A web search engine is a software system that is designed to search for information on the World Wide Web. The search results are generally presented in a line of results, often referred to as search engine results pages (SERPs). The information may be a mix of web pages, images, videos, infographics, articles, research papers and other types of files. Some search engines also mine data available in databases or open directories. Unlike web directories, which are maintained only by human editors, search engines also maintain real-time information by running an algorithm on a web crawler. Internet content that is not capable of being searched by a web search engine is generally described as the deep web.

1. Search EnginesSearch Engines
Presented by
ganesh kavhar

2. 2
What Are They?What Are They?
 Four Components
 A database of references to webpages
 An indexing robot that crawls the WWW
 An interface

Enables users to submit queries

Displays results
 Information retrieval system
 Each is unique, but are mostly the
same

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DatabaseDatabase
 Where user's query is matched
 Contains only essential parts of pages
 Only includes pages that were indexed
 Search engines are always out of date

4. 4
Web CrawlerWeb Crawler
 A robot that follows links
 Records data it finds
 Words in the webpage
 Metadata
 ALT attributes in IMG tags
 Robot Exclusion Protocol

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Search Engine InterfacesSearch Engine Interfaces
 Gathers input from users
 Presents results from the IR system
 Often in ranked order

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Search Engine InterfacesSearch Engine Interfaces
 Input
 User requirements

Search expression, search limits
 Presentation style

Presentation format , search type

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Search Engine InterfacesSearch Engine Interfaces
 Output
 Results
 Descriptions
 Clusters

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Search Term MatchingSearch Term Matching
 Trying to find a match in the database
 Two main methods
 Keyword searching

Matching single terms, computing cosine
 Concept-based searching

Examining clusters of words

Attempt to determine meaning of query and
find records related to that meaning

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Basic IR FeaturesBasic IR Features
 Boolean operators
 AND, OR, NOT, grouping
 Extended operators
 NEAR, ADJACENT, (")
 Stop word deletion
 Stemming
 Searching in fields (e.g. host)

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Ranked OutputRanked Output
 Most SEs produce ranked lists by applying
simple rules:
 Early words are more important
 Title is very important
 Frequency of occurrence matters for some
 Infrequent words matter more
 Modification date
 Google is different:
 PageRankTM
method based on popularity
 Links as money

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GooglebombingGooglebombing
 Google spoofed from the lecture list
 first hit from 1992
 Official GoogleBlog explanation

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What about the Invisible Web?What about the Invisible Web?
 Also known as the Deep Web
 Documents that are on the WWW but
not indexed by Search Engines
 Some are available only by submitting
forms
 Some are not generally accessible (in
subnets)
 Some are not in (X)HTML format

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The Invisible Web Isn't SoThe Invisible Web Isn't So
Invisible Anymore…Invisible Anymore…
 More search engines parse non-
(X)HTML now than before
 Because of awareness of the problem
companies are making more content
available using
 Stable URLs
 Robot-friendly sitemaps
 But much content is still not indexed

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But, there's still plenty ofBut, there's still plenty of
important yet invisible docsimportant yet invisible docs
 How to find them?
 Many of them are in databases
 No one search engine covers everything
 Use database tools from the U.'s library
 Especially for research articles
 Use multiple search engines or a meta-
crawler
 dogpile is the most famous

15. Search EnginesSearch Engines
A Summary of Practical Advice

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How To Succeed With SEsHow To Succeed With SEs
 As a surfer:
 If you don't know what you are looking for

Use multiple SEs, or a meta-crawler

Search within results
 If you don't know what you are looking for

Use multiple SEs, or a meta-crawler

Use Boolean expressions or search within
results

Consider specialized engines

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How To Succeed With SEsHow To Succeed With SEs
 As a creator:
 HTML level

Always use ALT attributes with <IMG>, etc.

Avoid frames
 Make it easier to index

Don't expect SEs to find your pages

Make links between your pages

Use metadata

Informal: <meta name="description" …>

Formal: Dublin core and others
 Increase your pages popularity

Don’t use systematic reciprocal linking: rings, exchanges, lists

Page Rank™ is inversely proportional to outdegree

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How To Succeed With SEsHow To Succeed With SEs
 As a creator (cont.)
 For surfers:
 Use <meta name="description" …>
 Don't expect surfers to start at top of your
hierarchy

Don't rely on a hierarchy

Include a context map near the top of each page

Don't use frames

Think through dynamic content implications

Stickiness… is for another day

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