Dimension and Facts

Dimensions are categories by which summarized data can be viewed. E.g. a profit summary in a fact table can be viewed by a Time dimension (profit by month, quarter, year), Region dimension
(profit by country, state, city), Product dimension (profit for product1,
product2).

A fact table is a table that contains summarized numerical and historical data
(facts) and a multipart index composed of foreign keys from the primary keys of
related dimension tables.

In data warehousing, a dimension is a collection of reference information about
a measurable event. These events are known as facts and are stored in a fact
table. Dimensions categorize and describe data warehouse facts and measures in
ways that support meaningful answers to business questions. They form the very
core of dimensional modeling.

Dimension tables are referenced by fact tables using keys. When creating a
dimension table in a data warehouse, a system-generated key is used to uniquely
identify a row in the dimension. This key is also known as a surrogate key. The
surrogate key is used as the primary key in the dimension table. The surrogate
key is placed in the fact table and a foreign key is defined between the two
tables. When the data is joined, it does so just as any other join within the
database.