Representations such as those in the dept_year relation, with one column for…
2025
Representations such as those in the dept_year relation, with one column for each value of an attribute, are called _______; they are widely used in spreadsheets and reports and in data analysis tools.
- A.
Cross-tabs
- B.
Snapshot
- C.
Both Cross-tabs and Snapshot
- D.
All of the mentioned
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Show answer & explanation
Correct answer: A
Concept
A cross-tab (also called a pivot table) is a tabular summary that takes the distinct values of one attribute and turns each of them into a separate column, with the cells holding an aggregated measure. It is a presentation/reporting structure, not a stored database object.
Application
Here the dept_year style relation is reshaped so that each distinct value of an attribute (such as each year) becomes its own column. A layout with exactly one column per value of an attribute is the definition of a cross-tab, so the blank is filled by cross-tabs.
Cross-check
Why the other terms do not fit:
Snapshot: a snapshot is a saved copy of data as it existed at a moment in time; it does not describe a one-column-per-attribute-value layout.
Because only cross-tabs matches the described layout, the combined choices that depend on snapshot also being correct cannot hold.
Cross-tabs are widely supported in spreadsheets, report writers and data-analysis tools, and SQL provides pivot features to generate them from a normal relational table.