Data base management systems ppt

©Silberschatz, Korth and Sudarshan1.1Database System Concepts
Chapter 1: IntroductionChapter 1: Introduction
s Purpose of Database Systems
s View of Data
s Data Models
s Data Definition Language
s Data Manipulation Language
s Transaction Management
s Storage Management
s Database Administrator
s Database Users
s Overall System Structure
Database Management System (DBMS)Database Management System (DBMS)
s Collection of interrelated data
s Set of programs to access the data
s DBMS contains information about a particular enterprise
s DBMS provides an environment that is both convenient and
efficient to use.
s Database Applications:
5 Banking: all transactions
5 Airlines: reservations, schedules
5 Universities: registration, grades
5 Sales: customers, products, purchases
5 Manufacturing: production, inventory, orders, supply chain
5 Human resources: employee records, salaries, tax deductions
s Databases touch all aspects of our lives
Purpose of Database SystemPurpose of Database System
s In the early days, database applications were built on top of
file systems
s Drawbacks of using file systems to store data:
5 Data redundancy and inconsistency
Multiple file formats, duplication of information in different files
5 Difficulty in accessing data
Need to write a new program to carry out each new task
5 Data isolation — multiple files and formats
5 Integrity problems
Integrity constraints (e.g. account balance > 0) become part
of program code
Hard to add new constraints or change existing ones
Purpose of Database Systems (Cont.)Purpose of Database Systems (Cont.)
s Drawbacks of using file systems (cont.)
5 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
5 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
5 Security problems
s Database systems offer solutions to all the above problems
Levels of AbstractionLevels of Abstraction
s Physical level describes how a record (e.g., customer) is stored.
s Logical level: describes data stored in database, and the
relationships among the data.
type customer = record
name : string;
street : string;
city : integer;
end;
s View level: application programs hide details of data types.
Views can also hide information (e.g., salary) for security
purposes.
View of DataView of Data
An architecture for a database system
Instances and SchemasInstances and Schemas
s Similar to types and variables in programming languages
s Schema – the logical structure of the database
5 e.g., the database consists of information about a set of customers and
accounts and the relationship between them)
5 Analogous to type information of a variable in a program
5 Physical schema: database design at the physical level
5 Logical schema: database design at the logical level
s Instance – the actual content of the database at a particular point in time
5 Analogous to the value of a variable
s Physical Data Independence – the ability to modify the physical schema
without changing the logical schema
5 Applications depend on the logical schema
5 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.
Data ModelsData Models
s A collection of tools for describing
5 data
5 data relationships
5 data semantics
5 data constraints
s Entity-Relationship model
s Relational model
s Other models:
5 object-oriented model
5 semi-structured data models
5 Older models: network model and hierarchical model

Entity-Relationship ModelEntity-Relationship Model
Example of schema in the entity-relationship model
Entity Relationship Model (Cont.)Entity Relationship Model (Cont.)
s E-R model of real world
5 Entities (objects)
E.g. customers, accounts, bank branch
5 Relationships between entities
E.g. Account A-101 is held by customer Johnson
Relationship set depositor associates customers with accounts
s Widely used for database design
5 Database design in E-R model usually converted to design in the
relational model (coming up next) which is used for storage and
processing
Relational ModelRelational Model
s Example of tabular data in the relational model
customer-
name
Customer-
id
customer-
street
customer-
city
account-
number
Johnson
Smith
Johnson
Jones
Smith
192-83-7465
019-28-3746
192-83-7465
321-12-3123
019-28-3746
Alma
North
Alma
Main
North
Palo Alto
Rye
Palo Alto
Harrison
Rye
A-101
A-215
A-201
A-217
A-201
Attributes
A Sample Relational DatabaseA Sample Relational Database
Data Definition Language (DDL)Data Definition Language (DDL)
s Specification notation for defining the database schema
5 E.g.
create table account (
account-number char(10),
balance integer)
s DDL compiler generates a set of tables stored in a data
dictionary
s Data dictionary contains metadata (i.e., data about data)
5 database schema
5 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
Data Manipulation Language (DML)Data Manipulation Language (DML)
s Language for accessing and manipulating the data organized by
the appropriate data model
5 DML also known as query language
s Two classes of languages
5 Procedural – user specifies what data is required and how to get
those data
5 Nonprocedural – user specifies what data is required without
specifying how to get those data
s SQL is the most widely used query language
SQLSQL
s SQL: widely used non-procedural language
5 E.g. find the name of the customer with customer-id 192-83-7465
select customer.customer-name
from customer
where customer.customer-id = ‘192-83-7465’
5 E.g. find the balances of all accounts held by the customer with
customer-id 192-83-7465
select account.balance
from depositor, account
where depositor.customer-id = ‘192-83-7465’ and
depositor.account-number = account.account-number
s Application programs generally access databases through one of
5 Language extensions to allow embedded SQL
5 Application program interface (e.g. ODBC/JDBC) which allow SQL
queries to be sent to a database
Database UsersDatabase Users
s Users are differentiated by the way they expect to interact with
the system
s Application programmers – interact with system through DML
calls
s Sophisticated users – form requests in a database query
language
s Specialized users – write specialized database applications that
do not fit into the traditional data processing framework
s Naïve users – invoke one of the permanent application programs
that have been written previously
5 E.g. people accessing database over the web, bank tellers, clerical
staff

Database AdministratorDatabase Administrator
s Coordinates all the activities of the database system; the
database administrator has a good understanding of the
enterprise’s information resources and needs.
s Database administrator's duties include:
5 Schema definition
5 Storage structure and access method definition
5 Schema and physical organization modification
5 Granting user authority to access the database
5 Specifying integrity constraints
5 Acting as liaison with users
5 Monitoring performance and responding to changes in
requirements
Transaction ManagementTransaction Management
s A transaction is a collection of operations that performs a single
logical function in a database application
s Transaction-management component ensures that the database
remains in a consistent (correct) state despite system failures
(e.g., power failures and operating system crashes) and
transaction failures.
s Concurrency-control manager controls the interaction among the
concurrent transactions, to ensure the consistency of the
database.
Storage ManagementStorage Management
s 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.
s The storage manager is responsible to the following tasks:
5 interaction with the file manager
5 efficient storing, retrieving and updating of data
Overall System StructureOverall System Structure
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”

Data base management systems ppt

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Data base management systems ppt