A Proof Procedure for Data Dependencies
Journal of the ACM (JACM)
Incomplete Information in Relational Databases
Journal of the ACM (JACM)
Discrete Mathematics - Algebraic graph theory; a volume dedicated to Gert Sabidussi
On a monadic NP vs monadic co-NP
Information and Computation
Counting quantifiers, successor relations, and logarithmic space
Journal of Computer and System Sciences - special issue on complexity theory
Consistent query answers in inconsistent databases
PODS '99 Proceedings of the eighteenth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Testing implications of data dependencies
ACM Transactions on Database Systems (TODS)
EXPRESS: a data EXtraction, Processing, and Restructuring System
ACM Transactions on Database Systems (TODS)
Horn clauses and database dependencies
Journal of the ACM (JACM)
Counting modulo quantifiers on finite structures
Information and Computation - Special issue: LICS 1996—Part 1
Data integration: a theoretical perspective
Proceedings of the twenty-first ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Elements Of Finite Model Theory (Texts in Theoretical Computer Science. An Eatcs Series)
Elements Of Finite Model Theory (Texts in Theoretical Computer Science. An Eatcs Series)
Locally consistent transformations and query answering in data exchange
PODS '04 Proceedings of the twenty-third ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Data exchange: getting to the core
ACM Transactions on Database Systems (TODS) - Special Issue: SIGMOD/PODS 2003
Schema mappings, data exchange, and metadata management
Proceedings of the twenty-fourth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Data exchange: semantics and query answering
Theoretical Computer Science - Database theory
Efficient core computation in data exchange
Journal of the ACM (JACM)
Answering aggregate queries in data exchange
Proceedings of the twenty-seventh ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Logical foundations of relational data exchange
ACM SIGMOD Record
Relational and XML Data Exchange
Relational and XML Data Exchange
Data exchange and schema mappings in open and closed worlds
Journal of Computer and System Sciences
ACM Transactions on Database Systems (TODS)
Local transformations and conjunctive-query equivalence
PODS '12 Proceedings of the 31st symposium on Principles of Database Systems
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Data exchange is the problem of taking data structured under a source schema and creating an instance of a target schema. Given a source instance, there may be many solutions - target instances that satisfy the constraints of the data exchange problem. Previous work has identified two classes of desirable solutions: canonical universal solutions, and their cores. Query answering in data exchange amounts to rewriting a query over the target schema to another query that, over a materialized target instance, gives the result that is semantically consistent with the source (specifically, the ''certain answers''). Basic questions are then: (1) how do these solutions compare in terms of query rewriting? and (2) how can we determine whether a query is rewritable over a particular solution? Our goal is to answer these questions. Our first main result is that, in terms of rewritability by relational algebra queries, the core is strictly less expressive than the canonical universal solution, which in turn is strictly less expressive than the source. To develop techniques for proving queries non-rewritable, we establish structural properties of solutions; in fact they are derived from the technical machinery developed in the rewritability proofs. Our second result is that both the canonical universal solution and the core preserve the local structure of the data, and that every target query rewritable over any of these solutions cannot distinguish tuples whose neighborhoods in the source are similar. This gives us a first simple tool for checking whether a query is non-rewritable over the canonical universal solution or over the core. We also show that these tools generalize to arbitrary transformations that preserve the local structure of the data, and investigate an alternative semantics of query answering in data exchange.