Lecture 1 - Introduction.pptx
- 1. Fundamentals of Web Engineering Lecture 1 – Introduction Arsal Mahmood
- 2. Accessing a Website Client computer Server computer Internet connection Web browser Web server Database server
- 3. Components of a Web Application • Web applications are a type of client/server application • In a client/server application, a user at a client computer accesses resources on a server computer • For a web application, the client and server computers are connected via the Internet. • Web browser provides the user interface for the application • Web applications run on a server computer under the control of web server software (IIS or Apache)
- 4. Web Server • A computer program that is responsible for accepting HTTP requests from clients (user agents such as web browsers), and serving them HTTP responses along with optional data contents, which usually are web pages such as HTML documents and linked objects (images, etc.).
- 5. Static Websites • “Static” – the contents don’t change (unless they’re edited). • Web pages (text files) and other needed files (e.g. images) are stored as files on the web server and are retrieved as needed in response to HTTP requests Client Server Browser Web server HTML file HTTP request HTTP response
- 6. Dynamic Websites • Does not have web pages stored on the server in the same form as the user will view them. Instead, the web page content changes automatically and/or frequently based on certain criteria. • The main purpose behind a dynamic website is that it is much simpler to maintain a few web pages plus a database than it is to build and update hundreds or thousands of individual web pages and links.
- 7. Dynamic Websites • There are two ways to create dynamic web pages: • Use client-side scripting to change interface behaviors within a specific web page, in response to mouse or keyboard actions or at specified timing events. In this case the dynamic behavior occurs within the presentation (JavaScript , VBScript & ActionScript), • Use server-side scripting to change the supplied page source between pages, adjusting the sequence or reload of the web pages or web content supplied to the browser. Server responses may be determined by such conditions as data in a posted HTML form, parameters in the URL, the type of browser being used, the passage of time, or a database or server state (PHP, Perl, ASP ASP.NET, JSP). • The documents produced by server-side scripts may, of course, contain client-side scripts.
- 8. Web Browser • A Web browser is a software application which enables a user to display and interact with text, images, videos, music, games and other information typically located on a Web page at a Web site on the World Wide Web. • Text and images on a Web page can contain hyperlinks to other Web pages at the same or different Web site. • Web browsers allow a user to quickly and easily access information provided on many Web pages at many Web sites by traversing these links. • Web browsers format HTML information for display, so the appearance of a Web page may differ between browsers. • Internet Explorer, Opera, Mozilla Firefox, Google Chrome
- 9. Brower - Server communications Type the URL in the web browser. If the URL contains a domain name, the browser first connects to a domain name server and retrieves the corresponding IP address for the web server. The web browser connects to the web server and sends an HTTP request (via the protocol stack) for the desired web page. The web server receives the request and checks for the desired page. If the page exists, the web server sends it. If the server cannot find the requested page, it will send an HTTP 404 error message. (404 means 'Page Not Found')
- 10. Brower - Server Communications The web browser receives the page back and the connection is closed. The browser then parses through the page and looks for other page elements it needs to complete the web page. These usually include images, applets, etc. For each element needed, the browser makes additional connections and HTTP requests to the server for each element. When the browser has finished loading all images, applets, etc. the page will be completely loaded in the browser window.
- 11. Universal Resource Location (URL) http://lms.ntu.edu.pk/moodle/course/view.php?id=146 Protocol (Scheme)
- 12. Universal Resource Location (URL) Host Name http:// lms.ntu.edu.pk/moodle/course/view.php?id=146
- 13. Universal Resource Location (URL) Port No ?!??! http:// lms.ntu.edu.pk/moodle/course/view.php?id=146 HTTP -> port 80 HTTPS -> port 443
- 14. Universal Resource Location (URL) Path http://lms.ntu.edu.pk/moodle/course/view.php?id=146
- 15. Domain Names and Address Resolution • To connect from computer A to computer B an IP address is used • Usually people do not use IP addresses directly to access other computers • As a rule names like www.ntu.edu.pk are used because they are easier to remember • Domain Name Service or DNS distributed database is used to map names to IP addresses
- 16. DNS: Domain Name Service • DNS is a distributed database of computers’ names and their corresponding IP addresses • DNS servers are used to host the DNS database and software to use it • Since the DNS database is too large to be stored on any specific computer only a subset of the database is usually kept on any DNS server
- 17. Name IP Address • The job of the DNS server is to map the name to an IP address • If the DNS server can not resolve the domain request (because it does not have it in its part of the database) then it redirects the request to a different DNS server
- 18. Hypertext Transfer Protocol (HTTP) • HTTP is a request/response standard of a client and a server. • The client making a HTTP request—using a web browser, spider, or other end-user tool—is referred to as the user agent. • The responding server—which stores or creates resources such as HTML files and images—is called the origin server. • HTTP is a connectionless text based protocol.
- 19. Hypertext Markup Language (HTML) • It provides a means to describe the structure of text-based information in a document—by denoting certain text as links, headings, paragraphs, lists, etc.—and to supplement that text with interactive forms, embedded images, and other objects. • HTML is written in the form of "tags" that are surrounded by angle brackets. • HTML can also describe, to some degree, the appearance and semantics of a document, and can include embedded scripting language code (such as JavaScript) that can affect the behavior of Web browsers and other HTML processors.
- 20. Interesting Stuff to Study • Browser Plug-ins • Cookies
Editor's Notes
- #6: A static website is one that has web pages stored on the server in the same form as the user will view them. It is primarily coded in HTML (Hyper-text Markup Language). A static website is also called a classic website, a five-page website or a brochure website because it simply presents pre-defined information to the user. It may include information about a company and its products and services via text, photos, Flash animation, audio/video and interactive menus and navigation. This type of website usually displays the same information to all visitors, thus the information is static. Similar to handing out a printed brochure to customers or clients, a static website will generally provide consistent, standard information for an extended period of time. Although the website owner may make updates periodically, it is a manual process to edit the text, photos and other content and may require basic website design skills and software.
- #7: In one way, a data-driven website is similar to a static site because the information that is presented on the site is still limited to what the website owner has allowed to be stored in the database (data entered by the owner and/or input by users and approved by the owner). The advantage is that there is usually a lot more information stored in a database and made available to users.