Study of Web Servers / Web Browser and Tools for Enterprise Software Development and Deployment

Aim: To Study about Web Browser and Web Server Concepts and tools for Enterprise Software development and deployment.

Web browser:

A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier (URI) and may be a web page, image, video, or other piece of content. Hyperlinks present in resources enable users to easily navigate their browsers to related resources.

Although browsers are primarily intended to access the World Wide Web, they can also be used to access information provided by Web servers in private networks or files in file systems. Some browsers can be also used to save information resources to file systems.

Function:

The primary purpose of a web browser is to bring information resources to the user. This process begins when the user inputs a Uniform Resource Identifier (URI), for example http://en.wikipedia.org/, into the browser. The prefix of the URI determines how the URI will be interpreted.

The most commonly used kind of URI starts with http: and identifies a resource to be retrieved over the Hypertext Transfer Protocol (HTTP). Many browsers also support a variety of other prefixes, such as https: for HTTPS, ftp: for the File Transfer Protocol, and file: for local files.

Features:

All major web browsers allow the user to open multiple information resources at the same time, either in different browser windows or in different tabs of the same window.Available web browsers range in features from minimal, text-based user interfaces with bare-bones support for HTML to rich user interfaces supporting a wide variety of file formats and protocols.

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Browsers which include additional components to support e-mail, Usenet news, and Internet Relay Chat (IRC), are sometimes referred to as "Internet suites"

Most web browsers can display a list of web pages that the user has bookmarked so that the user can quickly return to them. Bookmarks are also called "Favorites" in Internet Explorer. In addition, all major web browsers have some form of built-in web feed aggregator.

Web server:

A web server is computer program that delivers (serves) content, such as web pages, using the Hypertext Transfer Protocol (HTTP), over the World Wide Web. The term web server can also refer to the computer or virtual machine running the program. In large commercial deployments, a server computer running a web server can be rack-mounted with other servers to operate a web farm.

Principles:

Internet the web, rely on client-server architecture. This architecture means that a server offers web services such as web page, video, music to one or several clients. The advantage of client-server architecture is that several users located in several places with heterogeneous software and hardware could communicate and use common resources to collaborate and cooperate.

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Client-server architecture relies on the separation between server applications and client applications. The server hosts heavy infrastructure of application, those which generates all services. Client hosts only browsing materials of the graphical interface generated by the server, usually a web browser, a mail client.

Web server architecture relies basically on the following principle:

 An operating system that manages hardware resources (the computer) and offers services to high level applications.

 A web server application and a database server application that use operating system services and offers services to high level applications.

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Overview:

The primary function of a web server is to deliver web pages to clients. This means delivery of HTML documents and any additional content that may be included by a document, such as images, style sheets and JavaScript.

A client, commonly a web browser or web crawler, initiates communication by making a request for a specific resource using HTTP and the server responds with the content of that resource, or an error message if unable to do so.

While the primary function is to serve content, a full implementation of HTTP also includes a way of receiving content from clients. This feature is used for submitting web forms, including uploading of files.

Many generic web servers also support server-side scripting, e.g., Apache HTTP Server and PHP. This means that the behavior of the web server can be scripted in separate files, while the actual server software remains unchanged.

Usually, this functionality is used to create HTML documents on-the-fly as opposed to return fixed documents. This is referred to as dynamic and static content respectively. The former is primarily used for retrieving and/or modifying information in databases. The latter is, however, typically much faster and easily cached.

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Uses:

 Web servers are not always used for serving the world wide web, but they can also be found embedded in devices such as printers, routers, webcams and serving only a local network.  The web server may then be used as a part of a system for monitoring and/or administrating the device in question.  This usually means that no additional software has to be installed on the client computer, since a only a web browser is required (which by now is included with most operating systems).

Common features:

1. Virtual hosting to serve many Web sites using one IP address. 2. Large file support to be able to serve files whose size is greater than 2 GB on 32 bit OS. 3. Bandwidth throttling to limit the speed of responses in order to not saturate the network and to be able to serve more clients. 4. Server-side scripting to generate dynamic Web pages, but still keeping Web server and Web site implementations separate from each other.

Path translation:

Web servers are able to map the path component of a Uniform Resource Locator (URL) into:

 A local file system resource (for static requests);  An internal or external program name (for dynamic requests).

For a static request the URL path specified by the client is relative to the Web server's root directory.

Consider the following URL as it would be requested by a client:

http://www.example.com/path/file.html

The client's user agent will translate it into a connection to www.example.com with the following HTTP 1.1 request:

GET /path/file.html HTTP/1.1

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Host: www.example.com

The Web server on www.example.com will append the given path to the path of its root directory. On Unix machines, this is commonly /var/www. The result is the local file system resource:

/var/www/path/file.html

The Web server will then read the file, if it exists, and send a response to the client's Web browser. The response will describe the content of the file and contain the file itself.

The Client Server Architecture:

The Internet revolves around the client-server architecture. Your computer runs software called the client and it interacts with software known as the server located at a remote computer. The client is usually a browser such as Internet Explorer, Netscape Navigator or Mozilla.

Browsers interact with the server using a set of instructions called protocols. These protocols help in the accurate transfer of data through requests from a browser and responses from the server. There are many protocols available on the Internet. The World Wide Web, which is a part of the Internet, brings all these protocols under one roof. You can, thus, use HTTP, FTP, Telnet, email etc. from one platform - your web browser.

Some common Internet protocols:

 HTTP (Hypertext transfer Protocol): used on the World Wide Web (WWW) for transferring web pages and files contained in web pages such as images.  FTP (File Transfer protocol): employed for transferring files from one machine to the other.  SMTP (Simple Mail Transport Protocol): used for email.  Telnet Protocol: Used to open telnet sessions.

Model #1 - Static HTML pages

The client (browser) requests for an HTML file stored on the remote machine through the server software. The server locates this file and passes it to the client. The client then displays this file on your machine. In this case, the

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HTML page is static. Static pages do not change until the developer modifies them.

Model #2 - CGI Scripts

The scenario is slightly different for CGI applications. Here the server has to do more work since CGI programs consume the server machine's processing power.

Let us suppose you come across a searchable form on a web page that runs a CGI program. Let us also suppose you type in the word 'computers' as the search query. Your browser sends your request to the server. The server checks the headers and locates the necessary CGI program and passes it the data from the request including your search query "computers". The CGI program processes this data and returns the results to the server. The server then sends this formatted in HTML to your browser which in turn displays the HTML page.

Thus the CGI program generates a dynamic HTML page. The contents of the dynamic page depend on the query passed to the CGI program.

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Model #3 - Server side scripting technologies

The third case also involves dynamic response generated by the use of server side technologies. There are many server side technologies today.

Active Server Pages (ASP): A Microsoft technology. ASP pages typically have the extension .asp.

Personal Home Pages (PHP): An open source technology. PHP pages typically have .php, .phtml or .php3 file name extensions.

Java Server Pages: jsp pages contain Java code.

Server Side Includes (SSI): Involves the embedding of small code snippets inside the HTML page. An SSI page typically has .shtml as its file extension.

Let's look at PHP as an example. A request sent for a PHP page from a client is passed to the PHP interpreter by the server along with various program variables. The interpreter then processes the PHP code and generates a dynamic HTML output. This is sent to the server which in turn redirects it to the client. The browser is not aware of the functioning of the server. It just receives the HTML code, which it appropriately formats and displays on your computer.

CONCLUSION:

Thus the web servers/web browser and tools for enterprise software development and deployment has been studied.