AddAll is what is known as a MetaSearch Engine.
Wikipedia has a good explanation of just what a MetaSearch Engine is:
"A metasearch engine is a search engine that sends user requests to
several other search engines and returns the results from each one.
They allow users to enter their search criteria only one time and
access several search engines simultaneously. Since no search engine
can catalog the entire web, the idea is that by searching multiple
search engines you are able to search more of the web in less time and
do it with only one click. The ease of use and high probability of
finding the desired page(s) make metasearch engines popular with those
who are willing to weed through the lists of irrelevant 'matches'.
Metasearch engines do not compile databases or catalog the web. They
act as middle-man, taking a user's request and passing it to several
other search engines..."
Read the full entry here:
Joe Barker at UC-Berkeley has created a nice page with more than you'd
ever want to know about MetaSearch Engines:
As far as book selection, both Alibris and Amazon (which are both
searched by AddAll) are tied into a huge cooperative database of
thousands of rare and out-of-print book dealers; that's where that
extra-large number comes from.
You may not realize it, but Amazon.com has itself become a MetaSearch
Engine; when you search on it, some of the stores with inventory
databases accessed include Target, KitchenEtc, Marshall Field's, and
Toys 'R Us.
Since the dot-com collapse, in order to survive, on-line businesses
have frequently resorted to this kind of all-in-one consolidation in
an attempt to get Customers to do all of their shopping, regardless of
the item, at their site.
Many Internet stores such as Amazon, as well as individuals with their
own websites, participate in a "referral" system; where Joe Schmoe has
linked his site to Amazon's Search Engine, if you click on a book
entry, his URL is passed to Amazon, and if you purchase it, he gets a
kickback of a little money for sending business their way:
AddAll is just a big example of a site with referral kickback
arrangements with many different stores.
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