Dogpile web search is powered by Metasearch technology. Dogpile gets its results from other big search engines like Google, Bing, Ask, Yahoo and About.com.
So, basically what Dogpile is doing, instead of getting results from only one search engine, it will receive the best combined search results from all the different search engines. And in addition to Bing, Google, Yahoo and so on, Dogpile also uses some authority sites like Fandango and Kosmix and also some video and audio content providers.
Dogpile creates a virtual database, it does not compile a catalogue of the web or physical database but it take a user's request, pass it to several other databases and then gathers together, filters and organizes the results based on its pacific algorithm.
There are many other search engines besides Dogpile that use metasearch technology.