Chapter 7 Notes - The Web and E-mail

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Computer Science
Igor Ivkovic

Chapter 7: The Web and E-mail CP102 Midterm #2 Notes History: 1990 ▯Tim Berners-Lee developed specifications for URLs, HTML, and HTTP (a group of technologies designed to help researchers share info by creating access to a “web of electronic documents” 1991▯Lee’s free Web Software available on Internet 1993 ▯ Web took off in 1993, when MarcAndreessen created Mosaic Web Basics • Web = World Wide Web, collection of document, image, video, and sound files that can be linked/access over Internet using protocol called HTTP • Concept of interlinking documents to access them predates to 1945▯Vannevar Bush; microfilm-based machine called Memex that linked associated info or ideas through “trails” • 1960▯ idea of interlinked documents resurfaced by Ted Nelson▯ “hypertext” a term used to describe a computer system that stores literary documents, links them according to logical relationships and allows readers to comment and annotate what they read • Web 2.0=group of new and innovative ways to use web eg. For social networking, blogging, wikis • Web 3.0=group of technologies like cloud computing • Website= contains collection related info organized/formatted so can be accessed using “browser” • Web server= internet-based computer, accepts requests from browsers, collects requested info and transmits back in a format that can be displayed on webpages • Web page= product/output of one or more web-based files (has vidoes,sounds,interactive elements) • Main tool to access web pages = browser software (microsoft internet explorer, open-source Firefox, Google Chrome, Safari) • Web browser= client software that displays web page elements and handles links b/w pages • Hypertext link = on browser, use this link to access the web page (an underlined link that opens a webpage) • URL = a type of URI ▯ uniform resource identifier (other types of URIs = Social Security #’s, ISBN’s); each web page has unique URL (Uniform Resource Locator), when you type it http:// can be omitted; file name of specific web page always appears LAST in URL; web page file names extensions are usually▯ .htm or .html (hypertext markup language) o o ^web protocol standard ^foldername o URL for a Web Page indicates the computer on which it is stored, its location on the Web server, its file name, and its extension. • Home page = main page of web page • Rules for typing URL: o 1. No spaces ever (underline symbol __ used to give appearance of space) o 2. Always use forward slash / o 3. Duplicate capitalization exactly • HTML = hypertext markup language; set of specifications to create documents that a browser can display as a web page (uses markup language and HTML tags ▯ special instructions) o Tim Berners-Lee developed original HTML specif. in 1990 o Current version (2010) ▯ HTML5 • XHTML = markup language similar to HTML, but customized with tags that describe data in databases o More rigidly structured than HTML, have to adhere to syntax rules • HTML document= (contains text and HTML tags) doc that has .htm or .html extension, and html tags , and which are instructions for browser • Source document = another name for HTML document because it is the source of HTML tags used to construct web page • HTTP = protocol that works with TCP/IP to get resources to your desktop (any chunk of data with a URL like an HTML document, graphic or sound file) o Includes commands called “methods” so browser can communicate with web servers o GET most frequently used HTTP method ▯ GET method used to retrieve text and graphics files imp. to display webpage or to pass a search query to a file server o HTTP transports your browser’s request for a Web resource to ▯ web server ▯ and then transfers web severs response back to -▯ browser • HTTP exchange takes place over pair of sockets = abstract concept that represents one end of a connection o For HTTP, sockets associated with port 80 on client and server o HTTP messages flow b/w a browser and a web server o In an HTTP exchange = browser opens a socket on your PC, connects to a similar open socket at web server, and issues a command like “send me an HTML document” ▯ server receives command, executes it, and sends response back via socket • Persistent HTTP connection= reuses same HTTP connection to send and receive multiple requests (used todays age) • HTTP Status code = a web server’s response to browser’s requests that indicates whether request could be fulfilled o 404 not found – error message (says that requested source does not exist) • web cache = temporary files stored when your browser fetches graphics to form a web page, comes in handy when you switch back and forth between pages or sites • popular browsers: Netscape Navigator (one of the first with a graphical user interface), Firefox, IE, Safari, Chrome o Firefox – gained popularity 2004 o IE – formed from Spyglass o Safari – 2003 o Chrome – 2008 developed, has best support for HTML5 • Why upgrade browser to new versions: 1) new HTML features won’t be supported otherwise, 2) Web page wont show errors but you wont see all effects, 3) increased security from hackers • Player = term used for plug-ins or standalone software likeAdobe Flash • Plug-in = program that extends a browser’s ability to work with file formats; process of installing a plug-in app creates an association b/w browser and file format like PDF, SWF, MOV (whenever your browser encounters these file formats, it automatically runs plug-in) • Cookie = small chunk of data generated by a Web server and stored in a text file on your computer’s hard disk; allow web site to store info on client computer for later retrieval o Websites use cookies to  1. Track pages you viewed/items you bought  2. Gather info for ad banners to show you  3. Collect personal info, retain for next time you visit site • Cookie is a solution for problems caused by stateless protocol = which maintains NO record of the pages you visited, so each time you connect to a new web page at site, its regarded as NEW VISIT • Cookie made up of: 1) info collected by host site like customer number, 2) web page URL , 3) shopping cart #, 4) access date • how cookies work: browser connects to site that uses cookies, receives HTTP “Set-Cookie” message from web server. The cookie message contains info that your browser stores on your computer’s hard disk. The server that creates a cookie can request it any time your browser is accessing a web page from the website server. • How long cookie stays on computer: when cookie reaches end of its predefined lifetime, the info on it gets erased BUY some cookies have no expiration date or expire in a date into future (these ones accumulate on ur hard disk) • HTML conversion utility: adds HTML tags to a document, spreadsheet, or other text-based file to create an HTML document that can be displayed by a browser • Tools used to create Web Pages o 1) HTML conversion utility: adds HTML tags to a document, spreadsheet, or other text-based file to create an HTML document that can be displayed by a browser (eg. Can work with MS Word to create DOCX file and then use Word’s SaveAs Web Page option to convert doc into HTML format) o 2) using web hosting sites that offer premade templates (just click drag drop) o 3) using special category software called Web authoring software or HTML editors (eg. Dreamweaver, KompoZer, Amaya) • Can use text editor like Notepad (windows) or TextEdit (mac) to create simple HTML docs. IMP to take care of necessary quotation marks and brackets. • Framework of HTML document: o 1.head ▯ HTML doc begins with , and the head Is denoted by tags, contains info that defines global properties o 2. Body ▯ begins with tag, and contains HTML tags that format graphics, sounds, videos HTML TAG USE How to get webpages on Internet: Bold/italiciz e 1. test each page locally Change 2. transfer pages to a webserver .. font size 3. test all pages and links Include Interactive web pages = web pages are interactive eg. Online courses, cloud based horizontal apps, flash ads. Made possible when programming and scripting technologies line supplement native HTML features, such as forms and canvas. Line break Paragraph break HTML form = uses the
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