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• Functional_dependency abstract "In relational database theory, a functional dependency is a constraint between two sets of attributes in a relation from a database.Given a relation R, a set of attributes X in R is said to functionally determine another set of attributes Y, also in R, (written X → Y) if, and only if, each X value is associated with precisely one Y value; R is then said to satisfy the functional dependency X → Y. Equivalently, the projection is a function, i.e. Y is a function of X. In simple words, if the values for the X attributes are known (say they are x), then the values for the Y attributes corresponding to x can be determined by looking them up in any tuple of R containing x. Customarily X is called the determinant set and Y the dependent set. A functional dependency FD: X → Y is called trivial if Y is a subset of X.The determination of functional dependencies is an important part of designing databases in the relational model, and in database normalization and denormalization. A simple application of functional dependencies is Heath’s theorem; it says that a relation R over an attribute set U and satisfying a functional dependency X → Y can be safely split in two relations having the lossless-join decomposition property, namely into where Z = U − XY are the rest of the attributes. (Unions of attribute sets are customarily denoted by mere juxtapositions in database theory.) An important notion in this context is a candidate key, defined as a minimal set of attributes that functionally determine all of the attributes in a relation. The functional dependencies, along with the attribute domains, are selected so as to generate constraints that would exclude as much data inappropriate to the user domain from the system as possible.A notion of logical implication is defined for functional dependencies in the following way: a set of functional dependencies logically implies another set of dependencies , if any relation R satisfying all dependencies from also satisfies all dependencies from this is usually written . The notion of logical implication for functional dependencies admits a sound and complete finite axiomatization, known as Armstrong's axioms.".
• Functional_dependency wikiPageExternalLink slides01-1.ps.
• Functional_dependency wikiPageExternalLink node10.html.
• Functional_dependency wikiPageExternalLink lec14.
• Functional_dependency wikiPageID "205784".
• Functional_dependency wikiPageRevisionID "606446793".
• Functional_dependency hasPhotoCollection Functional_dependency.
• Functional_dependency subject Category:Data_modeling.
• Functional_dependency subject Category:Database_constraints.
• Functional_dependency subject Category:Database_theory.
• Functional_dependency type Abstraction100002137.
• Functional_dependency type Attribute100024264.
• Functional_dependency type Confinement113998576.
• Functional_dependency type Constraint113998781.
• Functional_dependency type DatabaseConstraints.
• Functional_dependency type Relationship113928668.
• Functional_dependency type State100024720.
• Functional_dependency type Subjugation113996300.
• Functional_dependency comment "In relational database theory, a functional dependency is a constraint between two sets of attributes in a relation from a database.Given a relation R, a set of attributes X in R is said to functionally determine another set of attributes Y, also in R, (written X → Y) if, and only if, each X value is associated with precisely one Y value; R is then said to satisfy the functional dependency X → Y. Equivalently, the projection is a function, i.e. Y is a function of X.".
• Functional_dependency label "Dependencia funcional".
• Functional_dependency label "Dipendenza funzionale".
• Functional_dependency label "Functional dependency".
• Functional_dependency label "Functionele afhankelijkheid".
• Functional_dependency label "Funktionale Abhängigkeit".
• Functional_dependency label "Функциональная зависимость (программирование)".
• Functional_dependency label "関数従属性".
• Functional_dependency sameAs Funktionale_Abhängigkeit.
• Functional_dependency sameAs Dependencia_funcional.
• Functional_dependency sameAs Dipendenza_funzionale.
• Functional_dependency sameAs 関数従属性.
• Functional_dependency sameAs 함수_종속.
• Functional_dependency sameAs Functionele_afhankelijkheid.
• Functional_dependency sameAs m.01d5p0.
• Functional_dependency sameAs Q597053.
• Functional_dependency sameAs Q597053.
• Functional_dependency sameAs Functional_dependency.
• Functional_dependency wasDerivedFrom Functional_dependency?oldid=606446793.
• Functional_dependency isPrimaryTopicOf Functional_dependency.