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Net Centric Computing


1. HTTP Protocol

HTTP is the foundation of data communication for the in the World Wide Web
HTTP functions as a request-response protocol in the client-server computing Model. In HTTP, a web browser for example, acts as a client, while an application running on a computer hosting a website functions as a server. The client submits an HTTP request message to the server. The server, which stores content, or provides resources, such as HTML files or performs other functions on behalf of the client, returns a response message to the client. A response contains completion status information about the request and may contain any content requested by the client in its message body.
It is a stateless protocol, you send request and it responds does not maintain any state. To maintain the state, we can use
a) Session Object in the server side
b) Cookies in the client side.
c) Hidden variables in the form

2. Static and Dynamic Pages

Static Web Pages
A static web page (sometimes called a flat page) is a web page that is delivered to the user exactly as stored, in contrast to dynamic web pages which are generated by a web application. Consequently a static web page displays the same information for all users, from all contexts, subject to modern capabilities of a web server to negotiate content-type or language of the document where such versions are available and the server is configured to do so. Static web pages are often HTML documents stored as files in the file system and made available by the web server over HTTP.

• No programming skills are required to create a static page.
• Inherently publicly cacheable (ie. a cached copy can be shown to anyone).
• No particular hosting requirements are necessary.
• Can be viewed directly by a web browser without needing a web server or application server

• Any personalization or interactivity has to run client-side (ie. in the browser), which is restricting.
• Maintaining large numbers of static pages as files can be impractical without automated tools.

Dynamic Web pages
A dynamic web page is a kind of web page that has been prepared with recent information, for each individual viewing. It changes with the time. For ex. News content, events. The content of the site changes when the user logs in and logs out. Page contents are displayed according to the location of the user. In facebook, you can see suggestions to add friends since it knows your friends and those are mostly friend of your friends. Facebook gets updated with recent feeds etc.
Dynamic web pages can be created in two ways
1. Client-Side Scripting
Using client-side scripting to change interface behaviors within a specific web page, in response to mouse or keyboard actions or at specified timing events. In this case the dynamic behavior occurs within the presentation.
Client-Side scripting languages like JavaScript or Actionscript, used for DHTML and Flash technologies respectively, are frequently used to play with the media types (sound, animations, changing text, etc.) of the presentation
The Client-side content is generated on the user's computer. The web browser retrieves a page from the server, then processes the code embedded in the page (often written in JavaScript) and displays the retrieved page's content to the user.

2.Server-Side Scripting
A program running on the web server (server-side scripting) is used to change the web content on various web pages, or to adjust the sequence of or reload of the web pages. Server responses may be determined by such conditions as data in a posted HTML form, parameters in the URL, the type of browser being used, the passage of time, or a database or server state. Such web pages are often created with the help of server-side languages such as ASP, PHP, JSP etc.

3.Combined Client Side and Server Side
Ajax is a web development technique for dynamically interchanging content with the server-side, without reloading the web page. Google Maps is an example of a web application that uses Ajax techniques and database.

Search engines work by creating indexes of published HTML web pages that were, initially, "static". With the advent of dynamic web pages, often created from a private database, the content is less visible. Unless this content is duplicated in some way (for example, as a series of extra static pages on the same site), a search may not find the information it is looking for. It is unreasonable to expect generalized web search engines to be able to access complex database structures, some of which in any case may be secure.

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