An inverted file :

The correct answer is option 1: An Inverted file is an index data structure that maps content to its location within a database file, in a document or in a set of documents.

Key Points

• An inverted file (or inverted index) is a widely used data structure in information retrieval systems and search engines.
• It stores a mapping from content (such as a word or term) to its **locations** in a set of documents or database records.
• This allows for fast full-text searches and efficient query processing.
• Each term in the index is associated with a list of document IDs or locations where it appears.

Additional Information

• Option 2: Too vague; does not describe the indexing or mapping function of inverted files.
• Option 3: Incorrect; inverted files are not inherently read-only.
• Option 4: Incorrect, since option 1 is valid and correct.

Hence, the correct answer is: option 1