Search Tools and Search Engines

Searching for Information and common found internet file types

Search Tools

• Directories are lists of web sites classified by topic. They are created by people submitting web pages to a group of other people who classify and index them. E.g. Yahoo

• Search engines allow one to find specific documents through keyword searches or menu choices. They find web pages one their own. Search engines use software indexers called spiders to crawl around the web and build indexes based on what they find. E.g. altavista, lycos etc.

• Search engines can be classified as either general or specialty search engines. A general search engine retrieves information from a database that contains information on a wide variety of topics

• Specialty search engine is also called a vertical search engine or a topic search engine. Its database contains information on a specific topic. It provides an in-depth information

• Metasearch engine or all-in-one search engine performs a search by calling on more than one other search engine to do the actual work. It does not maintain its own database of information

• Examples dogpile, metasearch

• White pages provide one with a on-line mechanism for looking up information about individuals. They can be used to track down telephone numbers, s-mail addresses, and email addresses. Examples, whowhere, bigfoot

Search Terminology

• Search tool: any mechanism for locating information on the web; usually refers to a search or metasearch engine, or a directory

• Query: information entered into a form on a search engine’s web page that describes the information being sought. Note that a query is not usually phrased as a question

• Query syntax: a set of rules describing what constitutes a legal query. On some search engines

Search Terminology

• Query semantics: a set of rules that defines the meaning of a query

• Hit: a URL that a search engine returns in response to a query

• Match: a synonym for hit• Relevancy score: a value that indicates how close a

match a URL was to a query; usually expressed as a value from 1 to 100, with the higher score meaning more relevant.

Search Engine Components

• User Interface: the screen in which you type a query and which displays the search results

• Searcher: the part that searches a database for information to match your query

• Evaluator: the function that assigns relevancy scores to the information retrieved

Search Engines Database

• Gatherer: the component that traverses the web, collecting information about pages

• Indexer: the function that categorises the data obtained by the gatherer and creates the index

Searcher

• The searcher is a program that uses the search engine’s index and database to see if any matches can be found for the query. The query must first be transformed into a syntax that the searcher can process.

• Evaluator– The hits retrieved by your query are called the

result set of the search.

Gatherer

• A program that traverses the web and collects information about web documents. Other names for the gatherer are bot, crawler, robot, spider and worm.

• Breadth first and depth first