数据库管理系统：ch01 Introduction
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Models an enterprise as a collection of entities and relationships Entity: a “thing” or “object” in the enterprise that is distinguishable from other objects Described by a set of attributes Relationship: an association among several entities
Relational model Entity-Relationship data model (mainly for database design) Object-based data models (Object-oriented and Object-relational) Semistructured data model (XML) Other older models:
Database System Concepts - 5th Edition, May 23, 2005
1.3
©Silberschatz, Korth and Sudarshan
Database Management System (DBMS)
DBMS provides an environment that is both convenient and efficient to use. It contains
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 customer_id : string; customer_name : string; customer_street : string; customer_city : integer;
end; View level: application programs hide details of data types. Views can also hide information (such as an employee’s salary) for security purposes.
Database System Concepts - 5th Edition, May 23, 2005
1.9
©Silberschatz, Korth and Sudarshan
Data Models
A collection of tools for describing Data Data relationships Data semantics Data constraints
Example: 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 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.
An Introduction to Database System
Database System Concepts - 5th Edition, May 23, 2005
1.1
©Silberschatz, Korth and Sudarshan
Chapter 1: Introduction
Database System Concepts, 5th Ed.
Database System Concepts - 5th Edition, May 23, 2005
1.7
©Silberschatz, Korth and Sudarshan
View of Data
An architecture for a database system
Database System Concepts - 5th Edition, May 23, 2005
Database systems offer solutions to all the above problems
Database System Concepts - 5th Edition, May 23, 2005
1.6
©Silberschatz, Korth and Sudarshan
Levels of Abstraction
Hard to add new constraints or change existing ones
ห้องสมุดไป่ตู้
Database System Concepts - 5th Edition, May 23, 2005
1.5
©Silberschatz, Korth and Sudarshan
Purpose of Database Systems (Cont.)
©Silberschatz, Korth and Sudarshan See for conditions on re-use
Chapter 1: Introduction
Database-System Applications Purpose of Database Systems View of Data Database Languages Relational Databases Database Design Object-based and semistructured databases Data Storage and Querying Transaction Management Database Architecture Database Users and Administrators Overall Structure History of Database Systems
1.8
©Silberschatz, Korth and Sudarshan
Instances and Schemas
Similar to types and variables in programming languages Schema – the logical structure of the database
Network model Hierarchical model
Database System Concepts - 5th Edition, May 23, 2005
1.10
©Silberschatz, Korth and Sudarshan
The Entity-Relationship Model
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
Drawbacks of using file 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 accessed needed for performance Uncontrolled concurrent accesses can lead to inconsistencies – Example: Two people reading a balance and updating it at the same time Security problems Hard to provide user access to some, but not all, 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
A collection of interrelated data, i.e. database which contains information about a particular enterprise A set of programs to access the data Database Applications: Banking: all 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 touch all aspects of our lives
Database System Concepts - 5th Edition, May 23, 2005
1.4
©Silberschatz, Korth and Sudarshan
Purpose of Database Systems
In the early days, database applications were built directly on top of file systems Drawbacks of using file systems to store data:
Relational model Entity-Relationship data model (mainly for database design) Object-based data models (Object-oriented and Object-relational) Semistructured data model (XML) Other older models:
Database System Concepts - 5th Edition, May 23, 2005
1.3
©Silberschatz, Korth and Sudarshan
Database Management System (DBMS)
DBMS provides an environment that is both convenient and efficient to use. It contains
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 customer_id : string; customer_name : string; customer_street : string; customer_city : integer;
end; View level: application programs hide details of data types. Views can also hide information (such as an employee’s salary) for security purposes.
Database System Concepts - 5th Edition, May 23, 2005
1.9
©Silberschatz, Korth and Sudarshan
Data Models
A collection of tools for describing Data Data relationships Data semantics Data constraints
Example: 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 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.
An Introduction to Database System
Database System Concepts - 5th Edition, May 23, 2005
1.1
©Silberschatz, Korth and Sudarshan
Chapter 1: Introduction
Database System Concepts, 5th Ed.
Database System Concepts - 5th Edition, May 23, 2005
1.7
©Silberschatz, Korth and Sudarshan
View of Data
An architecture for a database system
Database System Concepts - 5th Edition, May 23, 2005
Database systems offer solutions to all the above problems
Database System Concepts - 5th Edition, May 23, 2005
1.6
©Silberschatz, Korth and Sudarshan
Levels of Abstraction
Hard to add new constraints or change existing ones
ห้องสมุดไป่ตู้
Database System Concepts - 5th Edition, May 23, 2005
1.5
©Silberschatz, Korth and Sudarshan
Purpose of Database Systems (Cont.)
©Silberschatz, Korth and Sudarshan See for conditions on re-use
Chapter 1: Introduction
Database-System Applications Purpose of Database Systems View of Data Database Languages Relational Databases Database Design Object-based and semistructured databases Data Storage and Querying Transaction Management Database Architecture Database Users and Administrators Overall Structure History of Database Systems
1.8
©Silberschatz, Korth and Sudarshan
Instances and Schemas
Similar to types and variables in programming languages Schema – the logical structure of the database
Network model Hierarchical model
Database System Concepts - 5th Edition, May 23, 2005
1.10
©Silberschatz, Korth and Sudarshan
The Entity-Relationship Model
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
Drawbacks of using file 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 accessed needed for performance Uncontrolled concurrent accesses can lead to inconsistencies – Example: Two people reading a balance and updating it at the same time Security problems Hard to provide user access to some, but not all, 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
A collection of interrelated data, i.e. database which contains information about a particular enterprise A set of programs to access the data Database Applications: Banking: all 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 touch all aspects of our lives
Database System Concepts - 5th Edition, May 23, 2005
1.4
©Silberschatz, Korth and Sudarshan
Purpose of Database Systems
In the early days, database applications were built directly on top of file systems Drawbacks of using file systems to store data: