Functional dependency is also a property of relational schema "R" and not a particular legal relation "r" of "R".Now let us consider, a relational "a" schema "R" and let "x" and "y" be the two set of attributes, now there is a functional dependency from "x" to "y"...
What are Armstrong's Axioms in Functional Dependency in DBMS? Armstrong axiomsare a complete set of inference rules or axioms, introduced and developed byWilliam W. Armstrongin 1974. The inference rules are sound which is used to test logical inferences of functional dependencies. The axiom which...
F (w.r.t means “with respect to”关于) X (0) := X Repeat X (i+1) := X (i) Z, where Z is the set of attributes such that there exists Y Z in F, and Y X (i) Until X (i+1) := X (i) Return X (i+1) 13 Principles of DATABASE SYSTEMS, Spring 2011,guocheng ...
Starting from SQL-99, the concept of “functional dependency” was introduced; a column B is functionally dependent on columns {A1, A2} in a result set if all rows which share the same value of A1 and the same value of A2 necessarily share the same value of B. Then ...
(written as X → Y) if and only if each X value in R is associated with precisely one Y value in R; R is then said to satisfy the functional dependency X → Y. In other words, a dependency FD: X → Y means that the values of Y are determined by the values of X. Two tuple...