On the representation and querying of sets of possible worlds
SIGMOD '87 Proceedings of the 1987 ACM SIGMOD international conference on Management of data
PODS '89 Proceedings of the eighth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Imprecise information and uncertainty in information systems
ACM Transactions on Information Systems (TOIS)
Error propagation in distributed databases
CIKM '95 Proceedings of the fourth international conference on Information and knowledge management
A statistical approach to incomplete information in database systems
ACM Transactions on Database Systems (TODS)
A Hybrid Representation of Vague Collections for Distributed Object Management Systems
IEEE Transactions on Knowledge and Data Engineering
Partial Answers for Unavailable Data Sources
FQAS '98 Proceedings of the Third International Conference on Flexible Query Answering Systems
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Query processing on partly inaccessible databases generally does not yield exact, but vague result sets. A good notion of vague sets fulfills two aims: It keeps the degree of vagueness of the query result as small as possible, and it clarifies the degree of and the reasons for the vagueness to the end user. The first goal requires a good internal representation, while the second goal requires a good external representation of a vague set. In this paper, we present a novel calculus for expressive vague sets that meets both requirements. This is the first approach that is well suited for both internal and external representation of vagueness induced by partial inaccessibility. It consists of a data representation that is capable of holding all the necessary information. Complementary, we have accordingly adapted the usual query language operations. These adaptations are independent of a concrete query language, to make them applicable to most existing query languages. The adapted operations minimize the vagueness of the result, propagate the reasons of uncertainty of the individual vague candidates, and compute an expressive description of the missing elements.