DATABASE SYSTEM CONCEPTS instructor: Jingsheng Lei(雷景生) E-mail: ishleiahainu. edu. cn 标 Database System Concepts 1.1 @Silberschatz, Korth and Sudarshan
Database System Concepts 1.1 ©Silberschatz, Korth and Sudarshan DATABASE SYSTEM CONCEPTS instructor: Jingsheng Lei(雷景生) E-mail: jshlei@hainu.edu.cn
Chapter 1: Introduction Applications of Database Systems Database Systems versus File Systems View of data Data Models Database Language Database Users and administrator Transaction Management Database System Structure Application Architectures History of Database Systems Summary 标 Database System Concepts @Silberschatz, Korth and Sudarshan
Database System Concepts 1.2 ©Silberschatz, Korth and Sudarshan Chapter 1: Introduction Applications of Database Systems Database Systems versus File Systems View of Data Data Models Database Language Database Users and Administrator Transaction Management Database System Structure Application Architectures History of Database Systems Summary
Database Management System(DBMS) Collection of interrelated data Set of programs to access the data DB contains information about a particular enterprise DBMS provides an environment that is both convenient and efficient to use Database systems are designed to manage large bodies of information DBS must ensure the safety of the information stored Several users Data Database(DB) Database Management System (DBMS) Database System(DBS) Database System Concepts 1.3 OSilberschatz. Korth and Sudarshan
Database System Concepts 1.3 ©Silberschatz, Korth and Sudarshan Database Management System (DBMS) Collection of interrelated data. Set of programs to access the data. DB contains information about a particular enterprise. DBMS provides an environment that is both convenient and efficient to use. Database systems are designed to manage large bodies of information. DBS must ensure the safety of the information stored. Several users. Data Database(DB) Database Management System (DBMS) Database System(DBS)
1 Applications of Database Systems Database Applications: Banking: all transactions Airlines: reservations, schedules Universities: registration, grades Sales: customers, products, purchases Manufacturing: production, inventory, orders, supply chain Human resources: employee records, salaries, tax deductions Databases touch all aspects of our lives Database System Concepts 1.4 OSilberschatz. Korth and Sudarshan
Database System Concepts 1.4 ©Silberschatz, Korth and Sudarshan 1 Applications of Database Systems Database Applications: Banking: all transactions Airlines: reservations, schedules Universities: registration, grades Sales: customers, products, purchases Manufacturing: production, inventory, orders, supply chain Human resources: employee records, salaries, tax deductions Databases touch all aspects of our lives
2 Database Systems versus File Systems In the early days, database applications were built 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 part of program code Hard to add new constraints or change existing ones Database System Concepts 1.5 OSilberschatz. Korth and Sudarshan
Database System Concepts 1.5 ©Silberschatz, Korth and Sudarshan 2 Database Systems versus File Systems In the early days, database applications were built 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 part of program code Hard to add new constraints or change existing ones
2 Database Systems versus File Systems(Cont) Drawbacks of using file systems(cont) Atomicity of updates Failures may leave database in an inconsistent state with partial updates carried out E.g. transfer of funds from one account to another should either complete or not happen at all Concurrent access by multiple users Concurrent accessed needed for performance Uncontrolled concurrent accesses can lead to inconsistencies E.g. two people reading a balance and updating it at the same time 标 Security problems Database System Concepts 1.6 @Silberschatz, Korth and Sudarshan
Database System Concepts 1.6 ©Silberschatz, Korth and Sudarshan 2 Database Systems versus File Systems(Cont.) Drawbacks of using file systems (cont.) Atomicity of updates Failures may leave database in an inconsistent state with partial updates carried out E.g. transfer of funds from one account to another should either complete or not happen at all Concurrent access by multiple users Concurrent accessed needed for performance Uncontrolled concurrent accesses can lead to inconsistencies – E.g. two people reading a balance and updating it at the same time Security problems
3 View of Data 3.1 Data Abstraction Physical level describes how a record(e.g customer)is stored Logical level: describes data stored in database, and the relationships among the data type customer record name: string; street: string city: integer; end View level; application programs hide details of data types. Views can also hide information(e.g, salary) for security purposes Database System Concepts 1.7 @Silberschatz, Korth and Sudarshan
Database System Concepts 1.7 ©Silberschatz, Korth and Sudarshan 3 View of Data 3.1 Data Abstraction Physical level describes how a record (e.g., customer) is stored. Logical level: describes data stored in database, and the relationships among the data. type customer = record name : string; street : string; city : integer; end; View level: application programs hide details of data types. Views can also hide information (e.g., salary) for security purposes
3 View of Data(Cont) An architecture for a database system view level view 2 view n 81c level level Database System Concepts 1.8 OSilberschatz. Korth and Sudarshan
Database System Concepts 1.8 ©Silberschatz, Korth and Sudarshan 3 View of Data (Cont.) An architecture for a database system
3 View of Data(Cont) 3.2 Instances and schemas Similar to types and variables in programming languages Schema -the logical structure of the database e.g., the database consists of information about a set of customers and accounts and the relationship between them) Analogous to type information of a variable in a program Physical schema: database design at the physical level Logical schema: database design at the logical level Database System Concepts 1.9 @Silberschatz, Korth and Sudarshan
Database System Concepts 1.9 ©Silberschatz, Korth and Sudarshan 3 View of Data (Cont.) 3.2 Instances and Schemas Similar to types and variables in programming languages Schema – the logical structure of the database e.g., the database consists of information about a set of customers and accounts and the relationship between them) Analogous to type information of a variable in a program Physical schema: database design at the physical level Logical schema: database design at the logical level
3 View of Data(Cont) Instance- the actual content of the database at a particular point in time Analogous to the value of a variable Physical Data Independence- the ability to modify the physical schema without changing the logical schema Applications depend on the logical schema In general, the interfaces between the various levels and components should be well defined so that changes in some parts do not seriously influence others Database System Concepts 1.10 OSilberschatz. Korth and Sudarshan
Database System Concepts 1.10 ©Silberschatz, Korth and Sudarshan 3 View of Data (Cont.) Instance – the actual content of the database at a particular point in time Analogous to the value of a variable Physical Data Independence – the ability to modify the physical schema without changing the logical schema Applications depend on the logical schema In general, the interfaces between the various levels and components should be well defined so that changes in some parts do not seriously influence others