Languages and tools for web programming

Languages and Tools
for
Web Programming
Mrs. Alamelu.G
Assistant professor of BCA
E.M.G Yadava Women’s College
Madurai.

History of the Web
• Internet (1960s)
• World Wide Web - WWW (1991)
• First Web Browser - Netscape,
1994
• Google, 1998
• Facebook, 2004
• Smartphones (iPhone), 2007
• Tablets (iPad), 2010

Web programming
Web services vs. "classical" web programming
Client vs. server programming
client: JavaScript, Java
HTML-centric vs. program-centric
HTML-centric: PHP, ASP
cgi, fast-cgi
(Java) servlet
data model: Java servlet, database

Web services vs. web programming
web services = remote procedure call
we saw SOAP
structured data (XML)
methods and responses
generally, for machine consumption
web programming  generate HTML pages
for humans
often, database-driven
replacement for IBM 3270 terminals ...

Client vs. server programming
Execute code on client:
download Java applet  self-contained
programming environment
JavaScript (aka ECMAscript):
modify and get values from HTML
("document object model" – DOM)
Execute code on server  generate document
state maintenance (HTTP stateless)
login, shopping cart, preferences

Serving HTML Pages
HTML page includes image, audio, and video files.
All of this content lives on a web server—a remote
machine often far away from Client computer.
Client use a web browser to request, retrieve, and
eventually display web content on the screen.

What is HTML?
HTML is a language for describing web
pages.
HTML stands for Hyper Text Markup
Language.
HTML is not a programming language, it is
a markup language.
A markup language is a set of markup tags.
HTML uses markup tags to describe web
pages

Structure of an HTML page
<html>
<head> information about the page </head> <body> page
contents </body>
</html>
The header describes the page and the body contains the
page's contents an HTML page is saved into a file ending
with extension .html

Common Gateway Interface (CGI)
The interface specification that defines how information can be
passed from the browsers back to the server is called the Common
Gateway Interface, (CGI).

Processing dynamic pages
1. Web browser requests dynamic page.
2.Web server finds page and passes it to application server.
3. Application server scans page for instructions and finishes page.
4. Application server passes finished page back to web server
5. Web server sends finished page to requesting browser

Web Application
A web application is a website that contains pages with partly or final
content of a page.
The final content of a page is determined only when the visitor requests a
page from the web server.
A dynamic page which is the final content of the page that have varies of
from request based on the visitor’s actions.
Web applications are built to address a variety of challenges and problems

Common gateway interface (cgi)
Earliest attempt at dynamic web content
language-independent
passes HTTP request information via
command line (ISINDEX) – rarely used
environment variables: system info + query string (GET)
request body (POST)  standard input
return HTML or XML via standard output
non-parsed headers (NPH) return complete response

SQL architecture
 library interface
 proprietary
 JDBC, ODBC
 driver that connects (via TCP) to database
 same or different host
 issue queries, get results
 modify content
 transactions

SQL basics
• Integer: tinyint, smallint, mediumint, int(eger),
bigint
• Floating point: float, double, real
• Decimal: decimal(m,d) (for $)
• Date: date, datetime, timestamp, time, year
• String: char(N), varchar(N), tinyblob, tinytext,
blob, text, enum, set

SQL basics
 Retrieval: SELECT field1, field2 FROM table
WHERE condition ORDER BY expression
 Insertion: INSERT table SET
field1=value1,field2=value2, ...
 Update: UPDATE table SET field1=value1,
field2=value2 WHERE expression
 Delete row: DELETE FROM table WHERE
expression

Servlet life cycleRetrieval
 server application loads ServletClass
 creates instance via no-args constructor
 servers call servlet's init() method
 server calls service(req, res) method for each
request (often, with class name as URL), possibly
concurrently
 servers calls destroy() on shutdown

HTTP requests as servlets
 HTTP method GET, PUT, POST, ...  doGet,
doPut, doPost
 subclass of HttpServlet overrides default
implementation

n-tier architecture
client tier:
receives user events (keyboard, mouse)
presentation of data
user interface
e.g., Java applets, web browser, thin client
application
application-server tier:
"business logic"  actual data processing,
algorithms
can be component-based (Java Beans)

n-tier architecture
 Data-server tier
 data storage
 relational and legacy databases
 all tiers could run on same machine, but usually
separated
 HTTP (or SOAP) from client to server
 Corba or SOAP or remote-SQL between server
tiers
 Advantages:
 independent of storage model
 simpler authentication to database

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