PL-300 Model the data Practice Question
You are a data analyst for a healthcare provider. You have a Power BI semantic model with a fact table named Encounters and a dimension table named Patients. The Patients table contains a column PatientKey and a column MRN (medical record number). Some patients have multiple MRNs because they were registered at different clinics. You need to create a relationship between Encounters and Patients that ensures each encounter is attributed to exactly one patient record. What should you do?
⚠ Common exam trap
The trap here is assuming that the natural business identifier (MRN) should be used for the relationship instead of the surrogate key that actually links the 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
✓
Create a one-to-many relationship from Patients[PatientKey] to Encounters[PatientKey].
The Patients dimension has a unique PatientKey that is referenced by the Encounters fact table. Creating a one-to-many relationship from Patients[PatientKey] to Encounters[PatientKey] enforces referential integrity and ensures each encounter maps to exactly one patient row. Using MRN would be incorrect because it is not unique and is not present in the fact table.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Create a one-to-many relationship from Patients[PatientKey] to Encounters[PatientKey].
Why this is correct
This is correct because PatientKey is the unique surrogate key in the Patients dimension and Encounters[PatientKey] is the foreign key. A one-to-many relationship from the dimension to the fact table enforces that each encounter relates to exactly one patient record, regardless of how many MRNs that patient has.
- ✗
Create a many-to-many relationship between Patients[MRN] and Encounters[PatientKey].
Why it's wrong here
This fails because Encounters[PatientKey] does not contain MRN values, so the relationship would not match related records. Even if it did, many-to-many on MRN would allow an encounter to relate to multiple patient rows, which violates the requirement that each encounter be attributed to exactly one patient record.
- ✗
Create a bidirectional many-to-many relationship between Patients[MRN] and Encounters[MRN].
Why it's wrong here
This fails because Encounters does not have an MRN column, and even if it did, a bidirectional many-to-many relationship would not guarantee a single patient record per encounter. It would also introduce ambiguity and potential circular filtering, which is not appropriate for this attribution requirement.
- ✗
Create a one-to-many relationship from Patients[MRN] to Encounters[PatientKey].
Why it's wrong here
This is wrong because MRN is not the column used in the Encounters table; Encounters contains PatientKey. A relationship between mismatched columns will not resolve correctly, and MRN is not unique per patient here, so it cannot reliably serve as the dimension side of a one-to-many relationship.
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Last reviewed September 2026 · checked against the official Microsoft exam blueprint
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