© Tefko Saracevic 1 part 1: search engines part 2: digital libraries.
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Transcript of © Tefko Saracevic 1 part 1: search engines part 2: digital libraries.
© Tefko Saracevic 2
dictionary definitions
searchCOMPUTING (transitive verb) to examine a computer
file, disk, database, or network for particular information
enginesomething that supplies the driving force or energy to
a movement, system, or trend
search enginea computer program that searches for particular
keywords and returns a list of documents in which they were found, especially a commercial service that scans documents on the Internet
© Tefko Saracevic 3
about definition of search engines
• oh well … search engines do not search only for
keywords, some search for other stuff as well
• and they are really not “engines” in the classical sensebut then mouse is not a “mouse”
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Your Browser
How Search Engines Work(Sherman 2003)
The Web
URL1
URL2
URL3 URL4
Crawler
Indexer
SearchEngine
Database Eggs?Eggs.
Eggs - 90%Eggo - 81%Ego- 40%
Huh? - 10%
All AboutEggsby
S. I. Am
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how do search engines work? elaboration
• crawlers, spiders: go out to find content in various ways go through the web
looking for new & changed sitesperiodic, not for each query
no search engine works in real time
some search engines do it for themselves, others not
buy content from companies such as Inktomi
for a number of reasons crawlers do not cover all of the web – just a fraction
what is not covered is “invisible web”
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elaboration …• organizing content: labeling, arranging
indexing for searching – automatic keywords and other fields arranging by URL popularity - PageRank as Google
classifying as directory mostly human handpicked & classified
• as a result of different organization we have basically two kinds of search engines:
search – input is a query that is then searched & displayed
directory – classified content – a class is displayed– and fused: directories have now also search
capabilities & vice versa
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elaboration (cont.)
• databases, caches: storing content humongous files usually distributed over many
computers
• query processor: searching, retrieval, display takes your query as input
engines have differing rules how handled displays ranked output
some engines also cluster output and provide visualization
• at the other end is your browser
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elaboration…similarities, differences
• all search engines have these basic parts in common
• BUT the actual processes – methods how they do it – are based on various algorithms & they differ most are proprietary with details kept
mostly secret but based on well known principles from information retrieval or classification
to some extent Google is an exception – they published their method
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case of
• developed by Sergey Brin and Lawrence Page while students at Stanford in the beginning run on Stanford computers
• basic approach has been described in their famous paper “The Anatomy of a Large-Scale Hypertextual Web Search Engine” well written, simple language, has their pictures in acknowledgement they cite the support by NSF’s
Digital Library Initiative i.e. initially, Google came out of government sponsored research
describe their method PageRank - based on ranking hyperlinks as in citation indexing
“We chose our system name, Google, because it is a common spelling of googol, or ten on hundredth power”
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coverage differences
• no engine covers more than a fraction of WWW estimates: none more than 16% hard (even impossible) to discern & compare coverage, but
they differ substantially in what they cover
• in addition: many national search engines
own coverage, orientation, governance many specialized or domain search engines
own coverage geared to subject of interest many comprehensive sources independent of search
engines some have compilations of evaluated web sources
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searching differences
• substantial differences among search engines on searching, retrieval displayneed to know how they work & differ in
respect to defaults in searching a query searching of phrases, case sensitivity, categories searching of different fields, formats, types of
resources advance search capabilities and features possibilities for refinement, using relevance
feedback display options personalization options
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business model differences
several business models• public good - have independent budget
e.g. PubMed, Librarians’ Index to Internet
• earn revenue from provision of information all commercial search engines
• using search engines to promote their other activities e.g. telephone directories
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sponsorship differences
• need to understand treatment of sponsorship – they influence what they search & how they display resultssome list separately results from sponsored
sites so you are reasonably clear what is there because it is sponsored & not
some have display-per-pay - showing first sites that paid most & do not even tell you that
some have pay per update of sites
• imperative to find sources that explain these models for different engines to know what is covered & what are you are getting
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limitations
• every search engine has limitation as tocoverage
meta engines just follow coverage limitations & have more of their own
search capabilitiesfinding quality information
• some have compromised search with economics becoming little more than advertisers
• but search engines are also many times victims of spamindexingaffecting what is included and how ranked
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spamming a search engine
• use of techniques that push rankings higher than they belong is also called spamdexing methods typically include textual as well as
link-based techniques like e-mail spam, search engine spam is a
form of adversarial information retrieval the conflicting goals of accurate results of search
providers & high positioning by content page rank
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meta search engines
• meta engines search multiple engines getting combined results from a
variety of engines
• do not have their own databasesbut have their own business models
affecting results
• a number of techniques usedinteresting ones: clustering, statistical
analyses
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how to find a search engine?
