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This lecture from docsity.com covers the concept of functional dependencies (fds) in database management systems. Fds represent a relationship between attributes where knowing the value of one attribute allows for the precise determination of a unique value of another attribute. The definition of functional dependency, the difference between functional dependency and derivation, and the distinction between determinants and dependents. It also provides examples of fds and discusses the importance of fds in identifying keys. Inference rules such as reflexivity, augmentation, transitivity, additivity, projectivity, and pseudotransitivity are introduced to establish certain fds from a given set of fds. The lecture concludes with an explanation of the importance of normal forms and the first normal form.
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Normalization is based on functional dependencies (FDs) A type of relationship between attributes of a relation
It does not mean that A derives B, although it may be the case sometime
Means that if we know value of A then we can precisely determine a unique value of B
Attribute of set of attributes on the left side are called determinant and on the right are called dependents Like R (a, b, c, d, e) a b, c, d d d, e
stId stName stAdr prName prCrdts S1020 Sohail Dar I-8 Islamabad MCS 64 S1038 Shoaib Ali G-6 Islamabad BCS 132 S1015 Tahira Ejaz L Rukh Wah MCS 64 S1015 Tahira Ejaz L Rukh Wah MCS 132 S1018 Arif Zia E-8, Islamabad. BIT 134
We can determine the keys of a table seeing its FDs
The determinant of an FD that determines all attributes of that table is the super key
If there is no other FD where a subset of this determinant/SK is a super key, then it is a candidate key
So FDs help to identify keys, how
EMP(eId, eName, eAdr, eDept, prId, prSal) eId eName, eDept, eAdr
eId, prId prSal STD(stId, stName, prName, adr, nic, cgpa) stId stName, prName, adr, nic, cgpa nic stName, prName, adr, stId, cgpa
If B is a subset of A then A B, it also implies that A A always hold, that is stName, stAdr stName
Or stName stName
If we have A B then
AC BC that is if stId stName then stId, stAdr stName, stAdr
If A B and A C then A BC
if empId eName and empId qual
Then we can write it as
empId eName, qual
If A BC then A B and A C if empId eName, qual Then we can write it as empId eName and empId qual
A relation is in first normal form iff every attribute in every tuple contains an atomic value
There is no multivaued (repeating group) in the relation