What’s The Difference??  Subject Directory  Search Engine  Deep Web Search

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.

Search Engine  For targeted, multi-concept, 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.

Deep Web Search  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.  Example: you are looking for a phone number stored in a directory or phone book.

When Should I Use A Subject Directory?  When you have a broad topic or idea to research.  When you want to see a list of sites on your topic often recommended and annotated by experts.  When you want to look around in a controlled environment.  When you want to retrieve a list of sites relevant to your topic, rather than numerous individual pages contained within these sites.  When you want to search for the site title, annotation and (if available) assigned keywords to retrieve relevant material rather than the full text of a document.  When you want to avoid viewing low-content documents that often turn up on search engines.

When Should I Use A Search Engine?  When you have a narrow or obscure topic or idea to research.  When you are looking for a specific site.  When you want to search the full text of millions of pages.  When you want to retrieve a large number of documents on your topic.  When you want to search for particular types of documents, file types, source locations, languages, date last modified, etc..  When you want to take advantage of newer retrieval technologies such as concept clustering, ranking by popularity, link ranking, and so on.

When Should I Use A Deep Web?  When you want dynamically changing content such as the latest news, job postings, available airline flights, etc.  When you want to find information that is normally stored in a database, such as a phone book listing, listings of lawyers, doctors, plants etc., searchable collections of laws, geographical and company data, and so on.

Sample Topics and Hints  Here are some general guidelines regarding how to approach subject directories and search engines as research tools. Begin with a Subject Directory Begin with a Search Engine DisabilitiesAmericans With Disabilities Act Civil WarBattle of Appomattox Space explorationMars Pathfinder British literatureCharles Dickens

Search Results Disclaimer  Some directories and search engines load the top of their results pages with paid listings. These are usually listings of sites whose owners pay for high placement. In other words, they are advertisements.  Not all search services do this, and some are more clear than others about what has been paid for and what has not.

Additional Information  Select a tool for your search:  See handout in the All file entitled “Selecting a Tool for your Search”  Use the links noted on the document entitled “Search Engine Links” in the All file.