File organization methods: Which option best describes a direct-access (random) file organization approach?

Introduction / Context:
Choosing a file organization affects retrieval speed, update cost, and storage overhead. Common strategies include sequential, indexed-sequential, and direct (random) access. Understanding their differences guides design decisions for batch processing versus real-time lookup workloads.

Given Data / Assumptions:

• Direct access aims at fast retrieval of any record without scanning from the beginning.
• Data placement can be computed (e.g., hashing) or mapped via addresses.
• Indexing and sequential storage are related but distinct approaches.

Concept / Approach:
In direct-access (random) organization, records are stored so that their location can be determined directly (e.g., via a hashing function on a key) rather than by scanning a sequence. This permits near-constant-time retrievals under good distribution. By contrast, sequential stores in key order and favors batch reads, and indexed-sequential keeps a sequence with an index to speed lookups while preserving order for range scans.

Step-by-Step Solution:

Verification / Alternative check:
Hash files and certain key-to-address schemes exemplify direct access; they compute a storage address from the key and read the record immediately.

Why Other Options Are Wrong:

• Contiguous blocks by key: Sequential, not random.
• Sequential with index: Indexed-sequential, not direct.
• Separate index for each key type: Describes indexing strategy, not direct placement logic.

Common Pitfalls:
Assuming any index implies direct access; confusing hash-based direct organization with B-tree indexed-sequential files.

Final Answer:
Placing records non-sequentially so that any record can be accessed directly