Before you create a dimensional model, you should understand
the basic objects that you use to create dimensional models: fact
tables and entities, dimension tables and entities, hierarchies, outriggers,
and measures.
Fact tables and entities
A fact table or a fact entity is a table or entity in a star or snowflake schema that stores measures
that measure the business, such as sales, cost of goods, or profit.
Dimension tables and entities
A dimension table or dimension entity is a table or entity in a star, snowflake, or starflake schema that
stores details about the facts. For example, a Time dimension table
stores the various aspects of time such as year, quarter, month, and
day.
Hierarchies
A hierarchy is a many-to-one relationship
between members of a table or between tables. A hierarchy basically
consists of different levels, each corresponding to a dimension attribute.
Outriggers
An outrigger is a dimension table or entity
that is joined to other dimension tables in a star schema. Outriggers
are used when a dimension table is snowflaked.
Measures
Measures define a measurement attribute and
are used in fact tables. You can calculate measures by mapping them
directly to a numerical value in a column or attribute. An aggregation
function summarizes the value of the measure for dimensional analysis.