Some Properties of Query Languages for Bags

10 years 2 months ago
Some Properties of Query Languages for Bags
In this paper we study the expressive power of query languages for nested bags. We de ne the ambient bag language by generalizing the constructs of the relational language of Breazu-Tannen, Buneman and Wong, which is known to have precisely the power of the nested relational algebra. Relative strength of additional polynomial constructs is studied, and the ambient language endowed with the strongest combination of those constructs is chosen as a candidate for the basic bag language, which is called BQL (Bag Query Language). We prove that achieveing the power of BQL in the relational language amounts to adding simple arithmetic to the latter. We show that BQL has shortcomings of the relational algebra: it can not express recursive queries. In particular, parity test is not de nable in BQL. We consider augmenting BQL with powerbag and structural recursion to overcome this de ciency. In contrast to the relational case, where powerset and structural recursion are equivalent, the latter is...
Leonid Libkin, Limsoon Wong
Added 09 Aug 2010
Updated 09 Aug 2010
Type Conference
Year 1993
Where DBPL
Authors Leonid Libkin, Limsoon Wong
Comments (0)