Networked
Applications
Chapter 11
Copyright 2001 Prentice Hall
The Primacy of Applications
•
Users only care about
applications
•
The other layers (transport, internet, data
link, physical) exist only to support
applications
Applications in this Chapter
•
There are many applications
•
We will only look at 3 networked
applications
–
Web
-
enabled database access
–
Internet E
-
mail
–
IP telephony for voice
-
data convergence
•
Each is important
•
Each has general lessons to teach
Web
-
Enabled Database Access
Web
-
Enabled Database Access
•
Problem: Database is on a “
database
server
”
–
Mainframe or client/server server
–
These need proprietary client software or a
terminal
•
Problem: Most users only have browsers
User with Browser
Database Server
Web
-
Enabled Database Access
•
Solution: an
application server
(webserver
with intermediary software) mediates
between the two
User with Browser
Database Server
Application Server
Web
-
Enabled Database Access
•
Step 1: User types URL of data entry form
•
Step 2: Webserver application sends form
User with Browser
Database Server
URL
Form
Application Server
Web
-
Enabled Database Access
•
Step 3: User types information in form, hits Send
–
Browser puts data in a request line
–
GET keyword
–
/cgi
-
bin is the absolute path to a directory holding an
intermediary program,
bogo.exe
GET /cgi
-
bin/bogo.exe?last=Lee&first=Pat
Web
-
Enabled Database Access
•
Step 3: User types information in form, hits
Send
–
Data separated from absolute path by ?
–
last
field contains the value
Lee
–
first
field contains the value
Pat
GET /cgi
-
bin/bogo.exe?last=Lee&first=Pat
Web
-
Enabled Database Access
•
Step 3: Application server webserver
software passes data form to the
intermediary program
, Bogo.exe, on the
webserver
Application Server
Webserver
Application
Software
Intermediary
Program
(Bogo.exe)
Web
-
Enabled Database Access
•
Step 4: Bogo.exe puts the data into a
query in the database server’s
standard
format
–
Sends the query to the server
User with Browser
Database Server
Standard
Query
Application Server
(Bogo.exe)
Web
-
Enabled Database Access
•
Step 5: Database server sends response in
its
standard format
to the intermediary
program, Bogo.exe
User with Browser
Database Server
Standard
Response
Application Server
(Bogo.exe)
Web
-
Enabled Database Access
•
Step 6: Application server intermediary
software (Bogo.exe)
creates a new HTML
webpage
containing the response
Application Server
Intermediary
Program
(Bogo.exe)
Webpage
Web
-
Enabled Database Access
•
Step 7: Application server intermediary
software passes this webpage to the
webserver application program
Application Server
Webserver
Application
Software
Intermediary
Program
(Bogo.exe)
Webpage
Web
-
Enabled Database Access
•
Step 8: Webserver application program
passes the webpage to the browser
User with Browser
Database Server
Webpage
Application Server
Transparency
•
Browser does not know that it is dealing with a
database server; it sends standard webserver
commands, gets webpages back
•
Database server does not know it is dealing with
a browser; receives standard database server
requests, sends standard database server
responses
•
No changes are needed in the browser or
database application software; process is
transparent
to both the browser and the
database server
Web
-
Enabled Database Access
•
CGI and Intermediary Program
–
Intermediary program
(Bogo.exe) does the
actual translation work
Webserver
Application
Program
Intermediary
Program
(Bogo.exe)
Database
Application
Program
Web
-
Enabled Database Access
•
CGI and Other Programs
–
Webserver application programs have a
standardized way of moving data to and from
other programs
•
Common Gateway Interface (CGI)
standard
Webserver
Application
Program
Intermediary
Program
(Bogo.exe)
Database
Application
Program
CGI
Web
-
Enabled Database Access
•
CGI
–
Starts a new copy of the intermediary program
every time the intermediary program is called
–
This is very slow
–
OK only for small applications
Webserver
Application
Program
Intermediary
Program
(Bogo.exe)
Database
Application
Program
CGI
Intermediary
Program
(Bogo.exe)
Intermediary
Program
(Bogo.exe)
Web
-
Enabled Database Access
•
Application Program Interfaces (APIs)
–
Database servers have
proprietary
ways of
communication with other application programs
–
Other application program sends an
application
program interface (API)
call to the database
program
Webserver
Application
Program
Database
Application
Program
API
Web
-
Enabled Database Access
•
Application Program Interfaces (APIs)
–
Faster
than CGI but
proprietary
–
Webserver applications do not support all
database APIs
Webserver
Application
Program
Database
Application
Program
API
Web
-
Enabled Database Access
CGI
API
Speed
Slower
Faster
Generality
General
Proprietary
Web
-
Enabled Database Access
•
Client
-
Side Processing
–
Webserver can download webpage with Java
or Active
-
X program
–
Client can then
communicate directly
with
the database server
User with Browser
Database Server
Webpage with
Java applet
Subsequent Interactions
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