SQLf

SQLf is a SQL extended with fuzzy set theory application for expressing flexible (fuzzy) queries to traditional (or ″Regular″) Relational Databases. Among the known extensions proposed to SQL, at the present time, this is the most complete, because it allows the use of diverse fuzzy elements in all the constructions of the language SQL.^[1]^[2]

SQLf is the only known proposal of flexible query system allowing linguistic quantification over set of rows in queries, achieved through the extension of SQL nesting and partitioning structures with fuzzy quantifiers. It also allows the use of quantifiers to qualify the quantity of search criteria satisfied by single rows. Several mechanisms are proposed for query evaluation,^[3] the most important being the one based on the derivation principle.^[4] This consists in deriving classic queries that produce, given a threshold t, a t-cut of the result of the fuzzy query, so that the additional processing cost of using a fuzzy language is diminished.

^ Bosc, P.; Pivert, O. (1995). "SQLf: a relational database language for fuzzy querying". IEEE Transactions on Fuzzy Systems. 3 (1): 1–17. doi:10.1109/91.366566. ISSN 1063-6706.
^ Bosc, P.; Pivert, O. (2000). Knowledge Management in Fuzzy Databases. Heidelberg: Physica-Verlag HD. pp. 171–190. ISBN 978-3-7908-1865-9.
^ Bosc, P.; Pivert, O. (2000). "SQLf Query Functionality on Top of a Regular Relational Database Management System". Knowledge Management in Fuzzy Databases. Studies in Fuzziness and Soft Computing. Vol. 39. pp. 171–190. doi:10.1007/978-3-7908-1865-9_11. ISBN 978-3-7908-2467-4.
^ Bosc, Patrick; Pivert, Olivier (1995). "On the Efficiency of the Alpha-Cut Distribution Method to Evaluate Simple Fuzzy Relational Queries". Fuzzy Logic and Soft Computing. Advances in Fuzzy Systems — Applications and Theory. Vol. 4. pp. 251–260. doi:10.1142/9789812830753_0029. ISBN 978-981-02-2345-8.

[1] Bosc, P.; Pivert, O. (1995). "SQLf: a relational database language for fuzzy querying". IEEE Transactions on Fuzzy Systems. 3 (1): 1–17. doi:10.1109/91.366566. ISSN 1063-6706.

[2] Bosc, P.; Pivert, O. (2000). Knowledge Management in Fuzzy Databases. Heidelberg: Physica-Verlag HD. pp. 171–190. ISBN 978-3-7908-1865-9.

[3] Bosc, P.; Pivert, O. (2000). "SQLf Query Functionality on Top of a Regular Relational Database Management System". Knowledge Management in Fuzzy Databases. Studies in Fuzziness and Soft Computing. Vol. 39. pp. 171–190. doi:10.1007/978-3-7908-1865-9_11. ISBN 978-3-7908-2467-4.

[4] Bosc, Patrick; Pivert, Olivier (1995). "On the Efficiency of the Alpha-Cut Distribution Method to Evaluate Simple Fuzzy Relational Queries". Fuzzy Logic and Soft Computing. Advances in Fuzzy Systems — Applications and Theory. Vol. 4. pp. 251–260. doi:10.1142/9789812830753_0029. ISBN 978-981-02-2345-8.

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