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Lecture 8 Accessing Database
 Database server
 Application access to the database:

Open Database Connectivity
 Accessing Database using Perl Script
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1. Web Architecture
 Three-tier architecture:
 Presentation: clients contains both the presentation and
application logic components.
 Content: web server provides interactive view of information
form a data store.
 Data and service level: provides data for the web server.
HTTP request
HTTP response
Database
server
Internet
Client computers
with web browsers
Web server
Presentation level
Content level
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Data and service
level
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1.1. Database
 Database
 Integrated collection of data
 Database Management System (DBMS)
 Has mechanisms for storing and organizing data
 Allows sophisticated queries and manipulations of data
 Database applications:
 Banking: all transactions
 Airlines: reservations, schedules
 Universities: registration, grades
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1.1. Database
 Architecture for a database system
view level
view 1
view 1
view n
logical
level
physical
level
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1.1. Database
 Architecture for a database system
 Physical
level describes how a record is stored.
• single file: MS Access, Lotus Approach, MS Fox Pro, Paradox
• true data server (multiple files): MySQL, Oracle, Sybase
Logical level describes data stored in database,
and the relationships among the data.
 View level: application programs hide details of
data types.

• Views can hide information (e.g. salary) for security
purposes.
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1.1.1. Relational Database Model
 Relational Database Model
 Most popular database system in use today
 Logical representation of the data
 Consider relationships between data without worrying about
physical implementation
 Relational Database
 Composed of tables
 Any row of the table is called a record
 The first field is used as the primary key for referencing
• Records are normally unique (by primary key)
• Primary key can be composed of more than one field or column

Each column represents a different field (or attribute)
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1.1.1. Relational Database Model
 Example of Relational Database Structure
Attributes
A record
customer-id
10001
10002
10003
10004
10005
customer-name
Zhang, Stephen
Ho, Ricky
Chau, Anthony
Wong, Michael
Tsang, Daniel
Primary Key
INE1020: Introduction to Internet Engineering
district
Kowloon
NT
HK
Kowloon
NT
phone-no
9843-9893
9873-1341
2344-0979
2878-4323
2134-4532
account-no
A-201
A-217
A-222
A-103
A-234
A column
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1.1.1. Relational Database Model
 Example of Relational Database Structure


Physical level: Microsoft Access - banking.mdb
Logical level:
• Three tables: Customer, Account and Balance
• The primary key in Customer table is customer-id.
Table: Account
Table: Customer
customer-id
10001
10002
10003
10004
10005
customer-name
Zhang, Stephen
Ho, Ricky
Chau, Anthony
Wong, Michael
Tsang, Daniel
district
Kowloon
NT
HK
Kowloon
NT
phone-no
9843-9893
9873-1341
2344-0979
2878-4323
2134-4532
INE1020: Introduction to Internet Engineering
customer-id account-no
10001
A-201
10002
A-217
10002
A-300
10003
A-222
10003
A-239
10004
A-103
10005
A-109
10005
A-234
Table: Balance
account-no
A-103
A-109
A-201
A-217
A-222
A-234
A-239
A-300
balance
850
400
700
300
100
1200
450
500
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1.1.1. Relational Database Model

Relationships among the three tables:
• Lines between tables represent relationships
– Example: Line between Customer and Account
» One-to-many relationship
» Every customer can have a number of accounts.
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1.1.1. Relational Database Model

View level: join Customer and Account tables.
Attributes
A record
customer-id
10001
10002
10003
10004
10005
customer-name
Zhang, Stephen
Ho, Ricky
Chau, Anthony
Wong, Michael
Tsang, Daniel
Primary Key
INE1020: Introduction to Internet Engineering
district
Kowloon
NT
HK
Kowloon
NT
phone-no
9843-9893
9873-1341
2344-0979
2878-4323
2134-4532
account-no
A-201
A-217
A-222
A-103
A-234
A column
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1.1.1. Relational Database Model
 Different users interested in different parts of the
table

Needs a data manipulation or query language - to access and
manipulate the data from the table/database
 Structured Query Language (SQL – pronounced “sequel”)
 The most widely used query language.
 Provides complete set of keywords
 Allows smaller databases to be combined to form larger ones
 Results of a query called result sets (or record sets)
• e.g. Result set to show the customers who stay in Kowloon
customer-id district
10001
Kowloon
10004
Kowloon
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1.1.2. Structured Query Language
 Structured Query Language (SQL) keywords used to
 Query a database
 Insert records into a database
 Update existing records in a database
SQL keyword
SELECT FROM
WHERE
ORDER BY
INSERT INTO
UPDATE
Description
Select (retrieve) fields from one or more tables.
Criteria for selection that determine the rows to be
retrieved.
Criteria for ordering (sorting) of records.
Insert values into one or more tables. [Note: Some
databases do not require the SQL keyword INTO.]
Update existing data in one or more tables.
(Note: there are other keywords not included in this table)
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1.1.2 SELECT Query
 SELECT * FROM TableName


TableName specifies table in database where data is located
* selects all rows and fields from TableName
 SELECT * FROM Customer

