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Database System Concepts 1.1 ©Silberschatz, Korth and Sudarshan
Chapter 1: IntroductionChapter 1: Introduction
Purpose of Database Systems
View of Data
Data Models
Data Definition Language
Data Manipulation Language
Transaction Management
Storage Management
Database Administrator
Database Users
Overall System Structure
Database System Concepts 1.2 ©Silberschatz, Korth and Sudarshan
Database Management System (DBMS)Database Management System (DBMS)
Collection of interrelated data
Set of programs to access the data
DBMS contains information about a particular enterprise
DBMS provides an environment that is both convenient and
efficient to use.
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 1.3 ©Silberschatz, Korth and Sudarshan
Purpose of Database SystemPurpose of Database System
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 1.4 ©Silberschatz, Korth and Sudarshan
Purpose of Database Systems (Cont.)Purpose of Database 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
Database systems offer solutions to all the above problems
Database System Concepts 1.7 ©Silberschatz, Korth and Sudarshan
Instances and SchemasInstances 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 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 1.8 ©Silberschatz, Korth and Sudarshan
Data ModelsData Models
A collection of tools for describing
data data relationships data semantics data constraints
Entity-Relationship model
Relational model
Other models:
object-oriented model semi-structured data models Older models: network model and hierarchical model
Database System Concepts 1.9 ©Silberschatz, Korth and Sudarshan
Entity-Relationship ModelEntity-Relationship Model
Example of schema in the entity-relationship model
Database System Concepts 1.10 ©Silberschatz, Korth and Sudarshan
Entity Relationship Model (Cont.)Entity Relationship Model (Cont.)
E-R model of real world
Entities (objects) ✔ E.g. customers, accounts, bank branch Relationships between entities ✔ E.g. Account A-101 is held by customer Johnson ✔ Relationship set depositor associates customers with accounts
Widely used for database design
Database design in E-R model usually converted to design in the relational model (coming up next) which is used for storage and processing
Database System Concepts 1.13 ©Silberschatz, Korth and Sudarshan
Data Definition Language (DDL)Data Definition Language (DDL)
Specification notation for defining the database schema
E.g. create table account ( account-number char (10), balance integer )
DDL compiler generates a set of tables stored in a data
dictionary
Data dictionary contains metadata (i.e., data about data)
database schema Data storage and definition language ✔ language in which the storage structure and access methods used by the database system are specified ✔ Usually an extension of the data definition language
Database System Concepts 1.14 ©Silberschatz, Korth and Sudarshan
Data Manipulation Language (DML)Data Manipulation Language (DML)
Language for accessing and manipulating the data organized by
the appropriate data model
DML also known as query language
Two classes of languages
Procedural – user specifies what data is required and how to get those data Nonprocedural – user specifies what data is required without specifying how to get those data
SQL is the most widely used query language
Database System Concepts 1.15 ©Silberschatz, Korth and Sudarshan
SQLSQL
SQL: widely used non-procedural language
E.g. find the name of the customer with customer-id 192-83- select customer.customer-name from customer where customer.customer-id = ‘192-83-7465’ E.g. find the balances of all accounts held by the customer with customer-id 192-83- select account.balance from depositor , account where depositor.customer-id = ‘192-83-7465’ and depositor.account-number = account.account-number
Application programs generally access databases through one of
Language extensions to allow embedded SQL Application program interface (e.g. ODBC/JDBC) which allow SQL queries to be sent to a database
Database System Concepts 1.16 ©Silberschatz, Korth and Sudarshan
Database UsersDatabase Users
Users are differentiated by the way they expect to interact with
the system
Application programmers – interact with system through DML
calls
Sophisticated users – form requests in a database query
language
Specialized users – write specialized database applications that
do not fit into the traditional data processing framework
Naïve users – invoke one of the permanent application programs
that have been written previously
E.g. people accessing database over the web, bank tellers, clerical staff
Database System Concepts 1.19 ©Silberschatz, Korth and Sudarshan
Storage ManagementStorage Management
Storage manager is a program module that provides the
interface between the low-level data stored in the database and
the application programs and queries submitted to the system.
The storage manager is responsible to the following tasks:
interaction with the file manager efficient storing, retrieving and updating of data
Database System Concepts 1.20 ©Silberschatz, Korth and Sudarshan
Overall System StructureOverall System Structure
Database System Concepts 1.21 ©Silberschatz, Korth and Sudarshan
Application ArchitecturesApplication Architectures
§ Two-tier architecture : E.g. client programs using ODBC/JDBC to communicate with a database § Three-tier architecture : E.g. web-based applications, and applications built using “middleware”