• variety of resources that list or categorize engines
• SearchEngines.comsearch for engines by topic, geography, reference
Search Engine Guideengines categorized by topic; other engine information
Search Engine Colossus international directory of search engines by country, topic from
198 countries and 61 territories; engines in choice of languages
Phil Bradley’s country based search enginesover 2000 serach engines from countries all over the globe
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sample of meta engines- with organized results
Dogpile results from a number of leading search engines;
gives source, so overlap can be compared; (has also a (bad) joke of the day)
Surfwax gives statistics and text sources & linking to
sources; for some terms gives related terms to focus
Teomaresults with suggestions for narrowing; links
resources derived; originated at Rutgers
Turbo10provides results in clusters; engines searched can
be edited
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meta search engines (cont.)
• Large directory Complete Planet
directory of over 70,000 databases & specialty engines
• Results with graphical displays Vivisimo
clusters results; innovative
Webbrain results in tree structure – fun to use
Kartooresults in display by topics of query
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domain engines & catalogs
• cover specific subjects & topics• important tool for subject searches
particularly for subject specialistvalued by professional searchers
• selection mostly hand-picked rather than by crawlers, following inclusion criteriaoften not readily discernablebut content more trustworthy
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domain engines … sample
Open Directory Project large edited catalog of the web – global, run by
volunteers
BUBL LINK selected Internet resources covering all academic
subject areas; organized by Dewey Decimal System – from UK
Profusion search in categories for resources & search engines
Resource Discovery Network – UK“UK's free national gateway to Internet resources for
the learning, teaching and research community”
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domain engines … sample
Think Quest – Oracle Education Foundation • education resources, programs; web sites created by students
All Music Guide • resource about musicians, albums, and songs
Internet Movie Database • treasure trove of American and British movies
Genealogy links and surname search engineswell.. that is getting really specialized (and popular)
Daypopsearches the “living web” “The living web is composed of sites
that update on a daily basis: newspapers, online magazines, and weblogs”
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science, scholarship engines …sample free
access Psychcrawler - Amer Psychological
Association web index for psychology
Entrez PubMed – Nat Library of Medicinebiomedical literature from MEDLINE & health journals
CiteSeer - NEC Research Center scientific literature, citations index; strong in computer
science
Scholar Googlesearches for scholarly articles & resources
Infominescholarly internet research collections
Scirusscientific information in journals & on the web
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science, scholarship engines …sample
commercial access • an addition to freely accessible engines
many provide search free but access to full text paid by subscription or per itemRUL provides access to these & many more:
ScienceDirectElsevier: “world's largest electronic collection of science,
technology and medicine full text and bibliographic
information” ACM PortalAsoc. for Computing Machinery: access to ACM Digital Library &
Guide to Computing
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where to find out?
• information about search engines in sources that have updates, news, tips for searching and more – a MUST for searchers : Search Engine Watch
ratings, news, statistics, charts, explanations, tutorials Search Engine Showdown
“The users’ guide to web searching” - run by a librarian, news links, ratings
Virtual Chase a site about “Teaching Legal Professionals How To
Do Research;,” this section has very good tips and links for consideration of quality on the web
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where? ….
