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 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.
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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
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Object relational model
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Entity-Relationship Model
SSN
street
number
balance
city
name
customer
depositor
account
entity
attribute
relationship
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Relational Model
Customer Table
Name
Johnson
SSN
192-83-7465
street
Alma
city
Palo Alto
account no.
A-101
Account Table
Account No.
A-101
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Balance
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
Language
Language 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
data
Query language (sequential query
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language: sql) : insert data, update data
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Relational Algebra
Tables representing relations
Row uniquely identified by a primary key
Related tables are associated using
foreign keys
Special 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 Model
Naïve users
Query processing
Application
interfaces
Object code
Application
programmers
Sophisticated
users
Application
programs
query
Embedded
DML compiler
DML
compiler
DBA
Database scheme
DDL
interpreter
Query evaluation
engine
Transaction
manager
DBMS
System
Buffer manager
File manager
Data files
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indices
Statistical data
Data dictionary
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.
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Links/support
 https://wiki.cse.buffalo.edu/services/content/how-use-jdbc-oracle
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Simple Database
Application
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DBMS
DB
Ex: Access
Oracle
MySql
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Multi-Databases
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DBMS 1
DBMS 2
DBMS 3
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DB
DB
DB
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Standard Access to DB
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D
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V
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G
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DBMS
Driver 1
DBMS 1
DB
DBMS
Driver 2
DBMS 2
DB
DBMS 3
DB
DBMS
Driver 3
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ODBC Architecture
Application
Class1
Class2
ODBC
Driver Manager
DriverType1
DataSource1
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DriverType2
DataSource2
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DriverType3
DataSource3
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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
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MYSQL driver
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Oracle driver
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Application in Java
Application in
Java
DriverManager
Access driver
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MYSQL driver
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Oracle driver
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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: Oracle
Remote relational database on a server;
Ex: SQLserver
On-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 class
Connection 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 demand
when 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 B.Ramamurthy
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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
Result Set
Statement
Driver Manager
Driver
DataSource
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Driver
DataSource
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Driver
DataSource
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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-specificpart>
Example(for local source): jdbc:odbc:tech_books
Alternatively, for remote connection,
jdbc:odbc://bina.cse.buffalo.edu:4333/tech_books
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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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