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Relational Database Exam Questions Solved 100% Correct
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Relational Database Exam QuestionsSolved 100% Correct
1) What is functional dependency - ANSWER An Attribute Y is Functionally Dependent on an
Attribute X, if a Value for X Determines a Unique Value for Y. X may be a Set of Attributes.
Functional Dependency Example: Employee NumberEmployee Name.
2) What is a full functional dependency - ANSWER An Attribute Y may be Determined by a Set
of Attributes A, B, C (ABCY). If X is a set of Attributes Such That XY and there is no Subset Z of
X so that ZY, then Y is Fully Functionally Dependent on X. Full FD Example: Employee Number,
Dept Employee Name, But Employee Number Employee Name So Employee Name is not Fully
Functionally Dependent on Employee Number and Department
3) What is a transitive dependency - ANSWER Let X, Y, and Z be Attributes such that XY and YZ.
Then a Transitive Dependency Exists Between X and Z such that XZ. Transitive Dependency
Example Employee Number Dept Dept Head. A Transitive Dependency Exists Between
Employee Number and Department Head
Describe the first three normal forms, First Normal Form (1NF) - ANSWER All Data Values Are
Atomic, No Composite Fields, and No Repeating Groups;
Normal Form (2NF) - ANSWER If and Only If All Non
Key Attributes Are Fully Functionally Dependent on The Relation Key. - ANSWER
Third Normal Form (3NF) - ANSWER a Relation is in Third Normal Form if there are no
Transitive Dependencies Between Non
key Attributes. Fourth and Fifth Normal Forms Address Relations that Contain Multi - ANSWER
,Valued Dependencies. - ANSWER
4) Conceptually, what is the difference between normalization via decomposition and
normalization via synthesis - ANSWER Normalization via Decomposition Begins with existing
tables and breaks them down into smaller table. Normalization via Synthesis Begins with Data
Dependencies and aggregates them into table.
5) For each of Armstrong's Axioms, give an example in plain English. Armstrong's Axioms -
ANSWER a. Functional dependency is similar to logical implication
b. Develop a mathematical basis for database design developing a set of axioms for
function dependency.
Reflexive Rule - ANSWER XX
c. Every attribute determines itself
d. Given an Employee number, I can give you a unique employee number that is the one
you gave me.
Augmentation Rule - ANSWER If XY, Then XZY for any Z
e. If employee number determines name, the employee number and any other attribute
will determine name.
f. This is why candidate key requires minimality, otherwise there would be infinitely
many candidate keys.
Union Rule - ANSWER If XY, and XZ, then XYZ
g. If employee # determine name and address, then the employee number determines a unique
pair of name and address.
Decomposition Rule - ANSWER If XY, then XZ where Z is a subset of Y.
h. If employee number determines a set of attributes such as (name, address, phone, etc.)
then it uniquely determine any subset of such as (name, address)
i. This allows us to access columns by the key
, Transitivity Rule - ANSWER If XY and YZ, then XZ
j. If employee # determines department and department determine manager, then employee
# determines manager
k. Third Normal Form
Pseudo Transitivity Rule - ANSWER If XY and YZW, then XZW
l. If employee # determine pay grade and pay grade with current schedule determines salary,
then employee number and current schedule determine salary.
6) What is the closure of a set of functional dependencies - ANSWER Closure of F: Let F be a set
of functional dependencies. The closure of F, denoted F+, is the set of all function dependencies
that can be derived from F using Armstrong's Axioms. Every possible question that can be asked
of that database
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