Creative Commons Attribution 4.0 International license
Relational algebra operates over relations under either set semantics or bag semantics. In 2007 Val Tannen extended the semantics of relational algebra to K-relations, where each tuple is annotated with a value from a semiring. However, only the positive fragment of the relational algebra can be interpreted over K-relations. The reason is that a semiring contains only the operations addition and multiplication, and does not have a difference operation. This paper explores three ways of adding a difference operator to a semiring: as a freely generated algebra, by using the natural order, or by an explicit construction using products and quotients. The paper consists of both a survey of results from the literature, and of some novel results.
@InProceedings{suciu:OASIcs.Tannen.10,
author = {Suciu, Dan},
title = {{Different Differences in Semirings}},
booktitle = {The Provenance of Elegance in Computation - Essays Dedicated to Val Tannen},
pages = {10:1--10:20},
series = {Open Access Series in Informatics (OASIcs)},
ISBN = {978-3-95977-320-1},
ISSN = {2190-6807},
year = {2024},
volume = {119},
editor = {Amarilli, Antoine and Deutsch, Alin},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.Tannen.10},
URN = {urn:nbn:de:0030-drops-201062},
doi = {10.4230/OASIcs.Tannen.10},
annote = {Keywords: Semirings, K-relations}
}