1 COMS 161 Introduction to Computing Title: HTTP and HTML Date: October 13, 2004 Lecture Number: 21

2 Announcements Material –Chapter 18 (The Internet) –Chapter 5 (Creating Documents) pp 92 Homework 6 –Due (Friday) 10/15/2004

3 Review Internet Protocols World Wide Web –Client/Server –URL –Web Browser

4 Outline HTML and HTTP

5 URL Example Protocol Domain Name Resource location URL for the book

6 Web Browser (Client) Title bar Menu bar Tool bar

7 Researching on the Web Search service--generates lists of other Web sites containing information about supplied topics Web directory--a search service organized as a topical hierarchy and compiled by (human) editors Search engine--search services whose databases are compiled by automated Web crawlers

8 Keyword Searching A form of (automated) text matching Keyword--a word or phrase used as a text pattern for matching Hits--matches with text patterns Misses--fails to match some or all of the text pattern False positives--hits that are not related to the desired topic

9 Boolean Expressions Search engines interpret multiple keywords as Boolean expressions AND--intersection, i.e., references that contain both keywords

10 Boolean Expressions OR--union, i.e., references that contain either keyword

11 Boolean Expressions NOT--negation, i.e., references that do not contain the keyword

12 Mathematical Operators Boolean ExpressionMathematical Operator Labrador AND retrievers+Labrador +retrievers Labrador AND NOT retrievers +Labrador -retrievers Mathematical operators may be used to signify Boolean expressions

13 Hybrid Search Services Metasearch engines--consult other search engines and directories and summarize query data Niche services--commercial services targeted at a specific audience or topic Portals--gateway Web site with searching capabilities

14 Web Browsers and Servers Web browsers are clients –Request, receive, and display Web documents Web sites are servers –Store Web information –Process browser requests –Send information back to the browser The protocol used is called “HTTP” –Hypertext Transfer Protocol –Method by which browsers and servers communicate

15 Web Publishing HTTP defines how browsers and servers communicate “HTML” is the language they use –Hypertext Markup Language –HTML signifies both content (elements) and structure (presentation) –Content and structure are specified separately

16 Web Publishing HTML -- Hypertext Markup Language –Hypertext Links to variety of information, local or remote –Markup Originally from print publishing: handwritten marks on text to indicate presentation instructions to the typesetter –Text size, bold or italic, headlines vs. body text, column layout, etc. –Language Standardized set of instructions for a computer

17 Web Publishing HTML is designed to be: –Platform independent Any computer, any browser –Resolution independent Any screen or printer size –Multimedia Text, images, video, sound, interactive tools, etc. –Hyperlinked Immediate links to other content, local or remote

18 HTML Plain text with markup tags –Plain text: standard (ASCII) characters –Markup tags: embedded commands (still in plain text) identifying content and structure

19 HTML Tags Not case-sensitive Textbook uses UPPER case; lower is now more common Many tags are “paired tags” Example: This is some sample HTML. Appears as : Tags

20 Basic Document Structure (Signifies an HTML document) (Descriptions of the document go here) (Page content goes here)

21 Setting a Page Title Titles help give the user a frame of reference Titles appear in taskbar and browser’s title bar Example: Hampden-Sydney College, Virginia Appears as:

22 Text in HTML Simple text is in enclosed in paragraph tags Automatically wraps to fit Example: The rain in Spain stays mainly on the plain. Appears as: The rain in Spain stays mainly on the plain.

23 Text in HTML Break tags help to format lines Example: Audrey Hepburn played Eliza Doolittle in the movie version of "My Fair Lady“ even though that role was played by Julie Andrews on stage. Appears as: Audrey Hepburn played Eliza Doolittle in the movie version of "My Fair Lady" even though that role was played by Julie Andrews on stage.

24 Text in HTML Font face, color, style, etc. may be specified Example: Roses are red, violets are blue… Appears as: Roses are red, violets are blue…

25 Text in HTML Some other kinds of text formatting: –Italics This is italic text. This is italic text. –Bold This text is bold. This text is bold. –Underline And this is underlined. And this is underlined. –Superscript Here is a super script. Here is a super script. –Subscript And, here’s a sub script. And, here’s a sub script.

26 Text in HTML Font sizes –Absolute font size: a number between 1 and 7 –Example: A B C Appears as: A B C –Relative font size: use a number like –n or +n (where n is some digit) –Example: X Y Z Appears as: X Y Z –“basefont” size is 3

27 Headings in HTML Headings of different weights are used to introduce sections Example: My Autobiography Part 1: My Early Years Chapter 1: I Am Born It was a dark and stormy night… Appears as: My Autobiography Part 1: My Early Years Chapter 1: I Am Born It was a dark and stormy night …

28 Comments Comments may be added to an HTML file –Information for someone reading the HTML file –Comments do not appear in the browser Example: My Autobiography Part 1: My Early Years Chapter 1: I Am Born It was a dark and stormy night… Appears as: My Autobiography Part 1: My Early Years Chapter 1: I Am Born It was a dark and stormy night …

29 Lists in HTML Three kinds of lists: –Ordered lists (automatically numbered) –Unordered lists (bullet points) –Definition lists (terms and definitions)

30 Ordered Lists Automatically numbered Example: Outline: Introduction Body Conclusions Appendices Appears as: Outline: 1.Introduction 2.Body 3.Conclusions 4.Appendices Is “list item” ( ) a paired or an unpaired tag?

31 Unordered Lists Bullet points Example: HTML has three types of lists: Ordered Unordered Definition Appears as: HTML has three types of lists: Ordered Unordered Definition Exactly the same syntax as ordered lists, except “ ” instead of “ ”

32 Definition Lists Terms and definitions Example: Glossary: HTTP A protocol: the mechanism that computers use to exchange web documents. HTML A language: the terms and symbols used in web documents to define the content and layout of a web page. Appears as: Glossary: HTTP A protocol: the mechanism that computers use to exchange web documents. HTML A language: the terms and symbols used in web documents to define the content and layout of a web page.

33 Inline Graphics Images may be placed on the page along with text and other elements Only standard image formats:. gif,.jpg, a few others Example: Audrey Hepburn played "Eliza Doolittle" in My Fair Lady. Appears as: Audrey Hepburn played "Eliza Doolittle" in My Fair Lady.

34 Hyperlinks The key to the Web Cross references to other elements: pages, images, multimedia, etc. Clicking on a hyperlink causes an automatic request for the linked element Example: Web site for the textbook Exploring the Digital Domain. Appears as: Web siteWeb site for the textbook Exploring the Digital Domain.

35 Web Publishing Tools Text editors (e.g. Notepad) –Create and edit plain text files with HTML tags Tag editors (e.g. Dreamweaver’s “code view”) –Tools that make it easier to place tags in text files HTML generators (e.g. Dreamweaver’s “design view”) –Tools that automatically create HTML codes much like a word processor Site Managers (e.g. Dreamweaver’s “Site” menu) –Help organize and keep track of all files that make up a site HTML files, images, databases, programs, etc. –Assist with keeping files on the server in synch with local files

36 Censorship Why would someone want to censor the Web? Is censorship right? Who decides? How, technically, would one actually control Web content? –Blocking software –PICS ratings –Communications Decency Act (1996–1999) –Other ideas? How does this relate to Spam filters?