DA0-002 Data Concepts and Environments Practice Question
A retail company stores customer purchase history in a relational database. The database contains a table 'transactions' with columns: transaction_id, customer_id, product_id, quantity, price, and transaction_date. A data analyst needs to create a report that shows total revenue per customer for the last quarter. Which data concept describes the relationship between customer_id and total revenue?
⚠ Common exam trap
CompTIA often tests the confusion between a derived attribute (computed from other attributes) and a foreign key (a referential constraint), leading candidates to incorrectly select 'foreign key' because customer_id appears in multiple tables.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Derived attribute
Total revenue is calculated by summing (quantity * price) for each customer, making it a derived attribute because it is computed from existing stored data (quantity and price) rather than stored directly. In the context of the 'transactions' table, customer_id is a stored key, but total_revenue is not stored; it is derived via aggregation, which matches the definition of a derived attribute in database design.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Foreign key
Why it's wrong here
A foreign key enforces referential integrity between tables; here customer_id already exists in transactions, and total revenue is a computed aggregate, not a key relationship. Foreign keys are correct when linking child rows to a parent table, not when describing derivation of a measure.
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Composite attribute
Why it's wrong here
Composite attributes decompose into sub-parts, such as a full name splitting into first and last; total revenue is a derived aggregate, not a composite. Composite attributes are the right concept when modelling a single attribute with meaningful internal structure, not a computed sum grouped by customer.
- ✓
Derived attribute
Why this is correct
Total revenue is not stored but computed by aggregating quantity multiplied by price grouped by customer_id. Because it is calculated from existing stored columns rather than persisted, it is a derived attribute, satisfying the report's need for per-customer revenue.
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Atomic attribute
Why it's wrong here
Atomic attributes cannot be subdivided further, such as a single price value; total revenue is a calculated aggregate across many rows, so atomicity does not describe it. Atomic attributes are correct when modelling indivisible stored values, not a derived sum grouped by customer.
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