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.
This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)

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.
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Stroke severity, physical disability, and functional dependency are the most common risk factors for PSD.
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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.
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[X.sup.+]: = X While there is a fd Y [right arrow] A [member of] F If Y [subset or equal to] [X.sup.+] and A [??] [X.sup.+] then [X.sup.+] : = [X.sup.+] [union] A End if End while 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.sup.+].
An algorithmic approach to database normalization
Specifically, the relationships among APTI, LOS, and functional dependency were analyzed.
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In total, there were 19 presentations in each of two blocks of trials: nine levels of functional dependency for the two alarm groups plus one presentation of a labeled test alarm alone.
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In contrast, variations in the amounts of postacute Medicare home health services that patients receive had an insignificant effect on functional dependency six weeks after discharge.
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If there is no cycle in the functional dependency graph then we can apply Theorem 5.11; otherwise we must resort to Theorem 5.13.
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It is important to notice that a data relatability dependency is related to a functional dependency. If ||[M.sub.A]|| = 1 (the cardinality of the mapping is 1) then the definition of data relatability dependency is equivalent to the definition of a functional dependency.
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Based on a review of the correlation matrix, ADL, IADL, and MMSE were combined into a single measure referred to hereafter as functional dependency. The functional dependency index was created by standardizing each of the three variables, adding the standardized variables together, and then standardizing the resulting dependency index.
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If it is accepted that the problem of nonsimplicity is the problem of multivalued dependency without functional dependency, then one would conjecture that if the problem of nonsimplicity is taken care of, then the only remaining problem is that of functional dependency.
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