Search Engines:

• built by computer robot programs ("spiders") -- not by human selection
  
• NOT organized by subject categories -- all pages are ranked by a computer algorithm
  
• contain full-text (every word) of the web pages they link to -- you find pages by matching words in the pages you want
  
• huge and often retrieve a lot of information -- for complex searches use ones that allow you to search within results (sub searching)
  
• UNevaluated -- contain the good, the bad, and the ugly -- YOU must evaluate everything you find

WARNING: The idea of meta-searching is much better than the reality. You would think you would save a lot of time by searching only in one place and sparing the need to use and learn several separate search engines. In fact, that is what people claim. But, in truth, meta-searchers offer a quick and dirty approach to searching that sometimes works. I no longer recommend meta-search engines in any step of a good search strategy. Take a look at these drawbacks to them:

• Most of them dumbly pass your search terms on, without any concern to what happens to your carefully place " " or AND, OR or AND NOT, let alone your NEAR or you + or -. Ixquick and ProFusion handle complex searches intelligently. (New Vivissimo claims to offer this feature, but it often fails unpredictably. I like Vivissimo's subject breakdown in results.) While top-rated SurfWax passes searches through rather simply, it provides such great tools for mining results that all you need is simple searches to start with.
  
• If you search does not get what you want, you do not have the ability to refine your search as you in what I consider the most powerful search engines around (Google, AltaVista Advanced Search and Northern Light). All you can do is add a term and wonder where the meta-search engine is sending it.
  
• None of the meta-search engines consistently queries all of the search engine it claims to query, and you don't know for sure what it is querying until you read the results. If you use ProFusion's advanced search, you have the best control available.

• built by human selection -- not by computers or robot programs
  organized into subject categories, classification of pages by subjects -- subjects not standardized and vary according to the scope of each directory
  
• NEVER contain full-text of the web pages they link to -- you can only search what you can see (titles, descriptions, subject categories, etc.) -- use broad or general terms
  
• small and specialized to large, but smaller than most search engines -- huge range in size
  
• often carefully evaluated and annotated (but not always!!)

• Defined: Pages that cannot be found in search engines and rarely are in subject directories -- the "visible web" is what you can see using these tools -- Invsible Web is estimated to offer two to three times as many pages as the visible web.
• WHY? There are many specialized searchable databases that the World Wide Web allows you to access through a search box in a web page (for example, the UCB Library Catalog Pathfinder, or any other library catalog; or some statistics databases searchable on the web). The terms you use in your search are sent into that specialized database, and are returned to you in another web page that is dynamically generated for your answer. It is not retained anywhere after your search.
  
  • Search Engines cannot access such dynamically generated pages because the computer robots or spiders that build them cannot type the searches needed to generate the pages. Spiders find pages by visiting all the links in the pages they "know about." Unless there are links somewhere that the spiders can use to re-generate specialized database searches, the contents of the database is beyond them. Pages requiring passwords to access them are also closed to search engines, because spiders cannot type. (There are a few other types of pages that most search engines refuse to include; please see the discussion on the Invisible Web page.)
    
  • Directories rarely have the contents of these pages, but, since directories are built by humans capable of typing, there is no reason directories cannot contain links which, if clicked, would cause a search in the database to be dynamically generated each time it is clicked.

Because of their inefficiency and often haphazard and frustrating results, we do not recommend either of the following two approaches to finding Web documents:

• Browsing searchable directories. If you can find a search box, search a directory. BROWSING is a sometimes fun rarely as efficient. The term "directories" refers here to any collection of web resources organized into subject categories or some other breakdown appropriate to the content (Subject Directories or directories of specialized databases or of gateway pages). Browsing locates documents by your trying to match your topic in first the top, broadest layer of a subject hierarchy, then by choosing narrower sub-subject-categories in the hierarchy that you hope will lead to your target. Browsing encounters the difficulty of guessing under which subject category your topic is classified. The taxonomy in every directory differs, making browsing inconsistent from one search tool to another. The category "health" may contain documents on medicine, homeopathy, psychiatry, and fitness in one directory. In another "medicine" may include health, mental health, and alternative medicine, but not the term psychiatry and may classify fitness only under "lifestyle." Searching (typing keywords in a search box) retrieves occurrences of your words no matter where they may be classified by subject. Use broad terms in searching any directory.
  
• Following links to sites recommended by heavy use or commercial interest.  Often in search engine results, you will see links to sites that are selected based on how often they are visited by others, or based on fees paid to the browser.  Or you may see recommended "cool" sites.  Use these with caution!   Others may visit sites for reasons having no relation to your information interests, and the best sites for you may still be largely undiscovered by the vast public searching the Web.  Taste varies and should vary.  Make your own evaluations.