Lecture 3: Introduction to Dimensionality Flashcards
What is a Dimensional Model?
A data structure technique optimized for data warehousing, designed to make querying and reporting simpler.
Which main elements make up a Dimensional Model?
Facts (measurements) and Dimensions (descriptive attributes surrounding facts).
What is a Fact Table?
A primary table in a dimensional model that contains measurements (facts) and foreign keys to dimension tables.
What is stored in a Fact Table?
Numeric measurements of business processes and foreign key links to dimensions.
What does ‘Granularity’ refer to in a Fact Table?
It defines the level of detail of the data, such as daily transactions vs. monthly or quarterly aggregates.
What is a Surrogate Key?
A system-generated unique identifier with no inherent business meaning.
What is a Natural Key?
An existing business identifier that already uniquely identifies an entity, such as a product code.
What is Cardinality in data relationships?
It describes how many relationships can exist between two entities (e.g., one-to-many or many-to-many).
Give an example of Cardinality in a data warehouse.
A single customer (one) can have multiple sales transactions (many), forming a one-to-many relationship.
What are Dimensions?
They provide context and descriptive characteristics of the facts (e.g., who, what, where).
What are Attributes in a Dimension?
Descriptive details of a dimension that help filter or classify data, such as region or product category.
Provide an example of a Fact in retail.
‘Total sales amount’ or ‘number of items sold’ are typical facts.
Provide an example of a Dimension in retail.
‘Customer’ dimension, with attributes like name, location, and loyalty level.
Why do we use Dimensional Models in data warehousing?
To optimize query performance and simplify data analysis by separating numeric facts from descriptive dimensions.
