Purpose of Database Systems In the early days,database applications were built directly on top of file systems,which leads to: Data redundancy and inconsistency:data is stored in multiple file formats resulting induplication 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-7th Edition 1.6 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 1.6 ©Silberschatz, Korth and Sudarshan th Edition Purpose of Database Systems ▪ Data redundancy and inconsistency: data is stored in multiple file formats resulting induplication 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 In the early days, database applications were built directly on top of file systems, which leads to: