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Introduction to Database Systems

Purpose of Database Systems Views of Data Data Models Data Definition Language Data Manipulation Language Transaction Management Storage Management Database Administrator Database Users Overall System Structure

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Database Management System (DBMS)

Collection of interrelated dataSet of programs to access the dataDBMS contains information about a

particular enterpriseDBMS provides an environment that

is both convenient and efficient to use.

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Purpose of Database Systems

Difficulties in conventional file-processing systems: (DBMS attempts to solve) Data redundancy and inconsistency Difficulty in accessing data Data isolation -- multiple files and formats Integrity problems Atomicity of updates Concurrent access by multiple users Security problems

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View of Data

…...

View level

View 1 View 2 View n

Logical level

Physical level

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Levels of Abstraction

Physical level: describes how a record (eg.: customer) is stored in terms of block#, sector#, byte# etc.

Logical level: describes data stored in database, and the relationship among the data:

customer { string name; string street; integer city; } View level: Application programs/GUI etc hide the actual

representation and present only the required data in a convenient way. Eg: Visual forms, graphical forms.

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Instances and Schemas

Schema is a description and an instance is a set of data that fits the description.

Schema : logical structure of the database (eg. Set of customers and accounts and the relationship between them)

Instance : actual content of the database at a particular point in time.

One schema may have many instances.Analogy : type and variable in a programming

language.

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Data Independence

Ability to modify a schema definition in one level without affecting a scheme definition in the next higher level.

Interfaces between the various levels and components should be well defined so that changes in some parts do not seriously influence others:

Two levels of data independence: Physical data independence Logical data independence

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Data Models A collection of representations for describing:

data, data relationships, data semantics, data constraints Object-based logical models

Entity-Relationship (ER) model Object-oriented model Semantic model Functional model

Record-based logical models Relational model (e.g. SQL/DS, DB2) Network model Hierarchical Model Object relational model

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Entity-Relationship Model

customer

name

SSN street

city

account

number balance

depositor

entity

attribute

relationship

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Relational Model

Name SSN street city account no.

Johnson 192-83-7465 Alma Palo Alto A-101

Customer Table

Account No. Balance

Account Table

A-101 500

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Data Definition Language (DDL)

Specification notation for defining database scheme

DDL compiler generates a set of tables in a data dictionary

Data dictionary contains metadata (data about data)

Data storage and definition language - special type of DDL in which storage and access methods used by the dbms are specified.

SQL create, define tables

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Data Manipulation LanguageLanguage for accessing and manipulating

the data organized by appropriate data model

Two classes of languages: Procedural - user specifies what data is required

and how to get those data Non-procedural -- user specifies what data is

required without specifying how to get those dataQuery language (sequential query language:

sql) : insert data, update data

Relational Algebra

Tables representing relationsRow uniquely identified by a primary keyRelated tables are associated using

foreign keysSpecial operators are defined and

axioms: join, project etc.: relational algebra

http://db.grussell.org/section010.html

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Transaction Management

A transaction is a collection of operations that perform a single logical function in a database application

Example: Withdraw $100 from Acct Number A-101 Verify the balance Update account table (& other tables) Deliver money

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Transaction Management (contd.)

Transaction-management component ensures that the db remains in a correct state despite system failures (e.g. power failures and operating system crashes) and transaction failures.

ACID property: Atomicity, Consistency, Isolation, Durability

Concurrency-control manager controls the interaction among the concurrent transactions.

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Storage Management

A storage manager provides the interface between the low-level data and the application programs and queries submitted to the system.

The storage manager is responsible for the following tasks: interaction with file-manager efficient storing, retrieving, and updating of

data

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Overall System ModelNaïve users Application

programmersSophisticatedusers

DBA

Applicationinterfaces

Application programs

query Database scheme

Qu

ery

pro

cess

ing

DBMS System

Object codeEmbeddedDML compiler

DML compiler

DDL interpreter

Query evaluationengine

Sto

rage

man

ager

Transactionmanager

Buffer manager

File manager

Data dictionaryStatistical dataindicesData files

Disk storage

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Database Administrator

Coordinates all the activities of the database system; DBA should have a good understanding of the

enterprise’s information resources and needs. DBA’s duties include:

Scheme definition Storage structure and access method definition Granting user authority to access the database Specifying integrity constraints Acting as liaison with users Monitoring performance and responding to changes in

requirements

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Database Users

Differentiated by the how they interact with the system

Naïve users: invoke pre-determined application with high-level user interface

Application programmers; Use DML calls, embedded calls

Sophisticated users: managers, decision support systems: request using query languages

Specialized users: design and write specialized applications.

Links/support

https://wiki.cse.buffalo.edu/services/content/how-use-jdbc-oracle

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Simple Database ApplicationAPPLICATION

DBMS DB

Ex: AccessOracleMySql

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Multi-Databases

APPLICATION

DBMS 1

DBMS 2

DBMS 3

DB

DB

DB

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Standard Access to DBAPPLICATION

DRIVER

MGR

DBMSDriver 1

DBMSDriver 2

DBMSDriver 3

DBMS 1

DBMS 2

DBMS 3

DB

DB

DB

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ODBC Architecture

Application

Class1 Class2

Driver Manager

DriverType1 DriverType2 DriverType3

DataSource2DataSource1DataSource3

ODBC

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Open Database Connectivity (ODBC) Standard

ODBC standard is an interface by which application programs can access and process SQL databases in a DBMS-independent manner. It contains:

A Data Source that is the database, its associated DBMS, operating system and network platform

A DBMS Driver that is supplied by the DBMS vendor or independent software companies

A Driver Manager that is supplied by the vendor of the O/S platform where the application is running

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ODBC Interface

It is a system independent interface to database environment that requires an ODBC driver to be provided for each database system from which you want to manipulate data.

The database driver bridges the differences between your underlying system calls and the ODBC interface functionality.

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An Example

Application DriverManager

DB2 driver MYSQL driver Oracle driver

odbc standard

API

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Application in Java

Application inJava DriverManager

Access driver MYSQL driver Oracle driver

odbc standard

API

jdbc API

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Java Support for ODBC : JDBC

When applications written in Java want to access data sources, they use classes and associated methods provided by Java DBC (JDBC) API.

JDBC is specified an an “interface”. An interface in Java can have many

“implementations”.So it provides a convenient way to realize

many “drivers”

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Java Support for SQL

Java supports embedded SQL.Also it provides an JDBC API as a standard

way to connect to common relational databases.

You need a JDBC:ODBC bridge for using the embedded SQL in Java.

Java.sql package and an extensive exception hierarchy.

We will examine incorporating this bridge using sample code.

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Data Source

Local relational database; Ex: OracleRemote relational database on a

server; Ex: SQLserverOn-line information service; Ex: Dow

Jones, Customer database

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Data Source and Driver

Data source is the data base created using any of the common database applications available.

Your system should have the driver for the database you will be using.

For example your Windows system should have the MS Access Driver.

There are a number of JDBC drivers available. On the IDE you are using you will install the

appropriate driver.

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JDBC Components Driver Manager: Loads database drivers, and

manages the connection between application & driver. Driver: Translates API calls to operations for a specific

data source. Connection: A session between an application and a

driver. Statement: A SQL statement to perform a query or an

update operation. Metadata: Information about the returned data, driver

and the database. Result Set : Logical set of columns and rows returned

by executing a statement.

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JDBC Classes

Java supports DB facilities by providing classes and interfaces for its components

DriverManager classConnection interface (abstract class)Statement interface (to be

instantiated with values from the actual SQL statement)

ResultSet interface

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Driver Manager Class

Provides static, “factory” methods for creating objects implementing the connection interface. Factory methods create objects on

demandwhen a connection is needed to a DB

driver, DriverManager does it using it factory methods.

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Connection interface

Connection class represents a session with a specific data source.

Connection object establishes connection to a data source, allocates statement objects, which define and execute SQL statements.

Connection can also get info (metadata) about the data source.

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Statement interface

Statement interface is implemented by the connection object.

Statement object provides the workspace for SQL query, executing it, and retrieving returned data.

SELECT {what} FROM {table name} WHERE {criteria} ORDER BY {field}

Queries are embedded as strings in a Statement object.

Types: Statement, PreparedStatement, CallableStatement

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ResultSet interface

Results are returned in the form of an object implementing the ResultSet interface.

You may extract individual columns, rows or cell from the ResultSet using the metadata.

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JDBC Application Architecture

Application

Connection

Driver Manager

Driver Driver Driver

DataSourceDataSourceDataSource

Statement Result Set

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JDBC Programming Steps

Import necessary packages; Ex: import java.sql.*; Load JDBC driver(driver should have been

installed) Data source and its location should have been

registered. Allocate Connection object, Statement object and

ResultSet object Execute query using Statement object Retrieve data from ResultSet object Close Connection object.

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Identifying Data Sources

It is specified using URL format.<scheme>: <sub_scheme>:<scheme-

specific-part>Example(for local source):

jdbc:odbc:tech_booksAlternatively, for remote connection,jdbc:odbc://bina.cse.buffalo.edu:4333/

tech_books

Summary

We learned the inner details of the relational database model

We also studied methods for programmatically accessing the data sources from Java language

This is just one persistence model. We will revisit data/storage later on in

the semester in the “big-data” context.

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