SiteLinesa blog, written by Rita Vine, a professional
librarian, & web search trainer; many evaluations in archive
ResourceShelf“Resources and News for Information
Professionals,” edited by Gary Price, a librarian & author of Invisible Web – has extensive archive
WebsearchAboutnot evaluative, but provides news, capabilities,
sources, articles about web searching
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definition
• digital libraries are viewed from several perspectivestechnical: “Digital library is a managed collection
of information, with associated services, where information is stored in digital format and accessible over a network.” (Arms, 2000)
institutional: “Digital libraries are organizations that provide the resources, including the specialized staff, to select, structure, offer intellectual access to, interpret, distribute, preserve the integrity of, and ensure the persistence over time of collections of digital works so that they are readily and economically available for use by a defined community or set of communities.” (Waters, 1998)
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a bit of context
• short but volatile history research & development took of by start/mid
1990’s in the next decade phenomenal growth
worldwide large investment in research & building
• number of communities involvedcomputer science, primarily in researchmany subjects: digital libraries in their domain library & information science: operations, studies
of users, use, usability
• number of types emerged
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libraries & digital resources
• libraries (particularly research, academic & special) directed massive funding toward such resourceselectronic journalsdatabasescatalogsdigitization of parts of collection
• thus becoming in effect digital libraries – or more accurately hybrid libraries with graphic and digital versions or types of
resources
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emphasis here
• on large academic or research digital libraries that also are related to searching provide search capabilities or access to
search enginesprovide electronic journals that provide full
text of articles after a search
• such libraries have become also search portals of sort, essential for their users in education, research & related activities
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sample
New York Public Library Digital“NYPL Digital is your gateway to The New York Public Library’s
rare and unique collections in digitized form.” Includes access to searchable databases
U California Berkeley Digital Library SUNsite“builds digital collections and services while providing
information and support to digital library developers worldwide.
The British Library“The world’s knowledge.” Includes “Services fro library and
information Professionals.”
Los Angeles Public Library Kids’ Pathresources for children; search through directory
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sample …
New Zealand Digital Librarysearching of a number of digital collections, including
humanity development library
Research Library Group“RLG is a not-for-profit organization of over 150 research
libraries, archives, museums, and other cultural memory institutions.” Includes links to a number of searchable collections
Public Library of Science“PLoS is a nonprofit organization of scientists and physicians
committed to making the world's scientific and medical literature a public resource.” Publishes open access journals
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Rutgers libraries – digital components
• strategic planning in developing digital access
• rich & complex content of digital resourcesseveral hundred indexes & databases for
searchingsome 20,000 electronic journals thousand & more digital reference sourcessubject research guidesSearchpath & other tutorialselectronic reserve
• affected teaching, learning, research by the whole community
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some critical issues for searching
• no way yet to do federated searching in digital libraries to search several indexes at the same timeeach source has to be searched separately
most have very different search features, capabilities
• finding items in indexes does not mean that always able to get full text
• thus, searching time-consuming, chaotic
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where to find out?
• information about digital libraries LibWeb U California, Berkeley“lists currently over 7200 pages from libraries in over 125
countries”
Digital Library Federation“a consortium of libraries and related agencies that are
pioneering the use of electronic-information technologies to extend their collections and services”
D-Lib Magazine“a solely electronic publication with a primary focus on
digital library research and development, including but not limited to new technologies, applications, and contextual social and economic issues”
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where? …
Ariadne (UK)“to report on information service developments and
information networking issues worldwide, keeping the busy practitioner abreast of current digital library initiatives”
Information Technology and LibrariesALA publication; “related to all aspects of libraries and
information technology, including digital libraries” Journal of Digital Information
“Publishing papers on the management, presentation and uses of information in digital environments”
Biblio Tech Review “Information Technology for Libraries” – monthly news
and review magazine
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in conclusion
• search engines are great but you have to KNOW what is under the hoodas to coverage, business model, search
features, outputs … they are NOT for every kind of information
need
• digital libraries are great for searching but you have to KNOW requirements for searching different resources that are included there is no federated searching as yet, or for
the time to come