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
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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
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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
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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
S Q L ke yw o rd
SELEC T FR O M
W HERE
ORDER BY
IN S E R T IN T O
UPDATE
D e scrip tio n
S e le ct (re trie v e ) fie ld s fro m o n e o r m o re ta b le s.
C rite ria fo r se le ctio n th a t d e te rm in e th e ro w s to b e
re trie ve d .
C rite ria fo r o rd e rin g (so rtin g ) o f re co rd s.
In se rt va lu e s in to o n e o r m o re ta b le s. [N o te : S o m e
d a ta b a se s d o n o t re q u ire th e S Q L ke yw o rd IN T O .]
U p d a te e xistin g d a ta in o n e o r m o re ta b le s.
(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;
}
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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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