Incomplete Information in Relational Databases
Journal of the ACM (JACM)
On the integrity of databases with incomplete information
PODS '86 Proceedings of the fifth ACM SIGACT-SIGMOD symposium on Principles of database systems
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A semantics for complex objects and approximate answers
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Semantics for null extended nested relations
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Complexity of answering queries using materialized views
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Foundations of Databases: The Logical Level
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A Graph-Oriented Object Database Model
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A Semantics-based Approach to Design of Query Languages for Partial Information
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On the decidability and complexity of query answering over inconsistent and incomplete databases
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Data exchange: semantics and query answering
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Parameterized Complexity Theory (Texts in Theoretical Computer Science. An EATCS Series)
Parameterized Complexity Theory (Texts in Theoretical Computer Science. An EATCS Series)
Conjunctive queries over trees
Journal of the ACM (JACM)
Representing and querying XML with incomplete information
ACM Transactions on Database Systems (TODS)
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Homomorphism preservation theorems
Journal of the ACM (JACM)
World-set decompositions: Expressiveness and efficient algorithms
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Datalog±: a unified approach to ontologies and integrity constraints
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The VLDB Journal — The International Journal on Very Large Data Bases
Conjunctive query containment over trees
DBPL'07 Proceedings of the 11th international conference on Database programming languages
Certain answers for XML queries
Proceedings of the twenty-ninth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
XML with incomplete information
Journal of the ACM (JACM)
Relational and XML Data Exchange
Relational and XML Data Exchange
An abstract framework for generating maximal answers to queries
ICDT'05 Proceedings of the 10th international conference on Database Theory
Efficient approximations of conjunctive queries
PODS '12 Proceedings of the 31st symposium on Principles of Database Systems
On the complexity of query answering over incomplete XML documents
Proceedings of the 15th International Conference on Database Theory
Representation systems for data exchange
Proceedings of the 15th International Conference on Database Theory
When is naive evaluation possible?
Proceedings of the 32nd symposium on Principles of database systems
Reasoning about pattern-based XML queries
RR'13 Proceedings of the 7th international conference on Web Reasoning and Rule Systems
Querying Regular Graph Patterns
Journal of the ACM (JACM)
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While incomplete information is ubiquitous in all data models - especially in applications involving data translation or integration - our understanding of it is still not completely satisfactory. For example, even such a basic notion as certain answers for XML queries was only introduced recently, and in a way seemingly rather different from relational certain answers. The goal of this paper is to introduce a general approach to handling incompleteness, and to test its applicability in known data models such as relations and documents. The approach is based on representing degrees of incompleteness via semantics-based orderings on database objects. We use it to both obtain new results on incompleteness and to explain some previously observed phenomena. Specifically we show that certain answers for relational and XML queries are two instances of the same general concept; we describe structural properties behind the naive evaluation of queries; answer open questions on the existence of certain answers in the XML setting; and show that previously studied ordering-based approaches were only adequate for SQL's primitive view of nulls. We define a general setting that subsumes relations and documents to help us explain in a uniform way how to compute certain answers, and when good solutions can be found in data exchange. We also look at the complexity of common problems related to incompleteness, and generalize several results from relational and XML contexts.