functional dependency


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Related to functional dependency: normalization, Transitive dependency

functional dependency

(database)
Given a relation R (in a relational database), attribute Y of R is functionally dependent on attribute X of R and X of R functionally determines Y of R (in symbols R.X -> R.Y) if and only if each X in R has associated with it precisely one Y in R (at any one time). Attributes X and Y may be composite.

This is very close to a function in the mathematical sense.

functional dependency

A dependent relationship between two data elements in a relational database. Used to define normalization, a functional dependency (FD) states that one data element is dependent on another. For example, a social security number (SSN) refers to only one employee (EMP). Expressed as SSN->EMP, employee is dependent on social security number. A product number refers to one product (PRODNO->PRODNAME), and a customer number refers to one customer name (CUSTNO->CUSTNAME). See normalization and transitive dependency.
References in periodicals archive ?
From the view of approval or disproval of the above mentioned hypothesis H3 it may be stated that the positive functional dependency between the use of external finance sources and return on equity is apparent in Czech, Hungarian and Polish companies.
To check if a functional dependency Y [right arrow] A holds in a set of dependencies F, we compute the closure of Y and check If A [subset or equal to] [Y.
A functional dependency composite score (ranging from 2-7) was calculated for each subject by summing the pre-operative functional status and post-operative gait and bed mobility functional scores to provide each individual a global functional performance measure, where higher scores indicated greater dependency.
A four-factor mixed ANOVA was conducted for functional dependency, alarm number, participant's expertise, and repeated exposure.
This study examined the effects of post-hospital Medicare home health and informal care on patients' subsequent functional dependency.
As our theorems show, it is especially important to compress the set of automata for which the functional dependency graph is cyclic.
Age (20-103 years) Sex (1 =Male) Ethnicity (1=Minority) Functional Dependency Scale (-2.
Thus, the considered insertion violates functional dependency sId, pId [arrow] delivPlace defined in [R.
We now introduce the notion of temporal functional dependency (TFD).
Any form field designated as a determinant in a functional dependency represents an entity (e.
By introducing a fuzzy resemblance measure EQUAL for comparing domain values, the definition of classical functional dependency has been generalized to fuzzy functional dependency (ffd).
A TFD is a proper extension of the traditional functional dependency and takes the form X [right arrow.

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