Star Schema Design Considerations in Power BI
Which THREE factors should you consider when designing a star schema in Power BI?
Quick Answer
The answer is that dimension tables should be denormalized, a separate date table is required, and fact tables should contain only foreign keys and measures. Denormalization in dimension tables reduces the number of joins and improves query performance by flattening hierarchies like time or geography into a single table, which is critical for star schema design considerations in Power BI. A dedicated date table is mandatory because DAX time intelligence functions such as TOTALYTD require a continuous, gap-free date range to calculate correctly across all granularities. On the PL-300 exam, this tests your understanding of how star schemas optimize data models for both speed and DAX functionality—a common trap is assuming you can use a date column directly from a fact table. Remember the mnemonic: “Dims are flat, facts are thin, dates must be a table within.”
⚠ Common exam trap
Test-takers frequently confuse the theoretical normalization benefits of a snowflake schema (reducing redundancy) with the practical performance requirements of Power BI, where denormalization and surrogate keys are essential for optimal query execution and time intelligence calculations.
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
✓
A separate date table should be created for time intelligence.
A separate date table is required for time intelligence functions in Power BI because DAX time intelligence functions (e.g., TOTALYTD, SAMEPERIODLASTYEAR) rely on a continuous, contiguous date range with no gaps. Power BI automatically marks a table as a date table only if it contains a complete set of dates from the earliest to the latest transaction, enabling functions like DATEADD and DATESBETWEEN to work correctly across all granularities.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
A separate date table should be created for time intelligence.
Why this is correct
A dedicated date table enables time-based calculations.
- ✗
Use natural keys instead of surrogate keys in dimension tables.
Why it's wrong here
Surrogate keys are preferred for stability and performance.
- ✓
Fact tables should contain only foreign keys and numeric measures.
Why this is correct
This minimizes table size and improves aggregation.
- ✗
Use a snowflake schema to reduce data redundancy.
Why it's wrong here
Snowflake schemas are generally not recommended in Power BI due to performance overhead.
- ✓
Dimension tables should be denormalized.
Why this is correct
Denormalized dimensions reduce the number of tables and improve query performance.
Go deeper
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Same concept, more angles
1 more way this is tested on PL-300
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which THREE factors should you consider when designing a star schema for a Power BI semantic model? (Select three.)
hard- ✓ A.Fact tables should contain measures and foreign keys to dimension tables.
- ✓ B.Dimension tables should contain descriptive attributes and be denormalized.
- C.Fact tables should be normalized to reduce data duplication.
- D.Use calculated columns in dimension tables to derive new attributes.
- ✓ E.Avoid creating many-to-many relationships between dimensions.
Why A: The correct factors are: Fact tables should contain measures and foreign keys to dimension tables (A). Dimension tables should contain descriptive attributes and be denormalized (B). Avoid creating many-to-many relationships between dimensions; instead, use a bridge table when necessary (E). Option C is incorrect because fact tables should not be normalized; they should be denormalized to improve query performance. Option D is incorrect because calculated columns in dimension tables can increase model size and processing time; they are better placed as measures or in the fact table.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PL-300 practice question is part of Courseiva's free Microsoft certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PL-300 exam.