DataBaseManagement System

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Dr.S.Sivakumar,Principal

C.P.A College, Bodinayakanur

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Chapter 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 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

Purpose of Database System

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• 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

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

Levels of 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.

View of Data

An architecture for a database system

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
• 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.

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Data 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

Entity-Relationship Model

Example of schema in the entity-relationship model

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

Relational Model

• Example of tabular data in the relational model

customer-

name

Customer-id

customer-

street

customer-

city

account-

number

Johnson

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Smith

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Johnson

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Jones

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Smith

192-83-7465

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019-28-3746

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192-83-7465

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321-12-3123

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019-28-3746

Alma

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North

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Alma

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Main

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North

Palo Alto

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Rye

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Palo Alto

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Harrison

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Rye

A-101

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A-215

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A-201

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A-217

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A-201

Attributes

A Sample Relational Database

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

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

SQL

• SQL: widely used non-procedural language
• 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’
• 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
• 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

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Database 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 Administrator

• Coordinates all the activities of the database system; the database administrator has a good understanding of the enterprise’s information resources and needs.
• Database administrator's duties include:
• Schema definition
• Storage structure and access method definition
• Schema and physical organization modification
• Granting user authority to access the database
• Specifying integrity constraints
• Acting as liaison with users
• Monitoring performance and responding to changes in requirements

Transaction Management

• A transaction is a collection of operations that performs a single logical function in a database application
• 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.
• Concurrency-control manager controls the interaction among the concurrent transactions, to ensure the consistency of the database.

Storage 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

Overall System Structure

Application 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”