User Interface Design for Programmers

CHAPTER15But...How DoIt Know?"

Remember the old advertising slogan for Thermoses? They "Keep Hot Drinks Hot and Cold Drinks Cold!" To which your slightly brighter-than-average five-year-old asks: "But...how do it know?"

That's what we in the software design field call a heuristic.Here are a few well-known examples of heuristics:

• If you type the word "teh" in Microsoft Word, Word will decide you probably meant "the" and change it for you.
• If you enter "Monday" into a cell in Microsoft Excel and then drag down, you get the days of the week (see Figure 15-1).
• When you search for text that looks like an address using the Google search engine, it will offer to show you a map of that location.
• If you buy a lot of Danielle Steel books on Amazon.com ...