Purpose of Database Systems (Cont.) Atomicity of updates Failures may leave database in an inconsistent state with partial updates carried out Example:Transfer of funds from one account to another should either complete or not happen at all Concurrent access by multiple users Concurrent access needed for performance Uncontrolled concurrent accesses can lead to inconsistencies Ex:Two people reading a balance (say 100)and updating it by withdrawing money (say 50 each)at the same time Security problems Hard to provide user access to some,but not all,data Database systems offer solutions to all the above problems Database System Concepts-7th Edition 1.7 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 1.7 ©Silberschatz, Korth and Sudarshan th Edition Purpose of Database Systems (Cont.) ▪ Atomicity of updates • Failures may leave database in an inconsistent state with partial updates carried out • Example: Transfer of funds from one account to another should either complete or not happen at all ▪ Concurrent access by multiple users • Concurrent access needed for performance • Uncontrolled concurrent accesses can lead to inconsistencies ▪ Ex: Two people reading a balance (say 100) and updating it by withdrawing money (say 50 each) at the same time ▪ Security problems • Hard to provide user access to some, but not all, data Database systems offer solutions to all the above problems