Outline The Need for Databases Data Models Relational Databases Database Design Storage Manager Query Processing Transaction Manager Database System Concepts-6th Edition 1.2 ©Silberschat乜，Korth and Sudarshan
Database System Concepts - 6 1.2 ©Silberschatz, Korth and Sudarshan th Edition Outline The Need for Databases Data Models Relational Databases Database Design Storage Manager Query Processing Transaction Manager
Database Management System (DBMS) DBMS contains information about a particular enterprise Collection of interrelated data Set of programs to access the data An environment that is both convenient and efficient to use Database Applications: Banking:transactions Airlines:reservations,schedules Universities:registration,grades Sales:customers,products,purchases Online retailers:order tracking,customized recommendations Manufacturing:production,inventory,orders,supply chain Human resources:employee records,salaries,tax deductions Databases can be very large. Databases touch all aspects of our lives Database System Concepts-6th Edition 1.3 ©Silberschat乜，Korth and Sudarshan
Database System Concepts - 6 1.3 ©Silberschatz, Korth and Sudarshan th Edition Database Management System (DBMS) DBMS contains information about a particular enterprise Collection of interrelated data Set of programs to access the data An environment that is both convenient and efficient to use Database Applications: Banking: transactions Airlines: reservations, schedules Universities: registration, grades Sales: customers, products, purchases Online retailers: order tracking, customized recommendations Manufacturing: production, inventory, orders, supply chain Human resources: employee records, salaries, tax deductions Databases can be very large. Databases touch all aspects of our lives
University Database Example Application program examples Add new students,instructors,and courses Register students for courses,and generate class rosters Assign grades to students,compute grade point averages (GPA)and generate transcripts In the early days,database applications were built directly on top of file systems Database System Concepts-6th Edition 1.4 @Silberschatz,Korth and Sudarshan
Database System Concepts - 6 1.4 ©Silberschatz, Korth and Sudarshan th Edition University Database Example Application program examples Add new students, instructors, and courses Register students for courses, and generate class rosters Assign grades to students, compute grade point averages (GPA) and generate transcripts 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-6th Edition 1.5 @Silberschatz,Korth and Sudarshan
Database System Concepts - 6 1.5 ©Silberschatz, Korth and Sudarshan th Edition 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
Drawbacks of using file systems to store data (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 Example: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-6th Edition 1.6 ©Silberschat乜，Korth and Sudarshan
Database System Concepts - 6 1.6 ©Silberschatz, Korth and Sudarshan th Edition Drawbacks of using file systems to store data (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 Example: 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