TY - GEN
T1 - Fragments of Bag Relational Algebra: Expressiveness and Certain Answers
AU - Console, Marco
AU - Guagliardo, Paolo
AU - Libkin, Leonid
PY - 2019/3/19
Y1 - 2019/3/19
N2 - While all relational database systems are based on the bag data model, much of theoretical research still views relations as sets. Recent attempts to provide theoretical foundations for modern data management problems under the bag semantics concentrated on applications that need to deal with incomplete relations, i.e., relations populated by constants and nulls. Our goal is to provide a complete characterization of the complexity of query answering over such relations in fragments of bag relational algebra.The main challenges we face are twofold. First, bag relational algebra has more operations than its set analog (e.g., additive union, max-union, min-intersection, duplicate elimination) and the relationship between various fragments is not fully known. Thus we first fill this gap. Second,we look at query answering over incomplete data which again is more complex than in the set case: rather than certainty and possibility of answers, we now have numerical information about occurrences of tuples. We then fully classify the complexity of finding this information in all the fragments of bag relational algebra.
AB - While all relational database systems are based on the bag data model, much of theoretical research still views relations as sets. Recent attempts to provide theoretical foundations for modern data management problems under the bag semantics concentrated on applications that need to deal with incomplete relations, i.e., relations populated by constants and nulls. Our goal is to provide a complete characterization of the complexity of query answering over such relations in fragments of bag relational algebra.The main challenges we face are twofold. First, bag relational algebra has more operations than its set analog (e.g., additive union, max-union, min-intersection, duplicate elimination) and the relationship between various fragments is not fully known. Thus we first fill this gap. Second,we look at query answering over incomplete data which again is more complex than in the set case: rather than certainty and possibility of answers, we now have numerical information about occurrences of tuples. We then fully classify the complexity of finding this information in all the fragments of bag relational algebra.
U2 - 10.4230/LIPIcs.ICDT.2019.8
DO - 10.4230/LIPIcs.ICDT.2019.8
M3 - Conference contribution
T3 - LIPICS
BT - 22nd International Conference on Database Theory (ICDT 2019)
A2 - Barcelo, Pablo
A2 - Calautti, Marco
ER -