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 integrity of databases with incomplete information
PODS '86 Proceedings of the fifth ACM SIGACT-SIGMOD symposium on Principles of database systems
Evaluation of queries in independent database schemes
Journal of the ACM (JACM)
On the representation and querying of sets of possible worlds
Selected papers of the workshop on Deductive database theory
SIGMOD '94 Proceedings of the 1994 ACM SIGMOD international conference on Management of data
Hypergraph based reorderings of outer join queries with complex predicates
SIGMOD '95 Proceedings of the 1995 ACM SIGMOD international conference on Management of data
Integrating information by outerjoins and full disjunctions (extended abstract)
PODS '96 Proceedings of the fifteenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Outerjoin simplification and reordering for query optimization
ACM Transactions on Database Systems (TODS)
LORE: a Lightweight Object REpository for semistructured data
SIGMOD '96 Proceedings of the 1996 ACM SIGMOD international conference on Management of data
Queries with incomplete answers over semistructured data
PODS '99 Proceedings of the eighteenth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Outerjoin optimization in multidatabase systems
DPDS '90 Proceedings of the second international symposium on Databases in parallel and distributed systems
A simplied universal relation assumption and its properties
ACM Transactions on Database Systems (TODS)
A characterization of globally consistent databases and their correct access paths
ACM Transactions on Database Systems (TODS)
Extending the database relational model to capture more meaning
ACM Transactions on Database Systems (TODS)
On the Complexity of Testing Implications of Functional and Join Dependencies
Journal of the ACM (JACM)
Testing satisfaction of functional dependencies
Journal of the ACM (JACM)
On the Desirability of Acyclic Database Schemes
Journal of the ACM (JACM)
Degrees of acyclicity for hypergraphs and relational database schemes
Journal of the ACM (JACM)
Representing and querying XML with incomplete information
PODS '01 Proceedings of the twentieth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Object Exchange Across Heterogeneous Information Sources
ICDE '95 Proceedings of the Eleventh International Conference on Data Engineering
Extending the Algebraic Framework of Query Processing to Handle Outerjoins
VLDB '84 Proceedings of the 10th International Conference on Very Large Data Bases
The complexity of relational query languages (Extended Abstract)
STOC '82 Proceedings of the fourteenth annual ACM symposium on Theory of computing
ACM SIGMOD Record
Query-answering algorithms for information agents
AAAI'96 Proceedings of the thirteenth national conference on Artificial intelligence - Volume 1
An incremental algorithm for computing ranked full disjunctions
Proceedings of the twenty-fourth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Full disjunctions: polynomial-delay iterators in action
VLDB '06 Proceedings of the 32nd international conference on Very large data bases
An incremental algorithm for computing ranked full disjunctions
Journal of Computer and System Sciences
Maximally joining probabilistic data
Proceedings of the twenty-sixth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Matching twigs in probabilistic XML
VLDB '07 Proceedings of the 33rd international conference on Very large data bases
Generating all maximal induced subgraphs for hereditary and connected-hereditary graph properties
Journal of Computer and System Sciences
Computing full disjunction using COJO
Information Technology and Management
An abstract framework for generating maximal answers to queries
ICDT'05 Proceedings of the 10th international conference on Database Theory
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Under either the OR-semantics or the weak semantics, the answer to a query over semistructured data consists of maximal rather than complete matchings, i.e., some query variables may be assigned null values. In the relational model, a similar effect is achieved by computing the full disjunction (rather than the natural join or equijoin) of the given relations. It is shown that under either the OR-semantics or the weak semantics, query evaluation has a polynomial-time complexity in the size of the query, the database and the result. It is also shown that the evaluation of full disjunctions is reducible to query evaluation under the weak semantics and hence can be done in polynomial time in the size of the input and the output. Complexity results are also given for two related problems. One is evaluating a projection of the full disjunction and the other is evaluating the set of all tuples in the full disjunction that are non-null on some given attributes. In the special case of γ-acyclic relation schemes, both problems have polynomial-time algorithms in the size of the input and the output. In the general case, such algorithms do not exist, assuming that P ≠ NP. Finally, it is shown that the weak semantics can generalize full disjunctions by allowing tuples to be joined according to general types of conditions, rather than just equalities among attributes.