Understanding Internet and WWW

Internet and WWW

• The internet functions as a global network where interconnected computers use TCP/IP protocols for information exchange.
• No single entity has control, as different aspects are handled by different entities.
• IP addresses, like 148.78.250.12, identify each computer on a global scale.
• Common applications include WWW, file transfer, and electronic mail.

World Wide Web (WWW)

• The WWW is a system of interconnected hypertext documents (web pages) accessed through the internet.
• It operates on a client-server model where browsers act as clients to request and display web pages from web servers.
• A website is a collection of related web pages, usually identified by a domain name, published on the WWW.
• A homepage is the first page visitors encounter on a site, while a web page is a single document with text, multimedia, and hyperlinks.

Uniform Resource Locator (URL)

• A URL specifies the location of a resource on the WWW.
• URLs follow a standard format: Protocol://Domain name[:Port Number]/[Path][;Parameters][?Query String][#Fragment].
• Protocol defines the internet service type (e.g., http, https, ftp).
• The domain name or IP address identifies the web server hosting the resource (e.g., www.hanbit.co.kr or 61.72.250.71).
• DNS translates domain names into IP addresses.
• Port number (optional) specifies the server's communication port, such as :80 for HTTP or :443 for HTTPS.
• Path (optional) specifies the directory and file location of a resource on the server, defaulting to the root directory if omitted, with index.html often served as default.
• Common protocols:
  • www for web service using http, https, ftp.
  • Email for email service using SMTP, POP3.
  • FTP for file transfer service using ftp.

URL Example

• An example is https://cs.kw.ac.kr/main/main.php or https://www.google.com/search?q=Berners-Lee.
• The https part specifies the protocol for internet service communication.
• The domain name (cs.kw.ac.kr, www.google.com) identifies the web server.
• The rest of the URL is the path, which includes the directory and file location, along with any optional queries (e.g., ?q=Berners-Lee).

HTML (Hyper Text Markup Language)

• HTML is the standard markup language for creating web pages.
• HTML tags (markup symbols within angle brackets) instruct web browsers on how to display text, images, audio, and video.
• HTML tags usually come in pairs, such as (start tag) and (end tag).
• An example of HTML tag would be "This is a Heading" displayed as a heading or "This is a paragraph." displayed as a paragraph.
• Basic HTML tags:
  • `` specifies the document as a web page.
  • `` specifies descriptive information about the web documents.
  • `` specifies the visible part of a web document.

HTTP (Hyper Text Transfer Protocol)

• HTTP enables web servers and browsers to exchange documents, like HTML, over the web.
• HTTP operates as a request/response protocol in a client-server architecture where browsers act as clients and web servers as servers.
• When a user checks their bank balance:
  • The client sends the user's ID and password via an HTTP request to the bank server.
  • The server searches its database and sends the result as an HTTP response to the client.

HTTP Request and Response

• HTTP requests and responses use a generic message format with four components:
  • Start-line: Includes the request-line (e.g., GET /example-page HTTP/1.1) or status-line (e.g., HTTP/1.1 200 OK).
  • Header fields: Provide additional information about the request or response, such as content type and encoding methods.
  • Empty line: Indicates the end of the header fields.
  • Message-body: Optional data like user input or files and images.
• Common HTTP methods:
  • GET: Requests the specified resource from a server.
  • POST: Sends data to a server to create or update a resource.
  • HEAD: Similar to GET, but without the response body.
  • DELETE: Deletes the specified resource.
  • PATCH: Applies partial modifications to a resource.

HTTP Message

• HTTP request message example:
  • The URL /cgi-bin/process.cgi is used to process data sent to the server and returns a response accordingly.
  • Headers pass information to the server, and the content type specifies the format of data in the request body.
  • Body stores data sent using POST.
• HTTP response message example:
  • The status line (http/1.1 200 ok) provides the request outcome.
  • Headers provide information about the server and resource access.
  • Body can include HTML for the client.

Web Page Types

• Two types of web pages:
  • Static: A page transmitted as-is from the server, displaying fixed content for all users, created with HTML/CSS with no user interaction.
  • Dynamic: A page generated by a web application, displaying content based on user input, created with web programming techniques.

Web Programming Techniques

• Web programming enables flexible interaction beyond the capabilities of HTML.
• Client-side programming involves executing pages on the browser after delivery.
  • This speeds up interaction and avoids trip to the server for simple functionality.
  • Examples: JavaScript, AJAX.
• Server-side programming executes page on the web server before sending it.
  • This is typically used for interactive websites interfacing with databases.
  • Tasks involve retrieving shopping categories based on customer preferences and applying business logic.
  • Examples: PHP, Servlet, JSP.

Web Servers

• A web server processes and responds to client requests.
• It hosts websites and includes other servers for gaming, storage, FTP, and email.
• The term web server refers to the entire system or software supervising HTTP requests/responses, like Apache HTTP Server.
• Processing a static web page:
  1. A user enters a URL or clicks a hyperlink using a browser.
  2. The browser translates the action into an HTTP request for the web page after establishing a TCP connection.
  3. The server fetches the web page and sends it to the browser as an HTTP response.
  4. The browser parses the HTTP response and displays the result.

Application Servers

• Application Server (AS) or Web Application Server (WAS) expands web server functionality.
  • Static data (HTML, CSS, Image) goes to the web server.
  • Dynamic data (User's data, Application logic) goes to the AS (or WAS).
• Core features: Process management, load balance, failure recovery, system expansion, database support, security.
• It provides an efficient solution for implementing business logic (e.g., Tomcat, IBM's Web Sphere, Oracle Web Logic Server).
• Types of Application Server Architectures:
  • Three-layer AS architecture suits large-scale web applications, though many server layers can increase system overhead.
  • Two-layer AS architecture, having app server within a web server, for most applications.

Apache HTTP and Tomcat Servers

• Apache HTTP Server is often referred to as Apache Web Server.
  • It is a robust web server that serves static content and is suitable for simple static websites.
• Apache Tomcat is an application server and open-source Servlet/JSP container implementing Java enterprise specifications.
  • It supports Servlets, JSP, and other Java-based technologies.
  • It handles dynamic web applications, executing Java code on the server side, and has its primary strength in dynamic content.
• Tomcat Server is a combination of Apache HTTP Server and Apache Tomcat.
  • The combination allows efficient handling of both static and dynamic content.

Steps For Processing

• Steps for processing a dynamic web page:
  1. A user enters a URL in a browser.
  2. The browser translates the user's action into an HTTP request.
  3. The server retrieves the HTML and sends it to the browser as an HTTP response.
  4. The browser parses the response and displays the user interface.
  5. The user fills the interface, and the browser requests the server to process the data using an HTTP request.
  6. The web server initiates a web program and passes its data.
  7. The web program processes the data and sends the result back to the server.
  8. The web server sends the result to the client with an HTTP response.
  9. The browser parses the HTTP response and displays the result.