Incomplete Information in Relational Databases
Journal of the ACM (JACM)
Set-theoretic problems of null completion in relational databases
Information Processing Letters
Statistical analysis with missing data
Statistical analysis with missing data
Fuzzy relational algebra for possibility-distribution-fuzzy-relational model of fuzzy data
Journal of Intelligent Information Systems
Management of uncertainty in database systems
Modern database systems
Extending the database relational model to capture more meaning
ACM Transactions on Database Systems (TODS)
FQUERY for Access: towards human consistent querying user interface
SAC '96 Proceedings of the 1996 ACM symposium on Applied Computing
A relational model of data for large shared data banks
Communications of the ACM
Fuzziness in Database Management Systems
Fuzziness in Database Management Systems
Principles and Applications
Foundations of Databases: The Logical Level
Foundations of Databases: The Logical Level
Fuzzy Database Modeling
Recent Issues on Fuzzy Databases
Recent Issues on Fuzzy Databases
Null values in data base management a denotational semantics approach
SIGMOD '79 Proceedings of the 1979 ACM SIGMOD international conference on Management of data
Can we use the universal instance assumption without using nulls?
SIGMOD '81 Proceedings of the 1981 ACM SIGMOD international conference on Management of data
Possibility Theory, Probability Theory and Multiple-Valued Logics: A Clarification
Annals of Mathematics and Artificial Intelligence
Conjunctive Aggregation of Extended Possibilistic Truth Values and Flexible Database Querying
FQAS '02 Proceedings of the 5th International Conference on Flexible Query Answering Systems
A Server for Fuzzy SQL Queries
FQAS '98 Proceedings of the Third International Conference on Flexible Query Answering Systems
Approaches for Updating Databases With Incomplete Information and Nulls
Proceedings of the First International Conference on Data Engineering
Modelling uncertainty in multimedia database systems: an extended possibilistic approach
International Journal of Uncertainty, Fuzziness and Knowledge-Based Systems
Advances In Fuzzy Object-oriented Databases: Modeling And Applications
Advances In Fuzzy Object-oriented Databases: Modeling And Applications
Toward a generalized theory of uncertainty (GTU): an outline
Information Sciences—Informatics and Computer Science: An International Journal
Fuzzy sets in database and information systems: Status and opportunities
Fuzzy Sets and Systems
Calculating attribute values using inheritance structures in fuzzyobject-oriented data models
IEEE Transactions on Systems, Man, and Cybernetics, Part C: Applications and Reviews
Aggregating constraint satisfaction degrees expressed by possibilistic truth values
IEEE Transactions on Fuzzy Systems
About projection-selection-join queries addressed to possibilistic relational databases
IEEE Transactions on Fuzzy Systems
SQLf: a relational database language for fuzzy querying
IEEE Transactions on Fuzzy Systems
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Since in the real world, it often occurs that information is missing, database systems clearly need some facilities to deal with missing data. With respect to traditional database systems, the most commonly adopted approach to this problem is based on null values and three valued logic. This paper deals with the semantics and the use of null values in fuzzy databases. In dealing with missing information a distinction is made between incompleteness due to unavailability and incompleteness due to inapplicability. Both the database modelling and database querying aspects are described. With respect to attribute values, incompleteness due to unavailability is modelled by possibility distributions, which is a commonly used technique in the fuzzy databases. Domain specific null values, represented by a bottom symbol, are used to model incompleteness due to inapplicability. Extended possibilistic truth values are used to formalize the impact of data manipulation and (flexible) querying operations in the presence of these null values. The different cases of appearances of null values in the handling of selection conditions of flexible database queries are described in detail.