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Internet search engine

 

 
 
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Published:  January 16, 2010
 
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Slide 1: Mag. iur. Dr. techn. Michael Sonntag Search engines Methods, advertisements, website integration Institute for Information Processing and Microprocessor Technology (FIM) Johannes Kepler University Linz, Austria E-Mail: sonntag@fim.uni-linz.ac.at http://www.fim.uni-linz.ac.at/staff/sonntag.htm © Michael Sonntag 2004
Slide 2: ? ? ? © Michael Sonntag 2004 ? ? Questions? Please ask immediately! ?
Slide 3: Introduction How search engines work Spiders/Bots Indexing Ranking Search engine spamming What to avoid to receive no penalties... Search engines for own websites Frontpage Apache Lucene Commercial software Michael Sonntag Search engines 3
Slide 4: Different "Search engines" Crawlers: Automatically indexing the web Visits all reachable pages in the Internet and indexes them Directories: Humans look for interesting pages Manual classification: Hierarchy of topics needed High quality: Everything is manually verified » This takes care of a general view only (=page is on the topic it states it is about) » Whether the content is legal, correct, useful, etc. is NOT verified! Slow: Lots of human resources required » Cannot keep up with the growth of the Internet! Expensive: Because of manual visits and revisits Very important for special areas! Now almost no importance for general use Mixed versions Michael Sonntag Search engines 4
Slide 5: Spiders Actually creating the indices of crawler-type engines Requires starting points: Entered by owners of webpages Visits the webpage and indexes it, extracts all links, adds the new links to the list of pages to visit » Exponential growth; massively parallel; extreme internet connection required; with special care distribution possible » This might not find all links, e.g. links constructed by JavaScript are usually not found (those mentioned in JavaScript are!) Regularly revisits all pages for changes » Strategies for timeframe exist » Employ hashmarks/date of last change to avoid reindexing Pages created through forms will not be visited! » Spiders can only manage to "read" ordinary pages » Filling in form is impossible (what to fill in where?) Michael Sonntag Frames and image maps can also cause problems engines Search 5
Slide 6: "robots.txt" Allows administrators to forbid indexing/crawling of pages This is a single file for the whole server Must be in the top-level directory! » Exact name: http://<domain name>/robots.txt Alternative: Specify in Meta-Tags of a page Robots.txt Format: "User-agent: " Name of robot to restrict; use "*" for all "Disallow: " Partial URL which is forbidden to visit » Any URL starting with exactly this string will be omitted – "Disallow: /help" forbids "/help.htm" and "/help/index.htm" "Allow: " Partual URL which may be visited » Not in original standard! Visit-time, Request-rate are other new directives Most robots actually follow this standard and respect it! Michael Sonntag Search engines 6
Slide 7: No-robots Meta-Tags Can be added into HTML pages as Meta-Tags: <META NAME="ROBOTS" CONTENT="INDEX,FOLLOW"> – Alternative: CONTENT="ALL" » Index page, also handle all linked pages <META NAME="ROBOTS" CONTENT="NOINDEX,FOLLOW"> » Do not index this page, but handle all linked pages <META NAME="ROBOTS" CONTENT="INDEX,NOFOLLOW"> » Index this page, but do not follow any links <META NAME="ROBOTS" CONTENT="NOINDEX,NOFOLLOW"> – Alternative: CONTENT="NONE" » Do not index this page and do not follow any links Follow: Follow the links in the page. This is not affected by the hierarchy (e.g. pages on level deper on the server)! Non-HTML pages: Must use robots.txt » No "external" metadata defined! Michael Sonntag Search engines 7
Slide 8: Indexing Indexing is extracting the content and storing it Assigning the word to the page under which it will be found later on when users are searching Uses similar techniques as handling actual queries Stopword lists: What words do not contribute to the meaning » Examples: a, an, in, the, we, you, do, and, ... Word stemming: Creating a canonical form » E.g. "words" "word", "swimming" "swim", ... Thesaurus: Words with identical/similar meaning; synonyms » Used probably only for queries! Capitalization: Mostly ignored (content important, not writing) Some search engines also index different file types Michael Sonntag E.g. Google also indexes PDF files Multimedia content very rarely indexed (e.g. videos???) Search engines 8
Slide 9: From text to index HTML PDF Field extraction Content Metadata Indexing Index Text extraction Tokenizer Word filtering Word stemming Text extraction: Retrieving the plain content text Tokenizer: Splitting up in individual words Word filtering: Stop words, lowercase Word stemming: Removing suffixes, different forms, etc. Field extraction: Identifying separate parts E.g. text vs. metadata Michael Sonntag Search engines 9
Slide 10: Page factors Word frequency: A word is the more important, the more often it occurs on a page Also scans for ALT tags of images and words in the URL Modified according to the location: title, headlines, text,... » Higher on the page = better Clustering: How many "nearby" pages contain the same word » "Website themes": Related webpages should be linked Meta-Tags: Might be used as "important", just text or ignored Distance between words: When searching for several words » "gadget creator" will match better than "creator for gadgets" In-Link frequency: How many pages link to this page Mostly those from different domain names used only! Might also depend on keywords on that pages The most important figure currently ( Google!) Michael Sonntag Search engines 10
Slide 11: Page factors Page design: Load time, frames, HTML conformity, ... Some elements cannot be handled (well), e.g. Frames Size of the page (=loadtime) also has influence HTML conformity is not used directly, but if parsing is not possible or produces problems, the page might be ignored Visit frequency: If possible to determine (rare) How often is the site visited through the SE? How long till the user clicks on the next search result? Payment: Search engines also sell placement Nowadays only possible with explicit marking (as paid-for) Update frequency: Regular updates/changes = "live" site Differs much between various search engines! Avoid spamming, this reduces the page value enormously! Michael Sonntag Search engines 11
