Subschema usage in databases: What can subschemas (external views) be used for when presenting and securing data for different users or applications?

Introduction / Context:
The external schema (subschema) layer customizes how users and applications see the database. It supports security, usability, and performance by exposing only what is necessary in a shape that makes sense for each audience.

Given Data / Assumptions:

• Different users need different slices and shapes of the same underlying data.
• Some fields may be sensitive and must be hidden.
• Presentation can vary by context without altering the core conceptual model.

Concept / Approach:
A subschema defines a view: projected and joined columns, filtered rows, and possibly computed fields. Personalized views reduce cognitive load and enforce least-privilege access. Formats may differ (for example, denormalized report views) while the underlying data remains consistent and governed.

Step-by-Step Solution:
Map “personalized views” to external schemas tailored per role.Map “different formats” to alternative projections/joins or materialized/reporting structures.Map “hide sensitive info” to column suppression and row-level filtering in the view definition.Select the inclusive option covering all of these capabilities.

Verification / Alternative check:
RDBMS systems implement subschemas as views or schemas with granted privileges, supporting column/row filtering and customized aggregations for reporting and APIs.

Why Other Options Are Wrong:
Picking only one benefit understates subschema utility; they simultaneously enable personalization, alternative formats, and data masking.

Common Pitfalls:
Leaking sensitive columns through broad grants or ad-hoc queries; always define least-privilege views and audit access.

Final Answer:
All of the above