The complexity of evaluating relational queries
Information and Control
A Proof Procedure for Data Dependencies
Journal of the ACM (JACM)
Elements of relational database theory
Handbook of theoretical computer science (vol. B)
Discrete Mathematics - Algebraic graph theory; a volume dedicated to Gert Sabidussi
Complexity of answering queries using materialized views
PODS '98 Proceedings of the seventeenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Logical approaches to incomplete information: a survey
Logics for databases and information systems
Navigational plans for data integration
AAAI '99/IAAI '99 Proceedings of the sixteenth national conference on Artificial intelligence and the eleventh Innovative applications of artificial intelligence conference innovative applications of artificial intelligence
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)
Data integration: a theoretical perspective
Proceedings of the twenty-first ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Foundations of Databases: The Logical Level
Foundations of Databases: The Logical Level
Reformulation of XML Queries and Constraints
ICDT '03 Proceedings of the 9th International Conference on Database Theory
Data Exchange: Semantics and Query Answering
ICDT '03 Proceedings of the 9th International Conference on Database Theory
Schema Mapping as Query Discovery
VLDB '00 Proceedings of the 26th International Conference on Very Large Data Bases
Physical Data Independence, Constraints, and Optimization with Universal Plans
VLDB '99 Proceedings of the 25th International Conference on Very Large Data Bases
Answering queries using views: A survey
The VLDB Journal — The International Journal on Very Large Data Bases
The complexity of facets (and some facets of complexity)
STOC '82 Proceedings of the fourteenth annual ACM symposium on Theory of computing
Optimal implementation of conjunctive queries in relational data bases
STOC '77 Proceedings of the ninth annual ACM symposium on Theory of computing
VLDB '02 Proceedings of the 28th international conference on Very Large Data Bases
Composing schema mappings: second-order dependencies to the rescue
PODS '04 Proceedings of the twenty-third ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Foundations of semantic web databases
PODS '04 Proceedings of the twenty-third ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
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
On preservation under homomorphisms and unions of conjunctive queries
PODS '04 Proceedings of the twenty-third ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
XML data exchange: consistency and query answering
Proceedings of the twenty-fourth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Schema mappings, data exchange, and metadata management
Proceedings of the twenty-fourth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Computing cores for data exchange: new algorithms and practical solutions
Proceedings of the twenty-fourth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Proceedings of the twenty-fourth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Determining source contribution in integration systems
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
Database repairing using updates
ACM Transactions on Database Systems (TODS)
Composing schema mappings: Second-order dependencies to the rescue
ACM Transactions on Database Systems (TODS) - Special Issue: SIGMOD/PODS 2004
Models for semantic interoperability in service-oriented architectures
IBM Systems Journal
On preservation under homomorphisms and unions of conjunctive queries
Journal of the ACM (JACM)
Data exchange: computing cores in polynomial time
Proceedings of the twenty-fifth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Data exchange and incomplete information
Proceedings of the twenty-fifth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Proceedings of the twenty-fifth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Composition of mappings given by embedded dependencies
ACM Transactions on Database Systems (TODS)
Mapping adaptation under evolving schemas
VLDB '03 Proceedings of the 29th international conference on Very large data bases - Volume 29
Efficient core computation in data exchange
Journal of the ACM (JACM)
Locality of Queries and Transformations
Electronic Notes in Theoretical Computer Science (ENTCS)
Electronic Notes in Theoretical Computer Science (ENTCS)
Schema matching and mapping: from usage to evaluation
Proceedings of the 14th International Conference on Extending Database Technology
Journal of Computer and System Sciences
Proceedings of the 4th International Workshop on Logic in Databases
Heterogeneous data translation through XML conversion
Journal of Web Engineering
Sensor data driven proactive management of infrastructure systems
EG-ICE'06 Proceedings of the 13th international conference on Intelligent Computing in Engineering and Architecture
Inconsistency tolerance in P2P data integration: an epistemic logic approach
DBPL'05 Proceedings of the 10th international conference on Database Programming Languages
DEXA'05 Proceedings of the 16th international conference on Database and Expert Systems Applications
Consistent query answers in virtual data integration systems
Inconsistency Tolerance
Representation systems for data exchange
Proceedings of the 15th International Conference on Database Theory
Data exchange in datalog is mainly a matter of choice
Datalog 2.0'12 Proceedings of the Second international conference on Datalog in Academia and Industry
A sound and complete chase procedure for constrained tuple-generating dependencies
Journal of Intelligent Information Systems
Proceedings of the 22nd ACM international conference on Conference on information & knowledge management
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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 that reflects the source data as accurately as possible. Given a source instance, there may be many solutions to the data exchange problem, that is, many target instances that satisfy the constraints of the data exchange problem. In an earlier paper, we identified a special class of solutions that we call universal. A universal solution has homomorphisms into every possible solution, and hence is a "most general possible" solution. Nonetheless, given a source instance, there may be many universal solutions. This naturally raises the question of whether there is a "best" universal solution, and hence a best solution for data exchange. We answer this question by considering the well-known notion of the core of a structure, a notion that was first studied in graph theory, but has also played a role in conjunctive-query processing. The core of a structure is the smallest substructure that is also a homomorphic image of the structure. All universal solutions have the same core (up to isomorphism); we show that this core is also a universal solution, and hence the smallest universal solution. The uniqueness of the core of a universal solution together with its minimality make the core an ideal solution for data exchange. Furthermore, we show that the core is the best among all universal solutions for answering unions of conjunctive queries with inequalities. After this, we investigate the computational complexity of producing the core. Well-known results by Chandra and Merlin imply that, unless P = NP, there is no polynomial-time algorithm that, given a structure as input, returns the core of that structure as output. In contrast, in the context of data exchange, we identify natural and fairly broad conditions under which there are polynomial-time algorithms for computing the core of a universal solution. Finally, we analyze the computational complexity of the following decision problem that underlies the computation of cores: given two graphs G and H, is H the core ofG? Earlier results imply that this problem is both NP-hard and coNP-hard. Here, we pinpoint its exact complexity by establishing that it is a DP-complete problem.