In relational database theory, a relation is best described as what kind of table?
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AColumn.
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Bone-dimensional table.
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Ctwo-dimensional table.
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Dthree-dimensional table.
Answer
Correct Answer: two-dimensional table.
Explanation
Introduction / Context:The term relation has a precise meaning in relational database theory. Understanding its structure is foundational for normalization, keys, and query formulation.
Given Data / Assumptions:
- Each relation has attributes (columns) and tuples (rows).
- Cells contain atomic values under first normal form assumptions.
- Ordering of rows and columns is not semantically important.
Concept / Approach:A relation is modeled as a two-dimensional table: one dimension for attributes (columns) and one for tuples (rows). This abstraction allows the use of operations like selection, projection, and join.
Step-by-Step Solution:
Map the definition of a relation to a rectangular arrangement of rows and columns.Confirm that there are exactly two orthogonal directions: attributes and tuples.Eliminate options that imply one or three dimensions.Verification / Alternative check:Relational algebra operations work on sets of tuples with defined attributes, consistent with a two-dimensional structure.
Why Other Options Are Wrong:
- Column or one-dimensional table: ignores the row dimension.
- Three-dimensional table: not applicable to basic relational structures; multidimensional models belong to OLAP cubes, not base relations.
Common Pitfalls:Confusing relations with multidimensional cubes or hierarchical structures. The relational model is simpler and strictly two-dimensional.
Final Answer:two-dimensional table.