GATE CS 2013 Q15 — File Organization and Indexing (B and B+ Trees)

By definition, a clustered index is an index where the physical order of the data records in the storage file is the same as the logical order of the index entries.

Let's analyze the options:

• Option A & B: An index can be created on any attribute(s), whether they form a candidate/primary key or not. While a clustered index is often created on the primary key, it is not a defining requirement. For example, a clustered index can be created on a non-key attribute (often called a clustering index).
• Option C: This is the exact definition of a clustered index. Since the physical file is ordered according to the index key, the data records and index entries share the same ordering.
• Option D: This describes an unclustered (or secondary) index, where the physical organization of the data records does not match the order of the index entries.

Therefore, the correct option is C.