Database A database consists of multiple relations Information about an enterprise is broken up into parts,with each relation storing one part of the information account:stores information about accounts deposifor:stores information about which customer owns which account customer:stores information about customers Storing all information as a single relation such as bank(account number,balance,customer_name,..) results in repetition of information e.g.,if two customers own an account(What gets repeated?) the need for null values e.g.,to represent a customer without an account Normalization theory(Chapter 7)deals with how to design relational schemas Database System Concepts -5th Edition,Oct 5,2006 2.9 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 5 2.9 ©Silberschatz, Korth and Sudarshan th Edition, Oct 5, 2006 Database A database consists of multiple relations Information about an enterprise is broken up into parts, with each relation storing one part of the information account : stores information about accounts depositor : stores information about which customer owns which account customer : stores information about customers Storing all information as a single relation such as bank(account_number, balance, customer_name, ..) results in repetition of information  e.g.,if two customers own an account (What gets repeated?) the need for null values  e.g., to represent a customer without an account Normalization theory (Chapter 7) deals with how to design relational schemas