1.data base testing is also called as back end end testing.we conduct this testing based on data validation and data integrity.data validation means that whether front end values are correctly storing into back tables content or not.data integrity means that whether impact of front end operations.

2.web server:A web server is a computer which serves HTML pages to the clients requests i.e web browsers .

3.in product based company there is  no question of testing the product in development stage .the complete product would be developed and would be given for QA team for testing.so first comes the stage of development and then when te product is complete then testing and when all the requirements are achieved then the product would be given to the delivery team for release.