Chapter 3: Data Modeling & Relationships in Power BI

 Data Modeling in Power BI: Tables, Keys, Relationships

What is Data Modeling in Power BI?

Data Modeling in Power BI is the process of organizing multiple datasets and creating relationships between them so that data can be analyzed accurately and efficiently.

In real-world business scenarios, data does not exist in a single table. Instead, it is distributed across multiple tables such as Sales, Customers, Products, and Date tables.

Why Data Modeling is Important

Proper data modeling ensures that Power BI produces correct calculations, improves report performance, and enables advanced DAX formulas.

Benefit	Explanation
Accurate Calculations	Ensures totals and measures are correct
Better Performance	Optimized models load faster

What is a Relationship?

A relationship is a logical connection between two tables using a common column. This allows Power BI to understand how data from different tables is related.

Example

Sales[CustomerID] connected with Customers[CustomerID]

Types of Relationships in Power BI

Relationship Type	Description
One-to-Many (1:*)	One record relates to many records (most common)
Many-to-One (*:1)	Multiple records connect to one record
One-to-One (1:1)	Each record matches exactly one record
Many-to-Many (*:*)	Multiple records connect on both sides

Primary Key and Foreign Key

A Primary Key uniquely identifies each record in a table, while a Foreign Key references the primary key of another table to create a relationship.

How to Create Relationships

Relationships can be created automatically by Power BI or manually using Model View or the Manage Relationships option.

Cross Filter Direction

Cross filter direction defines how filters move between related tables. Single direction is recommended for better performance, while both direction is used in complex scenarios.

Star Schema (Best Practice)

Star schema is a widely used data modeling approach where a central fact table is connected to multiple dimension tables.

Fact Table vs Dimension Table

Fact Table	Dimension Table
Contains numeric data	Contains descriptive data
Used for calculations	Used for filtering

Best Practices

Always use one-to-many relationships, follow star schema design, ensure correct data types, and avoid unnecessary many-to-many relationships.

Chapter Summary

Chapter 5 builds the foundation for advanced Power BI concepts. A strong data model ensures accurate analysis and prepares students for DAX calculations.