🧠 Second Brain

Search

Search IconIcon to open search

Cardinality

Last updated Apr 7, 2024

In the realm of data models, cardinality plays a pivotal role, referring to the uniqueness of data values within a specific column of a database table.

# Example

Cardinality is crucial in managing the vast array of potential combinations in data.

Consider we’re crafting dimensions in a dimensional model. Each dimension bears its own columns and distinct cardinality, denoting a unique count of values. Envision three dimensions in a model; time with 12 values (months), location with ten values (various stores), and product category with five values.

The total combinatorial possibility with these dimensions is their cardinalities’ product. It would calculate to 12 (time) × 10 (location) × 5 (product category) = 600 possible combinations. The complexity escalates with the addition of multiple columns and numerous dimensions. To illustrate, we initially had 12 × 10 = 120 combinations. With the inclusion of the product category, we witness a surge to 480 additional combinations.

Herein lies the limitation of a traditional OLAP cube; the bottleneck being the impractical pre-calculation time that extends beyond reasonable limits (e.g., overnight).

Integrating Many-to-Many Relationships further amplifies this complexity. A measure might relate to a dimension via other Bridge Tables, expanding the potential combination spectrum. The growth trajectory is inherently tied to the specific design and cardinality of the cube’s dimensions and measures.

# Difference to Granularity

Granularity, in contrast, pertains to the precision or depth in a dataset, particularly in a Fact Table within a Dimensional Model (like within a data warehouse). It delineates what each dataset or database table record signifies.

The primary distinction between cardinality and granularity lies in their focal points:

Check more on Big-O, and Granularity


Origin:
References: Granularity
Created 2023-12-19