Journal
ACM TRANSACTIONS ON DATABASE SYSTEMS
Volume 43, Issue 1, Pages -Publisher
ASSOC COMPUTING MACHINERY
DOI: 10.1145/3183673
Keywords
Bounded rewriting; big data; complexity
Funding
- NSFC [61602023, 61421003]
- ERC [652976]
- 973 Program [2014CB340302]
- EPSRC [EP/M025268/1]
- Shenzhen Peacock Program [1105100030834361]
- Beijing Advanced Innovation Center for Big Data and Brain Computing
- Foundation for Innovative Research Groups of NSFC
- Huawei Technologies
- EPSRC [EP/M025268/1] Funding Source: UKRI
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A query Q in a language L has a bounded rewriting using a set of L-definable views if there exists a query Q' in L such that given any dataset D, Q(D) can be computed by Q' that accesses only cached views and a small fraction D-Q of D. We consider datasets D that satisfy a set of access constraints, which are a combination of simple cardinality constraints and associated indices, such that the size |D-Q| of D-Q and the time to identify D-Q are independent of |D|, no matter how big D is. In this article, we study the problem for deciding whether a query has a bounded rewriting given a set V of views and a set A of access constraints. We establish the complexity of the problem for various query languages L, from Sigma(p)(3)-complete for conjunctive queries (CQ) to undecidable for relational algebra (FO). We show that the intractability for CQ is rather robust even for acyclic CQ with fixed V and A, and characterize when the problem is in PTIME. To make practical use of bounded rewriting, we provide an effective syntax for FO queries that have a bounded rewriting. The syntax characterizes a key subclass of such queries without sacrificing the expressive power, and can be checked in PTIME. Finally, we investigate L-1-to-L-2 bounded rewriting, when Q in L-1 is allowed to be rewritten into a query Q' in another language L-2. We show that this relaxation does not simplify the analysis of bounded query rewriting using views.
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