Tonga Institute of Higher Education IT 141: Information Systems Lecture 10: The World Wide Web

Outline In this chapter, you will learn about: The World Wide Web HTML HTTP and HTTPS protocols Web browsers and servers Cookies Scripting languages and Java applets Security

The World Wide Web In 1991, Tim Berners-Lee created a protocol to provide a way for documents to be viewed over a network This was the beginning of the World Wide Web The WWW is not the same as the Internet. The WWW is a popular service that is offered over the network of computers called the Internet The Internet is a collection of wires and computers connected together that send many types of data between each other

Hypertext The advantage of viewing documents on the computer allowed for the introduction of hypertext Hypertext is a way to turn normal text into links that allow the user to click through to other documents. The other documents may contain more information. This was an evolution in the history of the written word. Anytime you click on a link in a web browser, you are using hypertext to connect to another place

HTML Hypertext Markup Language is the programming language used to create websites It adds in extra data to a normal text file that changes the formatting of the document. A web server will store one or more webpages, which make up a website. Each webpage is an HTML document that is stored on the server as a file.

HTTP When you request a webpage from a server, your web browser uses a protocol called HTTP to transfer the webpage. HTTP – Hyper Text Transfer Protocol. You will notice all the websites in your browser start with this. It is a protocol that uses TCP/IP to transfer HTML pages

HTTP

HTML – Introduction HTML is called a markup language because people can insert special commands into documents to change the way the documents appear These special instructions are called HTML tags Tags are commands enclosed by brackets, Examples <BR> <HR> <B> <I> You will not see the tag on your web browser, but instead you will see what it changes

HTML HTML tags usually work in pairs. This means that if you want something to be BOLD, you would put <b>Word to make bold</b> You start a tag with the brackets and the command You end the tag with a ‘/’ before the command These types of tags will modify the way the web page appears If you want the modification to end you must have the end tag.

HTML documents HTML documents look different from webpages. A web browser will “render” an HTML document into what you see on the web browser. This “rendering” is like compiling, except you can still see the source code by right-clicking on a page and going to “View Source”

Web Browsers Your browser is what lets you see a webpage. It will do two things: 1. Send a HTTP request for a webpage 2. Render an HTML document The first browser was called Mosaic, made in 1993 Today there are many good browsers available. Examples: 1. Internet Explorer (90% market share) 2. Mozilla/Firefox (8% market share) 3. Opera (1% market share)

How does HTTP work HTTP is a TCP/IP protocol because you need to establish a connection with the web server and your computer before data is successfully exchanged. HTTP uses simple commands to request information and also to send information back to a web server One common command is “GET”, and it allows web browsers to retrieve a web page from a server To test this, you can connect to a webserver without your browser and then try to "speak" the HTTP protocol On Windows computers, go to Start -> Run and type telnet www.tihe.org 80 A connection will be established with the web server and then type GET / This command will get the main webpage of the www.tihe.org What do you see when you type this?

Web Servers A web server is a program that waits for HTTP connections to be made When a connection is made it reads the HTTP request to see what is wanted and then sends back the correct file Web servers can do many requests at the same time, but for really big web sites, like yahoo.com, they need many hundreds of computer to all act as server Is a web server the same as a website? No! Sometimes a web server will have more than one website on it

Cookies After the first few years of using HTTP, people realized the need for websites to be able to save information on the user's computer and then later retrieve it. For example: to remember passwords, help with user authentication, save shopping carts, etc. Cookies are small files that are saved on your computer by websites. They allow websites to "remember" you over a period of time To view the cookies for Internet Explorer, go to C:\Documents and Settings\<username>\Cookies

Cookies Whenever data is exchanged over a network, there is a possibility that one end of the connection may try to send or get data that they are not meant to get Cookies could potentially be dangerous to a user if, for example, your username and password for your bank account was saved in a cookie and then a webserver owned by a hacker could read that username and password Web browsers are responsible for limiting who is allowed to access cookies. A website cannot read cookies that it did not make If yahoo.com leaves a cookie on your computer, microsoft.com cannot read it or use it even if you go to the website microsoft.com Some cookies on your computer forever, some will delete after you close the browser. It depends on what the website does.

Beyond HTML HTML is good for formatting webpages, but many people wanted more power to display and design webpages. DHTML – Dynamic HTML – A language that allows extra functionality in HTML. It is not a replacement for HTML, but an addition, to make HTML do more exciting things Flash – a way to create animated displays with sound in a way that does not create very large files. (Large files take a long time to download on the Internet).

Javascript and VBScript Scripts are ways to add programming to a webpage. HTML is sort of like a programming language, but differs in some important ways. HTML is a Markup Language JavaScript and VBScript are programming languages that allow logic to be inserted into the way a webpage operates For example, they are often used to make sure you are entering correct information into forms. If you go to the Web Email on www.tihe.org, and press Login without typing a password, a message will appear that tells you do type in a password. This is JavaScript in action.

Client Side Scripts Javascript and VBScript are called client-side scripts, because the clients computer (or web browser) runs the program. Your web browser downloads the source code for these programs (often they are included in the HTML file) Your browser is then responsible for compiling the code and executing it within the web browser

Server Side Scripts Server-side scripts are programs that run on the server, instead of the client. A web browser will request a webpage and the webserver may notice that there is programming within the webpage. The webserver will compile and execute the code and then send an HTML page back to the user. The web browser never even seen the source code of the scripts, unlike client-side scripts. WebEmail is an example of server side scripting. Notice, when you login the email displayed is different from another person’s email. There is a script on the server that changes what email is displayed based on the username and password entered Some scripting languages: PHP, Perl, ASP or ColdFusion. (The web email at tihe.org uses PHP)

Java applets Java is a real programming language and it needs to be compiled before you can use it. Scripts are different in that you can execute a script without compiling before. Java applets are Java programs made for webpages. They are a useful way for adding programs that may display graphics and request user input at the same time

The way Java applets work

Security on the Internet When you make a request for a webpage over the internet, if it is uses the HTTP protocol, it is called unsafe or unsecure. It is unsecure because the data is sent unencrypted (or in plain text) over the Internet For most webpages this is not important, but if the web page you go to asks for your username and password, you don't want other people to see it How do other people see it? When your data travels over the Internet it must go through many different computers. Each computer it goes through provides an opportunity for the person/company who owns the computer to look at the data

Security on the Internet There is a secure protocol called HTTPS (the extra S is for secure). This encrypts data between you and the server Encryption is a way to turn normal text into a form that is almost impossible to turn back unless you know the secret password. If you enter important information about yourself on a webpage, make sure it says HTTPS in the URL (the place where you type the name of the website)

Summary The World Wide Web (WWW) HTML HTTP and HTTPS protocols Web browsers and servers Cookies Scripting languages and Java applets Security