1. Information Retrieval and Web Design
Lecture (2)
Prepared by
Dr. Dunia Hamid Hameed

2. Browsers
Browsers are computer programs that read HTML documents and display them accordingly, such as the popular browsers Microsoft Internet Explorer and Netscape Communicator. These programs are clients that connect to web servers that hold actual web documents and send those documents to the browsers by request.

3. URL
Each web document has a web address called the URL (Universal Resource Locator) that identifies it uniquely. The URL is used by browsers to request documents from servers and in hyperlinks as a reference to other web documents. Web documents associated with their web addresses (URLs) are usually called web pages.

4. URL Segments A URL consists of three segments and has the format
<protocol name>://<machine name>/<file name>,
where <protocol name> is the protocol (a language for exchanging information) that the browser and the server use to communicate (HTTP, FTP, etc.), <machine name> is the name (the web address) of the server, and <file name> is the directory path showing where the document is stored on the server. For example, the URL

5. Entering the URL in the address window makes the browser connect to the web server with the corresponding name using the Hyper Text Transport Protocol (HTTP).

6. DNS
After a successful connection, the HTML document is fetched and its content is shown in the browser window. Some intermediate steps are taking place meanwhile, such as obtaining the server Internet address (called the IP address) from a domain name server (DNS), establishing a connection with the server, and exchanging commands.

7. Formally, the Web can be seen as a directed graph, where the nodes are web pages and the links are represented by URLs. Given a web page P, the URLs in it are called outlinks. Those in other pages pointing to P are called inlinks (or backlinks).