A construct containing copies of original values and backreferences to their original rows. Not part of the SQL standard.

• A. Primary Key
• B. Cache
• C. Index
• D. Snapshot

Answer: (C)

An index in a database is a separate data structure that stores copies of the indexed column values along with a pointer to the row where that value appears. This lets the database quickly locate rows without scanning the whole table, because each key value in the index is tied to the exact row via that reference. The description matches this idea: copies of original values plus backreferences to their original rows. The SQL standard doesn’t dictate a specific internal index design, as indexing is an implementation detail handled by the database engine.

The other options don’t fit as well. A primary key is a constraint that ensures a unique identifier for each row, not a separate structure that maps values to row locations. A cache stores frequently accessed data in memory to speed repeated access, but it’s not a structured index with pointers to rows. A snapshot is a fixed view of data at a moment in time, not a data structure linking values to their actual rows.