Cs 6400 Exam 4 Questions With Answers

CS 6400 Exam 4 QUESTIONS WITH
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ANSWERS

Functional Dependencies - CORRECT ANSWERS ✔✔Let X and Y be |\ |\ |\ |\ |\ |\ |\ |\ |\


sets of attributes in R. Y is functionally dependent on X in R iff
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for each x in RX, there is precisely one y in RY.
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_________ determines _______ |\ |\




X --> Y
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Email --> BirthYear, CurrentCity, Salary
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Questions to ask about normalization - CORRECT ANSWERS ✔✔Is
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this relation laid out in such a manner that it is easy to enforce
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the functional dependencies that we want to enforce in the
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database?


How do we normalize the relation (or decompose into smaller
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relations) without information loss and so that the functional
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dependencies can be enforced? |\ |\ |\




Rules for normalization - CORRECT ANSWERS ✔✔no redundancy
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no cluttering of facts
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must preserve information |\ |\

,must preserve functional dependencies
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What is not a relation? - CORRECT ANSWERS ✔✔Non-first normal
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form data structures
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can contain multivalued attributes
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values of attributes in relations are pulled from sets of atomic
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values


What to do with multivalued attributes? - CORRECT ANSWERS
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✔✔Repeat the key for each multivalue attribute |\ |\ |\ |\ |\ |\ |\




i.e., if user1 has 3 interests with 3 since ages, turn the 1 row into
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3
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Problems to look for with normalization - CORRECT ANSWERS
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✔✔Redundancy
Insertion anomaly |\




Deletion anomaly |\




Update anomaly |\




Redundancy - CORRECT ANSWERS ✔✔Leads to inconsistency |\ |\ |\ |\ |\ |\




Database can be useless from the point of view of understanding
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repetitive fields
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, Insertion anomaly - CORRECT ANSWERS ✔✔occurs when certain
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attributes cannot be inserted into the database without the
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presence of other attributes, leads to many NULL values or
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duplicates


Deletion anomaly - CORRECT ANSWERS ✔✔deleting rows may
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cause a loss of data that would be needed for other future rows
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Update anomaly - CORRECT ANSWERS ✔✔improper database
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organization where a non-primary key item is stored multiple |\ |\ |\ |\ |\ |\ |\ |\ |\


times; updating the item in one location and not the others
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causes data inconsistencies
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redundant data may not be properly updated |\ |\ |\ |\ |\ |\




Information loss in normalization - CORRECT ANSWERS ✔✔getting
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more or less information from decomposing a relation into
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smaller tables that doesn't reflect reality
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Dependency Loss in normalization - CORRECT ANSWERS ✔✔If we |\ |\ |\ |\ |\ |\ |\ |\ |\


decompose a table into multiple tables, then we cannot enforce
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the functional dependencies, or may lose the ability to enforce
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them, that are split between the two relations
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dependencies should be together in the tables (Except transitive) |\ |\ |\ |\ |\ |\ |\ |\




A perfect decomposition has - CORRECT ANSWERS ✔✔no
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redundancies