DP-900 Describe core data concepts Practice Question
A data engineer is classifying data types collected from three sources for a data lake. Source 1: Customer records from a SQL database exported as CSV files with fixed columns (CustomerID, Name, Address). Source 2: Product reviews obtained via API as JSON documents with varying fields (e.g., some reviews include 'rating' and 'verified_purchase', others include 'comment'). Source 3: Scanned handwritten order forms saved as TIFF images. Which statement correctly categorizes these data by structure?
⚠ Common exam trap
Watch out — candidates often confuse CSV files (which are structured when they have a fixed schema) with semi-structured data, or assume JSON is always structured because it has key-value pairs, ignoring that varying fields make it semi-structured.
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
✓
Source 1: Structured; Source 2: Semi-structured; Source 3: Unstructured
Source 1 (CSV from SQL) has a fixed schema with defined columns, making it structured data. Source 2 (JSON from API) allows varying fields per document, which is the hallmark of semi-structured data. Source 3 (TIFF images) contains no inherent schema or machine-readable structure, classifying it as unstructured data.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Source 1: Structured; Source 2: Semi-structured; Source 3: Unstructured
Why this is correct
This is correct. Source 1 is a CSV file with fixed columns and defined data types per column, satisfying the rigid schema that defines structured data. Source 2 is JSON with varying fields; it has key-value pairs and hierarchical organization but no fixed schema, so it is semi-structured. Source 3 is TIFF images, which are binary pixel arrays without embedded field names or relational structure, making them unstructured.
- ✗
Source 1: Structured; Source 2: Structured; Source 3: Unstructured
Why it's wrong here
This is wrong because Source 2, JSON, does not meet the fixed-schema requirement for structured data. Structured data, like the CSV in Source 1, needs a predefined set of columns with consistent data types across all rows; JSON allows each object to have a different set of properties and nested constructs. While Source 1 and Source 3 are correctly labeled, labeling JSON as structured ignores its schema flexibility, which is what places it in the semi-structured category.
- ✗
Source 1: Semi-structured; Source 2: Structured; Source 3: Unstructured
Why it's wrong here
This is wrong because it swaps the classifications for Sources 1 and 2. A CSV file with fixed columns enforces the same column set and data types on every row, so it is structured, not semi-structured. JSON with varying fields is self-describing and allows each record to have different keys, nested objects, or arrays, which is the defining trait of semi-structured data, not structured. Source 3 as unstructured is correct, but the first two labels are reversed.
- ✗
Source 1: Structured; Source 2: Unstructured; Source 3: Semi-structured
Why it's wrong here
This is wrong because it reverses Sources 2 and 3. JSON data is not unstructured: it encodes meaning through named keys, nested hierarchies, and value pairs, even if the schema is inconsistent, so it belongs in the semi-structured tier. TIFF images are collections of pixel values without named fields, records, or relationships, so they are unstructured rather than semi-structured. Only Source 1, the CSV, is classified correctly here.
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Data Roles: Engineer, Analyst, Scientist, DBA
Key term
Structured data
Structured data is information that is organized in a predefined format, typically in rows and columns, making it easy to search, process, and analyze by computers.
Key term
Schema
A schema is a blueprint or logical structure that defines how data is organized, stored, and accessed in a database or information system.
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Written by Johnson Ajibi, MSc IT Security
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