A relation is a two-dimensional table.
Answer: A
Correct answer: True
A relation is a two-dimensional table with the further restrictions that each cell holds a single value, all entries in a column are of one kind, no two rows are identical, and neither row nor column order carries meaning. A table meeting all of them is a relation; one that does not is merely a table.
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Each answer below shows example data from a table. Which answer is an example of the multivalue, multicolumn problem?
Answer: A
Correct answer: Three columns have the values 534-2435, 534-7867, and 546-2356 in the same row.
This is the multivalue, multicolumn problem: several values of the same attribute - here telephone numbers - held in a row of separate columns. It fails because the number of columns is fixed while the number of values is not, and because querying across them requires the same condition to be repeated for each. The values belong in a separate table, one row each.
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Multivalued dependencies should ________ be eliminated.
Answer: A
Correct answer: always
A multivalued dependency means one relation is carrying two independent multivalued facts about the same key, which forces every combination of the two to be stored and produces genuine anomalies. Splitting the relation so that each holds a single theme removes them entirely, at no cost in information, so there is no reason to tolerate one.
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