Outline of Class 4: Organizing and Representing Information; HTML

Held: Thursday, January 29, 1998

Administrivia

• I still haven't graded your assignments (or it's likely that I won't have graded assignments at the time I wrote this). Hopefully, I'll get them done by Tuesday.
• Today's assignment: computing assignment 3.
• We'll spend most of today on the computers. Since computers are malicious, prepare for some problems, but don't let them bother you.

Data vs. Algorithms

• Much of computer science is concerned with the algorithms we write.
• However, it is also important how we represent and structure data.
• What is meaningful and readable to the human may be difficult for the computer, and vice versa.
• In addition, the way in which we organize data can significantly affect the algorithms we write. For example, it is much easier to find a word in a sorted list than an unsorted list.
• Hence, part of our study of computing will be a study of data representation.

About Markup Languages

• As you may have observed while playing with a variety of web pages (and other types of computer documents), there is much more to an electronic document than just the contents of the document.
• Some of the "extra" stuff includes
  • Formatting of the text
  • Images
  • Hypertext links
  • ...
• How does the computer remember what everything is?
  • With an internal representation of the text that includes information on all of these other details.
• Often, this representation is helped by a set of "standard" pieces of information, such as the appearance of fonts.
• How can we tell the computer about all of these components?
  • Interactively, using a program that permits us to specify the various issues.
  • Formally, by annotating (or "marking up") the text with information on these extra facets.
• The languages used to annotate texts are called markup languages.
• There are two primary trends in markup: physical markup and logical markup.
• In physical markup you indicate the appearance of each piece of text. For example, the following describes a particular piece of text (but not necessarily itself).

  "This text should be displayed in Helvetica, Italic, Medium Weight, 12 pt. It should be indented one inch from the left margin and one inch from the right margin. It should be separated from the previous text by 1/10 inch. And so on and so forth."

  Obviously, many of these facets can be set for the whole document or automatically guessed.
• In logical markup you indicate the role of each piece of text. For example,

  "This is a quotation."

  The choice of how to format each type of text is then left to the reader/computer/browser/.
• There are a number of arguments for each type of markup.
• Advocates of physical markup claim that
  • There is a wide variety of literature describing the effects of design on readability. Without physical markup, it is much more difficult to produce appropriate designs.
  • In many arenas, the appearance of your text is as important as what you say and how you say it (an extension of the old "what you say is not as important as how you say it").
• Advocates of logical markup claim that
  • Logical markup supports more intelligent document retrieval.
  • Logical markup permits different readers to read documents in a way that makes more sense to them. This includes simple concepts, like which font to use.
  • Logical markup better supports visually-impaired readers, as the computer can be programmed to read different types of text differently (and even to read the type of each piece of text). For example, I've been told that one noted computer scientist has the computer read emphasized text with a James Earl Jones voice.
  • Few authors are good designers; logical markup can separate the two.
• I'll admit that I'm an advocate of logical markup.

About HTML

• HTML, the Hypertext Markup Language, was designed as a simple markup language for documents in the World-Wide Web.
• It originally included both physical and logical markup mechanisms, but only a limited number of each.
• More recently, the web is moving to a clearer relationship between logical and physical markup, with an emphasis on logical markup of documents and accompanying style sheets that provide the physical details.
• One clear goal of HTML is that we should be able to type HTML on any "typical" (or at least "typical U.S.") keyboard.
• How do we mark documents? By using tags to surround pieces of text.
• How do we distinguish tags from regular text? Tim Berners-Lee, the designer of HTML, decided that we'd surround tags with less-than (<) and greater-than (>) signs.
• What are some typical tags? Think about pages and then see the handout.

Work

For today, we'll work on writing HTML, as specified in computing assignment 3.