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Computer Science 101 HTML
World Wide Web • Invented by Tim Berners-Lee at CERN, the European Laboratory for Particle Physics in Geneva, Switzerland (roughly 1989) • Wanted researchers to be able to “link” or cross-reference each others research papers • By mid 1980s we had DNS – domain name service to map domain names to IP address
WWW (cont.) • Berners-Lee developed a simple protocol, HTTP – HyperText Transfer Protocol for exchanging information via hypertext links • The documents themselves were to be marked up using HTML – HyperText Markup Language • HTML based on SGML - Standard Generalized Mark-up Language which was widely used in publishing industry
WWW (cont.) • Early 1990s World Wide Web ramped up • 1993 – NCSA - National Center for Supercomputers (University of Illinois) released Mosaic browser • 1994 – Netscape was formed
Important Web Programs • Web Server: This is a program that manages web sites on server computers. The web server accepts requests from other programs (clients) asking for pages from the web sites. • Browsers: Programs like Internet Explorer and Firefox that act as clients for web servers requesting pages for the user and displaying the returned pages.
HTML • HyperText Markup Language – HTML is used to mark up a document to tell browser how it should be displayed, nothing about content • Allows us to markup up text with special tags that inform the web browsers how the content should be displayed • For the most part HTML tags are placed in “angle brackets” like <b> and occur in pairs like <b> Here is some text </b>
Some HTML tags • html – this tag together with its end tag enclose the entire document • head – there are two sections to the document, the head and the body. For the most part the head section contains the title of the document • title – encloses the page title shown in title bar at the top • body – enclose the body of the document, essentially all of the displayed content
A Minimal HTML document <html> <head> <title> Title of your page </title> </head> <body> All the good stuff goes here </body></html>
More tags • h1 – There are six levels of headings in HTML, numbered h1 through h6 with h1 being the largest and boldest • p – Marks the beginning of a new paragraph. • ul – enclose an unordered list – bullet list • ol – enclose an ordered or numbered list • li – enclose an item in a list
More tags • br – Causes a line break to occur. Does not use an end tag(Recommend: <br/> • hr – Causes a horizontal line to be drawn across the page. No end tag. (Recommend: <hr/>) • b – enclosed text is bold • i – enclosed text is in italics
The anchor tag • The anchor tags, <a> and </a>, are used with links. • To specify a link from a location in your page to a location in current page or another page on the web. • To specify a location in your page that can be linked tofrom another location in the current page or from another page.
Making links – HREF Attribute • General form is<a href = “URL”> link-phrase</a> • URL (Uniform Resource Locator) is the web address to link to • link-phrase is the phrase to appear on your page for the user to click in order to execute the link.
Linking to other places: HREF attribute • Suppose we want to have a link on our page to link to W&L’s home page. The following markup will achieve this:<a href=“http://www.wlu.edu”> My University </a>
Locations that can be linked to:Name attribute • In order to link to specific locations within a page, these locations must first be given names that are recognized by HTML. • To do this we use the anchor tag again, but now using the NAME attribute rather than the HREF attribute.
Linking to locations in same page • General form is<a name = “location-name”> Location-title</a>where location-name is the name that will be used in anchors that link to this location, and Location-title will appear at the position where the Name anchor is placed.
Linking to named locations in same page • Example: <a name=“Ch2”>Chapter 2 – Tree Algorithms</a> • Suppose we put the above tag at the beginning of the Chapter 2 section of our page. Then to link from another location to Chapter 2, we could use any of the following:<a href= “#Ch2”> Chapter 2</a> <a href = “#Ch2”> Tree Algorithms</a> <a href = “#Ch2”> Chapter 2 – Tree Algorithms</a> • Here the # indicates that we are linking to an anchor location within the page.
Linking to named locations in another page • Example: <a name=“Ch2”>Chapter 2 – Tree Algorithms</a> • Suppose the named location above occurs in “MyReport.html” and that we would like to place a link to that location in “MyWork.html”. At the place where we want the link, we could have<a href = “MyWork.html#Ch2”> See Chapter 2 </a>assuming these files are in same location. Otherwise, use the full web address to MyWork.html.
Images • Here is an example for having an image in the file<imgsrc =“TractorRide.jpg”>
Background Color • We can add a background color to our web page by adding a bgcolor attribute to the Body tag: <body bgcolor = “value”> • The value can be either a “known” color or a color specified with the 6 hex digit system.
Background Color (cont.) • There is a long list of “known” colors, but only 16 that are guaranteed to validate with all browsers:aqua, black, blue, fuchsia, gray, green, lime, maroon, navy, olive, purple, red, silver, teal, white, and yellow • To specify a background color with hex digits use the form<body bgcolor = “#D454C8”>for example