Fact tables contain keys to dimension tables as well as measurable facts that data analysts would want to examine
Dimension tables are used to describe dimensions; they contain dimension keys, values and attributes.
In general dimension tables holds the description / textual information about facts stored in fact tables.
The fact tables contains foreign keys referring to the dimension tables.
With out having /using the dimensions using fact table is meaning less
For ex dimetions..
sales is fact table,product,year are dimensions ..
how can find the sales for a particular year/month with out using the dimension(year )
This is general funda, that you always load dimension tables first and then fact tables. You need to follow this way, no other way would make a real sense as far as in real world!!
Lots of Information is available in Net about Dimensions and Facts. But below is my understanding.
In general, the world is full of objects which have some properties and activities. In most of the cases the properties are static and activities are dynamic.
In Database terms Object can be called as Entity and it will have some attributes (properties). This event will do some transactions (activities or tasks). These transactions may or may not be measurable.
For example a Customer (Entity) can have an Account Number (attribute) and a Name (attribute). This Customer can purchage one Product (Entity) named X (attribute) for the cost $500 (measurable item). The Customer or Production relatetd Attributes information will be stored in Master tables and the transaction related to these master tables will be stored in transactions tables.
In Data Warehousing terms these Customers, Products etc are called as Dimension tables where attribute level information is stored and the transaction level information (non attributes, measurable and non measurable) will be stored in Fact Tables.
But in Database the tables are related using Entity & Relationship Model and in Data Warehousing the Dimensions & Facts are related using Star Schema, Snowflake Schema etc. Each modeling has its own purpose and advantage.
For instance, Cost is the measurable item which will be stored in Fact table and met an accident is non measurable item.
This is my basic idea about demensions and facts.