why Star Schema ? what is Star Schema?

• Poor system performance. A data warehouse usually contains a large volume of data. It is not an easy job to retrieve data quickly from the data warehouse for analysis purpose. 

For this reason, the data warehouse design uses a special technique called a Star Schema.

The Star Schema derives its name from its graphical representation -  that is, it look like a star.

The Fact Table appears in the middle of the graphic, along with several surrounding Dimension Tables.
The central Fact Table is usually very large, measured in gigabytes. It is the table from which we retrieve the interesting data.

The size of the Dimension Tables amounts to only 1 to 5 percent of the size fo the Fact Table. Common dimensions are Unit and Time.

Foreign keys tie the fact table to the dimension tables. 

what is SAP? abbreviation for SAP? History of SAP?

SAP : - Systems Applications and Products in data processing is business software for that can  be customized according to the requirements of a user.

SAP was developed by the SAP AG Company, Germany, where SAP stands for Systeme, Anwendungen und Produkte in der Datenverabeitung. 

The basic idea behind developing SAP was the need to introduce standard application software that helps in real-time business processing.

A standard SAP system is divided in to three systems, namely

• Development 
• Quality Assurance and
• Production 

The development systems helps customized data in a SAP system.

The Quality Assurance Systems performs the final testing before the SAP applications are used in the production system.

The Production system helps perform the day-to-day business activities (Transactional Data).