for the query language QUEL is detailed.