DA0-002 Data Concepts and Environments Practice Question
A hospital's data team needs to choose a storage model for its new electronic health record (EHR) system. Patient records contain many nested, variable attributes such as a list of allergies, multiple insurance policies, and a changing set of lab results per visit. The schema changes frequently as new clinical fields are added, and the team wants to avoid costly migrations. Which data model should the team select?
⚠ Common exam trap
The trap here is assuming that any non-relational database automatically supports flexible nested schemas, when key-value stores actually treat values as opaque and offer no structure for nested attributes.
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
✓
Document model
The team needs a schema-flexible structure that can hold nested and variable attributes, such as allergy lists and changing lab results, while allowing new fields to be added without migrations. A document model provides exactly this by storing each patient record as a self-contained, nested document that evolves with clinical requirements.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Columnar model
Why it's wrong here
A columnar model organizes data by column and is optimized for large-scale analytical scans and aggregations, not for transactional record retrieval. It typically still relies on a defined schema, so frequently adding new clinical fields remains a migration task. It does not provide the nested, schema-flexible document structure this EHR system needs.
- ✗
Relational model
Why it's wrong here
A relational model stores data in fixed tables with predefined columns and enforces a rigid schema. Adding new clinical fields such as a new lab panel requires altering table structures, which is exactly the costly migration the team wants to avoid. Nested or variable attributes would need many extra tables and joins, making it a poor fit for this scenario.
- ✓
Document model
Why this is correct
A document model stores each patient record as a self-contained document that can hold nested arrays and variable fields, such as an allergy list or a set of lab results. New clinical fields can be added without altering a global schema or performing migrations, which directly matches the team's requirement for flexible, fast-changing structures.
- ✗
Key-value model
Why it's wrong here
A key-value model maps a single key to an opaque value and offers no native structure for nested attributes or querying by internal fields. Retrieving, for example, all patients with a specific allergy would require reading and parsing every value in application code, which is impractical for the complex, query-heavy EHR workload described.
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Last reviewed September 2026 · checked against the official CompTIA exam blueprint
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