Purpose of Database Systems In the early days,database applications were built directly on top of file systems Drawbacks of using file systems to store data: Data redundancy and inconsistency Multiple file formats,duplication of information in different files Difficulty in accessing data Need to write a new program to carry out each new task Data isolation-multiple files and formats Integrity problems Integrity constraints (e.g.account balance 0)become "buried"in program code rather than being stated explicitly Hard to add new constraints or change existing ones Database System Concepts-5th Edition,May 23,2005 1.4 @Silberschatz,Korth and SudarshanDatabase System Concepts - 5 1.4 ©Silberschatz, Korth and Sudarshan th Edition, May 23, 2005 Purpose of Database Systems In the early days, database applications were built directly on top of file systems Drawbacks of using file systems to store data: Data redundancy and inconsistency  Multiple file formats, duplication of information in different files Difficulty in accessing data  Need to write a new program to carry out each new task Data isolation — multiple files and formats Integrity problems  Integrity constraints (e.g. account balance > 0) become “buried” in program code rather than being stated explicitly  Hard to add new constraints or change existing ones