Selects the entire contents of the customer table
 SELECT customer-id, customer-name FROM
Customer


To select fields from table, replace * with comma-separated list of
field names to select
Returns the following:
customer-id customer-name
10001
10002
10003
10004
10005
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Zhang, Stephen
Ho, Ricky
Chau, Anthony
Wong, Michael
Tsang, Daniel
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1.1.2 SELECT Query
 WHERE clause



Most cases, only necessary to locate records that satisfy certain
selection criteria
SQL uses the WHERE clause to specify the selection criteria
Can contain operators
• <, >, <=, >=, =, <> and LIKE
 Simplest form:
 SELECT fieldName1, fieldName2, … FROM TableName WHERE
Criteria
 e.q. SELECT customer-id, district FROM customer WHERE
district = “KOWLOON” return the followings:
customer-id district
10001
Kowloon
10004
Kowloon
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1.1.2 SELECT Query
 ORDER BY clause
 Sorts results of query into ascending or descending order
SELECT fieldName1, fieldName2, … FROM TableName ORDER BY fieldName
ASC
SELECT fieldName1, fieldName2, … FROM TableName ORDER BY fieldName
DESC
 Example
SELECT customer-id, customer-name FROM Customer
ORDER BY customer-name ASC
 Returns customers sorted by customer name in ascending
order
customer-id
10003
10002
10005
10004
10001
customer-name
Chau, Anthony
Ho, Ricky
Tsang, Daniel
Wong, Michael
Zhang, Stephen
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1.1.2 Inserting a Record
 INSERT INTO operation
 Inserts data into the table (e.g; adds a record)
 Simplest form:
Table into
which record
will be inserted
List of field names into
which to insert values
(not required if inserting
complete record)
INSERT INTO TableName ( fieldName1, fieldName2, …, fieldNameN )
Values ( value1, value 2, …, valueN )
KEYWORDS

Values to be inserted into fields
– in order of fields listed before
The single quote character should be used as a delimiter for
strings to be inserted into the database
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1.1.2 Inserting a Record
 Sample insert operation
INSERT INTO Customer ( customer-id, customername, district, phone-no )
Values (10006, ‘Kwok, Charles’, ‘NT’, ‘9342-9432’)
 Results:
Newly added
record
customer-id
10001
10002
10003
10004
10005
10006
customer-name
Zhang, Stephen
Ho, Ricky
Chau, Anthony
Wong, Michael
Tsang, Daniel
Kwok, Charles
INE1020: Introduction to Internet Engineering
district
Kowloon
NT
HK
Kowloon
NT
NT
phone-no
9843-9893
9873-1341
2344-0979
2878-4323
2134-4532
9342-9432
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1.1.2 Updating a Record
 Modify a record with the UPDATE operation
UPDATE TableName
SET fieldName1 = value1, fieldName2 = value2, …,
fieldNameN = valueN
WHERE criteria
 Example:
UPDATE Customer
SET phone-no = ‘9434-4321’
WHERE customer-id = 10003
 Change phone number value for the customer id = 10003
from 2344-0979 to 9434-4321.
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1.1.2 Updating a Record
 Old table:
customer-id
10001
10002
10003
10004
10005
10006
customer-name
Zhang, Stephen
Ho, Ricky
Chau, Anthony
Wong, Michael
Tsang, Daniel
Kwok, Charles
district
Kowloon
NT
HK
Kowloon
NT
NT
phone-no
9843-9893
9873-1341
2344-0979
2878-4323
2134-4532
9342-9432
district
Kowloon
NT
HK
Kowloon
NT
NT
phone-no
9843-9893
9873-1341
9434-4321
2878-4323
2134-4532
9342-9432
 New table:
customer-id
10001
10002
10003
10004
10005
10006
customer-name
Zhang, Stephen
Ho, Ricky
Chau, Anthony
Wong, Michael
Tsang, Daniel
Kwok, Charles
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2 Application Access to the Database
 Microsoft Universal Data Access (UDA)
 Architecture
designed for high-performance data
access to different data sources.
Application or Browser
ADO
OLE DB
ODB
C
Relational data sources
Mainframe/legacy data
Non-relational data sources
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2. Application Access to the Database
 UDA consists of three primary components
 OLE DB (Object Linking and Embedding DB)
• Core of UDA architecture
• Provides low-level access to any data source

ODBC (Open Database Connectivity)
• API (Application Programming Interface) or programming
language library written in C
• Developed by Microsoft to allow Windows applications to
communicate in a uniform manner with relational databases
• Uses SQL to access data

ADO (ActiveX Data Objects)
• Simple object model
• Provides uniform access to any data source by interacting with
OLE DB
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2. Application Access to the Database
 Two common methods:
 ODBC
approach - e.g. using Perl scripts (red line).
 ADO approach - e.g. using ASP (blue line).
Application or Browser
ADO
OLE DB
ODB
C
Relational data sources
Mainframe/legacy data
Non-relational data sources
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2.1. ODBC Approach
 ODBC (Open Database Connectivity)
 API (Application Programming Interface) or programming
language library written in C
 Uses SQL to access data
 ODBC Driver written by vendors
 Uses ODBC API to provide uniform access to the database
 To execute an SQL query
 Program must be able to access the database
• Database must be given a System Data Source Name (DSN) on
the server
• Database must be registered as an ODBC source
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2.1. Registering a Database
 Specific instructions for Windows 98/2000:
 double-click the ODBC Data Sources (32 bit) icon in the
Windows Control Panel to display the ODBC Data Source
Administrator dialog.
Click the System DSN
tab to view a list of all
systems DSNs.
 Select the name to the
right of Microsoft Access
Driver (*.mdb) from the
list.

