Deep or Invisible Web Engines & Services
I labored over whether to create this category or not. Deciding that I would, I thought it might be useful to explain my rationale for doing so.
For those unfamiliar with the world of search engines and internet search methodology, there is an entire world of knowledge and resources that Google never tells you about. Google's search results, to the extent anyone knows anything about how it returns its results, are weighted in favor of sites deemed more "popular" than others. "Popularity" in the world of internet search engines means, loosely, that a site has been linked to more often than another site; and theoretically, also takes into account qualitative factors. The end results with Google search, therefore, is that relevancy = popularity.
For example, Google's search results does not take into account whether the person writing an article on, say, a tech blog actually knows anything about technology, writing, blogging or anything else. As long as that individual has lots of link activity associated with them, their site or their article, then Google will return it highly ranked in its search results.
The problem is that such an approach is inherently flawed. Relevancy of results - in a real world sense - depends on numerous factors. Frankly, popularity would not even make my list of such factors. Other search engines, including many that I have pearled, do not function in this manner. They take into account other factors or circumstances, and often will return markedly different search results for the same search query.
One category of knowledge that Google's search results routinely omit is what I would call "academic journals" or "academic databases." Ironically, it is this very data that might prove invaluable to an internet researcher. However, unless you are using Google's well-conceived, though incomplete Scholar database, you are never going to find this information. This information, and many other categories like it, is found by searching the "Invisible Web," or sometimes referred to as the "Deep Web."
A handful of sites claim to specifically search the "Invisible" or "Deep" Web. Some of these sites are operated as private enterprise services aimed at specific industries, and therefore, operate more like discrete databases or clearinghouses, if you will. Others seems to function a bit more like actual search engines.
I elected to create this category as a repository for those sites and services claiming to access the "Invisible" or "Dep" Web. In order to be included, the site or service must have, minimally, met three criteria in my judgment. First, the site or service must maintain a legitimate search technology that is not reliant on any other search provider such as Google, Yahoo or Bing.
Second, when a search query is provided to the site or service, the site or service must do something more than merely search its own pre-set database, regardless of the nature of the database. In other words, the site or service must actually search the "Invisible" or "Deep" Web - or attempt to do so - rather than its own databases. This second criteria is essential for differentiating sites or services that are search engines from the constellation of sites or services that might qualify as "article databases," "document repositories," or "storage and sharing" services.
Third, and finally, sites or services appropriate to this pearltree are not specifically academic ones, such as one might find operated by universities or other learning centers. Obviously, there is the danger of significant overlap here, and I may re-evaluate this criterion as I fill in the pearltree.
I hope this was helpful and informative. Prof. E. Young Mar 25