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Hyperlinks and URLs and how we access information using them are an integral part of the success of the World Wide Web and Internet as we know it nowadays.

They are simple but powerful concepts. An hyperlink is a reference to some data that the reader can directly follow either by clicking or by hovering. A hyperlink points to a whole document or to a specific element within a document. Hypertext is text with hyperlinks. A user following hyperlinks is said to navigate or browse the hypertext. If a hyperlink is bound to a portion of a document (generally text, though not necessarily), it is called an anchor hyperlink and the text is called anchor text (for example, in the hyperlink represented in the slide the anchor text is Wikipedia)

A uniform resource locator (URL) is a reference to a resource that specifies the location of the resource on a computer network and a mechanism for retrieving it. A URL is a specific type of uniform resource identifier (URI), and many people use both terms interchangeably. URLs occur most commonly to reference web pages (http), but are also used for file transfer (ftp), email (mailto), database access (JDBC), and many other applications.

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Once we have text with links (that we call hypertext) and universal directions (URLs) we need a couple more things: a protocol to transfer it over IP networks and a way to enrich the text that enables us, for example, to format it or to include images, videos and other objects. To send hypertext over IP networks we have the Hypertext Transfer Protocol (HTTP), an application protocol for distributed, collaborative, hypermedia information systems that is the foundation of data communication for the World Wide Web.

HTTP is an unsecure protocol, that transmits hypertext in plain text with no encryption, so HTTPS was developed to improve security, incorporating the use of SSL or TLS protocols for encryption

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To enrich hypertext documents and give them structure, a special markup language was created, HTML, an acronym that stands for Hypertext Markup Language. This is the standard markup language used to create most web pages today and it is now in version 5. As it name says, it is not a programming language, it is a way to mark up the text. It works by wrapping the text in tags enclosed in angle brackets (like ). This tags usually work in pairs (one to signal the start of the section marked and another with a bar to signal the end). With them we can structure the document in different sections (as paragraphs or divs), add headers (with tags), hyperlinks (with the tag), embed other web pages or format sections of text (for example we can use the tag to mark a part of the text as bold). There are also individual tags, as, for example, the one used to embed images ()or the one used to mark a new line


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The World Wide Web Consortium (W3C) is the main international standards organization for the World Wide Web

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WEB PAGE: Single document suitable for the World Wide Web WEB BROWSER: Client software application that presents Web pages to users WEB SITE: set of related web pages typically served from a single web domain WEB SERVER: Computer system that accepts and processes World Wide Web requests

Web server can refer to the whole computer system attending the requests or specifically to the software that accepts and attends them. Sometines the terms web site and web server are used interchangeably, but this is not completely correct, as a big web site can be hosted and attended by several servers that share the network load serving the same content to different users, or that perform different functions depending on users’ requests. PUSH TECHNOLOGY: Term used when a Web site automatically downloads data or files to a computer whenever new data are available or at scheduled intervals

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As we have seen web pages are no more than hypertext documents with a mechanism to embed images, videos and other objects.

These hypertext documents and their related objects are stored in servers called web servers, whose primary function is to store and deliver web pages to clients; these are usually web browsers following the client server model. For a static web page, a web server is a special type of file server that receives a web page request using the HTTP or HTTPS protocol and responds sending with the same protocol the web page file and all the files linked or included in the page. With all these files the web browser interprets the web page and presents the graphic result to the user. If the server is unable to send the content it responds with an error message.

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But, as the World Wide Web started to gain in popularity, it soon became clear that static pages were not enough. There was a lot of information stored in databases that was of interest to users and generating a static HTML page for every user need was impractical and, in some cases, impossible. So a new concept was introduced, dynamic web pages, which are web pages that are generated on the fly from data stored in a database with content that depends on the user’s needs. To generate the html page from the data stored in the database, when the request arrives, the server uses server side scripting, that consists in having installed a programming environment and executing a script that retrieves the data and constructs the web page. The languages generally used for server side scripting are php, python, ruby on rails, perl or asp.net.

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