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2.1. Registering a Database

Click Add… to display the Create New Data Source dialog.
Select Microsoft Access Driver (*.mdb) and click Finish to
display the ODBC Microsoft Access Setup dialog.
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2.1. Registering a Database

Enter the Data Source Name and Description field. Click
the Select… button to display the Select Database dialog.
Select the database that you want. Click OK to close this
dialog.
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2.1. Registering a Database

The Banking DSN is now listed.
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3. Accessing Database using Perl Script
 After registering database as ODBC source, we can
access it using Perl scripts.
 Perl package Win32-ODBC

Enables Perl programs to connect to ODBC data sources
 Example: From Web browser
1. Client enters SQL query string
2. String sent to Web server
3. Perl script executed
• Database queried
4. Record set in HTML form sent back to client
• Use tables to output fields in a database
– Organizes information neatly
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3. Accessing Database using Perl Script
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3. Accessing Database using Perl Script
 Example of how to access database by using HTML
form and Perl scripts.
<HTML>
<HEAD>
<TITLE>Sample Database Query</TITLE>
</HEAD>
<BODY BACKGROUND = "images/back.gif">
<BASEFONT FACE = "ARIAL,SANS-SERIF" SIZE = 2>
<FONT SIZE = +2>
<STRONG>Querying an ODBC database.</STRONG>
</FONT><BR>
<FORM METHOD = "POST" ACTION = "cgi-bin/data.pl">
<INPUT TYPE = "TEXT" NAME = "QUERY" SIZE = 40
VALUE = "SELECT * FROM CUSTOMER"><BR><BR>
<INPUT TYPE = "SUBMIT" VALUE = "Send Query">
</FORM>
</BODY>
</HTML>
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Insert and
define text
INPUT for
entering SQL
query
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3. Accessing Database using Perl Script
 Script output:
CUSTOMER
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3. Accessing Database using Perl Script
 Perl scripts:
# Program to query a database and send results to the client.
use Win32::ODBC;
use CGI qw (:standard);
$querystring = param(QUERY);
$DSN = "Banking";
print header;
if (!($Data = new Win32::ODBC($DSN))) {
print "Error connecting to $DSN\n";
print "Error: " . Win32::ODBC::Error() . "\n";
exit;
}
if ($Data->Sql($querystring)) {
print "SQL failed.\n";
print "Error: " . $Data->Error() . "\n";
$Data->Close();
exit;
}
INE1020: Introduction to Internet Engineering
Specifies that a new
instant of the object
is to be created
Query string sent to
the database
If fails, error message
is returned
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3. Accessing Database using Perl Script
print "<BODY BACKGROUND = \"/images/back.gif\">";
print "<BASEFONT FACE = \"ARIAL,SANS-SERIF\" SIZE = 3>";
print "<FONT COLOR = BLUE SIZE = 4> Search Results </FONT>";
$counter = 0;
print "<TABLE BORDER = 0 CELLPADDING = 5 CELLSPACING = 0>";
while($Data->FetchRow()) {
%Data = $Data->DataHash();
@key_entries = keys(%Data);
print "<TR>";
foreach $key( keys( %Data ) ) {
print "<TD BGCOLOR = #9999CC>$Data{$key}</TD>";
}
print "</TR>";
$counter++;
Retrieves the fields in
a row from the record
set
Coding HTML in Perl
open using print header
close using print
end_html
}
print "</TABLE>";
print end_html;
$Data->Close();
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3. Accessing Database using Perl Script
 Error() - Returns the last encountered error
 FetchRow() - Retrieves the next record from the




keyset.
DataHash() - Returns the contents for the entire
row from the record set
keys() - Returns an unordered array containing all
keys in a hash
Close() - Closes the ODBC connection
new - Creates a new ODBC connection based on DSN
(Data Source Name)
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3. Accessing Database using Perl Script
 Script output:
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Further Readings
 Note: This topic is designed with the
objective of providing an introduction to
accessing database using perl scripts.
 Students who wish to invest more time on
studying advanced features and topics of
ODBC and accessing databases are referred
to the following resources:
Deitel Chapter 22
 http://aspn.activestate.com/ASPN/Reference/Pro
ducts/ActivePerl/site/lib/Win32/ODBC.html
 http://aspn.activestate.com/
 http://www.roth.net/perl/odbc/faq/

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