Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-WesleyFluency with Information TechnologyThird Editionby Lawrence SnyderChapter 5: Searching for Truth: Locating Information on the WWW5-21-2Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-WesleySearching in All the Right Places• The Obvious and Familiar– To find tax information, ask the tax office• Libraries Online– Many college and public libraries let you access their online catalogs and other information resources• Libraries provide online facilities that are well organized and trustworthy• Remember that many pre-1985 documents are not yet available online• Plus Librarians are real live experts5-31-3Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-WesleyHow Is Information Organized?• Hierarchical classification (like a family tree)• Information is grouped into a small number of categories, each of which is easily described (top-level classification)• Information in each category is divided into subcategories (second-level classifications), and so on• Eventually the classifications become small enough for you to look through the whole category to find the information you need– This is a process of elimination as much as choosing appropriatesubcategories5-41-4Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-WesleyImportant Properties of Classifications• Descriptive terms must cover all the information in the category and be easy for a searcher to apply• Subcategories do not all have to use the same classifications• Information in the category defines how best to classify it• There is no single way to classify information5-51-5Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-WesleyDesign of Hierarchies• General rules for design and terminology of hierarchies– Root is usually at the top (branching metaphor)• "Going up in the hierarchy" means the classifications becomes more inclusive or general• "Going down in the hierarchy" means the classifications become more specific or detailed• The greater-than (>) symbol is a common way to show going down through levels of classification5-61-6Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-WesleyLevels in a Hierarchy• A one-level hierarchy has only one level of "branching"—no subdirectories• To count levels, remember– There is always a root– There are always "leaves"—the categories themselves– The root and leaves do not count as levels• Groupings may overlap (one item can appear in more than one category), or be partitioned (every category appears only once)• Number of levels may differ by category, even in the same hierarchical tree5-71-7Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-WesleyHow Is Web Site Information Organized?• Homepage is the top-level classification for the whole Web site• Classifications are the roots of hierarchies that organize large volumes of similar types of information• Topic clusters are sets of related links– For example, sidebar and top of page navigation links• Content information often fills the rest of a page5-81-8Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley5-91-9Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-WesleySearching the Web for Information• How a Search Engine Works– Two basic parts: 1. Crawler: Visits sites on the Internet, discovering Web pages and building an index to the Web's content2. Query processor: Looks up user-submitted keywords in the index and reports back which Web pages the crawler has found containing those words• Popular Search Engines: Google, Yahoo!, MSN, AOL, Ask5-101-10Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-WesleyCrawlers• When a crawler visits a website:– First identifies all the links to other Web pages on that page– Checks its records to see if it has visited those pages recently– If not, adds them to list of pages to be crawled– Records in an index the keywords used on a page (appear in the title, the body, or in anchor text)• Crawlers can miss pages– No page points to it– Page is dynamically created on-the-fly– Page has only images– Page type is not recognized (not HTML, PDF, etc.)5-111-11Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-WesleyQuery Processors• Gets keywords from user and looks them up in its index• Even if a page has not yet been crawled, it might be reported because it is linked from a page that has been crawled, and the keywords appear in the anchor text on the crawled page• Important to give the right terms to look up5-121-12Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-WesleyPage Ranking• Google's idea: PageRank– Orders links by relevance to user– Relevance is computed by counting the links toa page (the more pages link to a page, the more relevant that page must be)• Each page that links to another page is considered a "vote" for that page• Google also considers whether the "voting page" is itself highly ranked5-131-13Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-WesleyAsking the Right Question• Choosing the right terms and knowing how the search engine will use them• Words or phrases?– Search engines generally consider each word separately– Ask for an exact phrase by placing quotations marks around it• "thai restaurants"5-141-14Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-WesleyLogical Operators• AND, OR, NOT– AND: Tells search engine to return only pages containing both terms (default)Thai AND restaurants– OR: Tell search engine to find pages containing either word, including pages where they both appearThai OR Siam– NOT/-: Excludes pages with the given word-review• AND and OR are infix operators; they go between the terms• NOT/- is a prefix operator; it precedes the term to be excluded• Google Help: Cheat Sheet– http://www.google.com/help/cheatsheet.html5-151-15Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley5-161-16Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-WesleyFive Tips for an Efficient Search1. Be clear about what sort of page you seek (company or organization, reference page, etc.)2. Think about what type of organization might publish the page