Incomplete Information in Relational Databases
Journal of the ACM (JACM)
A sound and sometimes complete query evaluation algorithm for relational databases with null values
Journal of the ACM (JACM)
On the representation and querying of sets of possible worlds
Selected papers of the workshop on Deductive database theory
Discrete Mathematics - Algebraic graph theory; a volume dedicated to Gert Sabidussi
ACM SIGMOD Record
Problem of Incomplete Information in Relational Databases
Problem of Incomplete Information in Relational Databases
Foundations of Databases: The Logical Level
Foundations of Databases: The Logical Level
On the decidability and complexity of query answering over inconsistent and incomplete databases
Proceedings of the twenty-second ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Optimal implementation of conjunctive queries in relational data bases
STOC '77 Proceedings of the ninth annual ACM symposium on Theory of computing
Kleisli, a functional query system
Journal of Functional Programming
Constraint-based XML query rewriting for data integration
SIGMOD '04 Proceedings of the 2004 ACM SIGMOD international conference on Management of data
Foundations of semantic web databases
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
XML Queries and constraints, containment and reformulation
Theoretical Computer Science - Database theory
Data exchange: semantics and query answering
Theoretical Computer Science - Database theory
Composing schema mappings: Second-order dependencies to the rescue
ACM Transactions on Database Systems (TODS) - Special Issue: SIGMOD/PODS 2004
Conjunctive queries over trees
Journal of the ACM (JACM)
Representing and querying XML with incomplete information
ACM Transactions on Database Systems (TODS)
Model management 2.0: manipulating richer mappings
Proceedings of the 2007 ACM SIGMOD international conference on Management of data
VLDB '02 Proceedings of the 28th international conference on Very Large Data Bases
Matching twigs in probabilistic XML
VLDB '07 Proceedings of the 33rd international conference on Very large data bases
XML data exchange: Consistency and query answering
Journal of the ACM (JACM)
Modeling and querying probabilistic XML data
ACM SIGMOD Record
Logical foundations of relational data exchange
ACM SIGMOD Record
Proceedings of the twenty-eighth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
XML with incomplete information: models, properties, and query answering
Proceedings of the twenty-eighth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Conjunctive query containment over trees
DBPL'07 Proceedings of the 11th international conference on Database programming languages
On the tradeoff between mapping and querying power in XML data exchange
Proceedings of the 13th International Conference on Database Theory
Incomplete information and certain answers in general data models
Proceedings of the thirtieth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Tractable XML data exchange via relations
Proceedings of the 20th ACM international conference on Information and knowledge management
On the complexity of query answering over incomplete XML documents
Proceedings of the 15th International Conference on Database Theory
Between tree patterns and conjunctive queries: is there tractability beyond acyclicity?
MFCS'12 Proceedings of the 37th international conference on Mathematical Foundations of Computer Science
Certain and possible XPath answers
Proceedings of the 16th International Conference on Database Theory
Reasoning about pattern-based XML queries
RR'13 Proceedings of the 7th international conference on Web Reasoning and Rule Systems
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The notion of certain answers arises when one queries incompletely specified databases, e.g., in data integration and exchange scenarios, or databases with missing information. While in the relational case this notion is well understood, there is no natural analog of it for XML queries that return documents. We develop an approach to defining certain answers for such XML queries, and apply it in the settings of incomplete information and XML data exchange. We first revisit the relational case, and show how to present the key concepts related to certain answers in a new model-theoretic language. This new approach naturally extends to XML. We prove a number of generic, application-independent results about computability and complexity of certain answers produced by it. We then turn our attention to a pattern-based XML query language with trees as outputs, and present a technique for computing certain answers that relies on the notion of a basis of a set of trees. We show how to compute such bases for documents with nulls and for documents arising in data exchange scenarios, and provide complexity bounds. While in general complexity of query answering in XML data exchange could be high, we exhibit a natural class of XML schema mappings for which not only query answering, but also many static analysis problems can be solved efficiently.