Chapter 1: Introduction Database Management System (DBMS)
■ Collection of interrelated data
■ Purpose of Database Systems ■ Set of programs to access the data
■ View of Data ■ DBMS contains information about a particular enterprise
■ Data Models ■ DBMS provides an environment that is both convenient and
efficient to use.
■ Data Definition Language
■ Database Applications:
■ Data Manipulation Language
★ Banking: all transactions
■ Transaction Management ★ Airlines: reservations, schedules
■ Storage Management ★ Universities: registration, grades
■ Database Administrator ★ Sales: customers, products, purchases
★ Manufacturing: production, inventory, orders, supply chain
■ Database Users
★ Human resources: employee records, salaries, tax deductions
■ Overall System Structure
■ Databases touch all aspects of our lives
Database System Concepts 1.1 ©Silberschatz, Korth and Sudarshan Database System Concepts 1.2 ©Silberschatz, Korth and Sudarshan
Purpose of Database System Purpose of Database Systems (Cont.)
■ Drawbacks of using file systems (cont.)
■ In the early days, database applications were built on top of
file systems ★ Atomicity of updates
✔ Failures may leave database in an inconsistent state with partial
■ Drawbacks of using file systems to store data:
updates carried out
★ Data redundancy and inconsistency
✔ E.g. transfer of funds from one account to another should either
✔ Multiple file formats, duplication of information in different files complete or not happen at all
★ Difficulty in accessing data ★ Concurrent access by multiple users
✔ Need to write a new program to carry out each new task ✔ Concurrent accessed needed for performance
★ Data isolation — multiple files and formats ✔ Uncontrolled concurrent accesses can lead to inconsistencies
★ Integrity problems – E.g. two people reading a balance and updating it at the same
✔ Integrity constraints (e.g. account balance > 0) become part time
of program code ★ Security problems
✔ Hard to add new constraints or change existing ones ■ Database systems offer solutions to all the above problems
Database System Concepts 1.3 ©Silberschatz, Korth and Sudarshan Database System Concepts 1.4 ©Silberschatz, Korth and Sudarshan
Levels of Abstraction View of Data
An architecture for a database system
■ 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 1.5 ©Silberschatz, Korth and Sudarshan Database System Concepts 1.6 ©Silberschatz, Korth and Sudarshan
Instances and Schemas Data Models
■ Similar to types and variables in programming languages
■ Schema – the logical structure of the database
■ A collection of tools for describing
★ e.g., the database consists of information about a set of customers and
★ data
accounts and the relationship between them) ★ data relationships
★ Analogous to type information of a variable in a program ★ data semantics
★ Physical schema: database design at the physical level ★ data constraints
★ Logical schema: database design at the logical level ■ Entity-Relationship model
■ Instance – the actual content of the database at a particular point in time ■ Relational model
★ Analogous to the value of a variable
■ Other models:
■ Physical Data Independence – the ability to modify the physical schema
★ object-oriented model
without changing the logical schema
★ semi-structured data models
★ Applications depend on the logical schema ★ Older models: network model and hierarchical model
★ 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 1.7 ©Silberschatz, Korth and Sudarshan Database System Concepts 1.8 ©Silberschatz, Korth and Sudarshan
■ Collection of interrelated data
■ Purpose of Database Systems ■ Set of programs to access the data
■ View of Data ■ DBMS contains information about a particular enterprise
■ Data Models ■ DBMS provides an environment that is both convenient and
efficient to use.
■ Data Definition Language
■ Database Applications:
■ Data Manipulation Language
★ Banking: all transactions
■ Transaction Management ★ Airlines: reservations, schedules
■ Storage Management ★ Universities: registration, grades
■ Database Administrator ★ Sales: customers, products, purchases
★ Manufacturing: production, inventory, orders, supply chain
■ Database Users
★ Human resources: employee records, salaries, tax deductions
■ Overall System Structure
■ Databases touch all aspects of our lives
Database System Concepts 1.1 ©Silberschatz, Korth and Sudarshan Database System Concepts 1.2 ©Silberschatz, Korth and Sudarshan
Purpose of Database System Purpose of Database Systems (Cont.)
■ Drawbacks of using file systems (cont.)
■ In the early days, database applications were built on top of
file systems ★ Atomicity of updates
✔ Failures may leave database in an inconsistent state with partial
■ Drawbacks of using file systems to store data:
updates carried out
★ Data redundancy and inconsistency
✔ E.g. transfer of funds from one account to another should either
✔ Multiple file formats, duplication of information in different files complete or not happen at all
★ Difficulty in accessing data ★ Concurrent access by multiple users
✔ Need to write a new program to carry out each new task ✔ Concurrent accessed needed for performance
★ Data isolation — multiple files and formats ✔ Uncontrolled concurrent accesses can lead to inconsistencies
★ Integrity problems – E.g. two people reading a balance and updating it at the same
✔ Integrity constraints (e.g. account balance > 0) become part time
of program code ★ Security problems
✔ Hard to add new constraints or change existing ones ■ Database systems offer solutions to all the above problems
Database System Concepts 1.3 ©Silberschatz, Korth and Sudarshan Database System Concepts 1.4 ©Silberschatz, Korth and Sudarshan
Levels of Abstraction View of Data
An architecture for a database system
■ 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 1.5 ©Silberschatz, Korth and Sudarshan Database System Concepts 1.6 ©Silberschatz, Korth and Sudarshan
Instances and Schemas Data Models
■ Similar to types and variables in programming languages
■ Schema – the logical structure of the database
■ A collection of tools for describing
★ e.g., the database consists of information about a set of customers and
★ data
accounts and the relationship between them) ★ data relationships
★ Analogous to type information of a variable in a program ★ data semantics
★ Physical schema: database design at the physical level ★ data constraints
★ Logical schema: database design at the logical level ■ Entity-Relationship model
■ Instance – the actual content of the database at a particular point in time ■ Relational model
★ Analogous to the value of a variable
■ Other models:
■ Physical Data Independence – the ability to modify the physical schema
★ object-oriented model
without changing the logical schema
★ semi-structured data models
★ Applications depend on the logical schema ★ Older models: network model and hierarchical model
★ 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 1.7 ©Silberschatz, Korth and Sudarshan Database System Concepts 1.8 ©Silberschatz, Korth and Sudarshan
