SUBJECT DIRECTORY
For general, research oriented queries, and when you want to view sites often recommended
by experts, use a subject directory.
Definition: A subject directory is a service that offers a collection of links to Internet resources submitted by site creators or evaluators and organized into subject categories. Directory services use selection criteria for choosing links to include, though the selectivity varies among services. Most directories are searchable.
When using subject directories, keep in mind that:
INFOMINE, from the University of California, is a good example of an academic subject directory. Yahoo! is a good example of a commercial portal--but it should never be used for serious research. A more complete list of both types of directories may be found on the page Internet Subject Directories.
SEARCH ENGINE
For targeted, complex, and sometimes general queries, use a search engine.
Definition: A search engine is a searchable database of Internet files collected by a computer program (called a wanderer, crawler, robot, worm, spider). Indexing is created from the collected files, e.g., title, full text, size, URL, etc. There is no selection criteria for the collection of files, though evaluation can be applied to the ranking of results.
A search engine might well be called a search engine service or a search service. As such, it consists of three components:
HotBot is a good example of a search engine. A more complete list may be found on the page Internet Search Engines.
DEEP WEB
For targeted queries, when you are looking for non-textual information, use the DEEP WEB.
Definition: The deep Web consists of information stored in searchable databases mounted on the Web. Information stored in these databases is accessible by user query. These databases usually search a targeted topic or aspect of a topic, though entire Web sites may be contained within a database. Search engine spiders cannot or will not index this information.
The deep Web also consists of multimedia and image files, and files created in non-standard file types such as Portable Document Format (PDF). Many search services offer separate search options for locating these files. AltaVista, Excite, HotBot and Lycos are just a few examples of services that offer specialized media searches, while Google integrates searches of PDF files into its general search service.
When dealing with the deep Web, keep in mind that:
In AltaVista, a search on the words
birds migration
means that you will get back documents that contain either the word birds, the word migration, or both. The space between the words defaults to the Boolean OR. This is probably not what you want for this search.
In Google, HotBot Northern Light, a search on the words
birds migration
means that you will get back documents that contain both the words birds and migration. The space between the words defaults to the Boolean AND. This is more appropriate.
Be sure you know the default syntax of the search engine you are using. For an overview of the default syntax of major search engines, see Quick Reference Guide to Search Engine Syntax.
A more detailed look at second generation search services may be found in the tutorial Second Generation Searching on the Web.
There are two types of meta search engines:
Laura Cohen | September 2001
lcohen@albany.edu