Each card contains just information to describe a book and tell you where you can find it on the shelves. So it is with the indexes created by search engines. Each search engine has its own criteria for extracting and indexing information. Some index every single word in a document they find, while others only index 100 key words in each, for example. Some index the size of the document, some index the title, headings, and subheadings, and so on.
Search engines return results in different ways.
Check out their effectiveness by asking each to find the same product or service. As you check the prices MySimon finds, remember to compare the shipping and handling fees as well. Say you're in the market for a digital camera. Productopia will give you three sets of recommendations based on quality, style and value. Then, once you've decided whether you want to be cheap, chic or sensible, Productopia refers you to online and offline vendors.