Slide 12: Searching Form data Query analyzer Result list generation Response Word filtering Word stemming Searching Sorting Caching Query analyzer: Breaking down into individual clauses Clause: Terms connected by AND, OR, NEAR, ... Word filtering: Stop words, lowercase Word stemming: Removing suffixes, different forms, etc. Caching: For next page or refined searches Michael Sonntag Search engines 12
Slide 13: Search engine spamming (1) Artificially trying to improve the position on the result page Important: Through unfair practices! » =deceiving the relevancy algorithm Pages decided to use spamming are heavily penalized or excluded completely (there is no "appeal" procedure!) Test: Would the technique be used even if there were no search engine around at all? Examples for spamming: Repetition of keywords: "spam, spam, spam, spam" » Both after each other or just excessively Separate pages for spiders (e.g. by user agent field) » They might try retrieving the page in several ways Invisible text: white (or light gray) on white Michael Sonntag » Through font color, CSS, invisible layers, ... Search engines 13
Slide 14: Search engine spamming (2) More spamming examples: Misusing tags: Difficulty: What is spam and what is not? » noframes, noscript, longdesc,... tags for spam content » DC metadata the same Very small and very long text: "Nearly" invisible! Identical pages linked to each other or mirror sites » One page accessible through several URLs » To create themes or as link frams (see below) Excessive submissions (submission of URLs to crawl) » Be careful with submission programs! Meta refresh tags/300 error codes/JavaScript » E.g. <body onMouseOver="eval(unescape('.....'))"> » Used to present something other to the spider (initial page) than to the user (page redirected to);if required server side redirects Michael Sonntag Code swapping: One page for index, later change content Search engines 14
Slide 15: Search engine spamming (3) More spamming examples: Cloaking: Returning different pages according to domain name and/or IP of the requester » IP adresses/names of search engine spiders are known Link farms: Network of pages under different domain names » Sole purpose: Creating external links through heavy cross links – Graph theory used to determine them (closed group of heavily interconnected sites with almost no external links) Irrelevant keywords: No connection to text (e.g. "sex") » E.g. in meta tag but not in text; just to attract traffic Meta refresh tags: Automatically moving to another page » Used to present something other to the spider (initial page) than to the user (page redirected to) » If required use server side redirects Michael Sonntag Doorway pages, machine generated page loops, WIKI links,... Search engines 15
Slide 16: Semantic Web The idea is to improve the web through metadata Describing the content in more detail, according to more properties and relating them to each other Machine understandable information on the content » Danger of a new spam method! Allow searching not only for keywords, but also for media types, authors, related sites Nevertheless, some parts are already possible through "conventional" search engines! » The advantage would be in better certainty The result would also be provably correct! » But only as long as both rules and base data are correct! Might be useful, but is still not picking up Requires site owners to add this metadata to their pages Michael Sonntag Search engines 16
Slide 17: Commercial search engine services Pay for inclusion/submission: Pay to get listed Available for both search engines and directories » More important for directories, however! Usually a flat fee, depending on the speed for inclusion May depend on the content; may be recurring or once » E.g. Yahoo: Ordinary site: US$ 299, "Adult content": US$ 600 Usually there is no content/ranking/review/... Guarantee » Solely that it will be processed within a short time (5-7 days)! Pay for placement: Certain placement guaranteed Now commonly paid per click: Each time a user clicks on link » Previously (before dot-com crash): Pay-per-view Separate from "ordinary" links: Else legal problems possible Sometimes rather rare (couldn't find ANY on Yahoo) » Google: Rather common Michael Sonntag Search engines 17
Slide 18: Pay per click (PPC) Advantages: Low risk: Only real services (=visits) are paid for Targeted visitors: Most campaigns match ads to search words Measurable result: Usually tracking available » To determine whether the visitor actually bought something Total budget can be set Problems: Too much/too low success: Prediction difficult Requires exact knowledge of how much a visitor to the site is worth to allow sensible bidding on terms Click fraud: Automatic software or humans do nothing but clicking on paid for links » Affiliate programs making money through this, competitors to exhaust your budget Michael Sonntag Search engines 18
Slide 19: Google AdWords Paid placement; will show up separately on right hand side Cost per Click (CPC); daily upper limit can be set CPC is variable within a user specified range » If range to low it will not show up! » Similar to bidding: The highes bidder will show up – Low bidders will also show up, but only rarely: High CTR improves Ranking: Based on CPC and clickthrough rate (CTR) Ads not clicked on will get lower! Online performance reports Targeting by language and country possible Reduced "ad competition" and enhances click rate Negative keywords possible to avoid unwanted showings Michael Sonntag Search engines 19
Slide 20: Overture SiteMatch / PrecisionMatch Overture: Powers Yahoo, MSN, Alltavista, AllTheWeb, ... SiteMatch: Paid inclusion (fast review and inclusion) "Quality review process": Probably by experts (good assignment of keywords/categories) and favorably » List of exclusion still applies (e.g. online gambling) Pair per URL, i.e. homepage and subpages are separate Pages are re-crawled every 48 hours Positioning in result by relevance: No "moving up" or "top"! Costs: Annual subscription (US$ 49/URL) » Additional pay per click (US$ 0,15/0,3 / click) PrecisionMatch: Paid listing (sponsored results list) Position determined by bidding Pricing not available (demo: US$ 0,59 bidding value) Michael Sonntag » US$ 20 minimum per month??? Search engines 20
Slide 21: Search engine integration Local search engine for a single site Can again be of both kinds » Search engine: Special software required – Automatic update (re-crawling) – Configurable: Visual appearence, options, methods, ... » Directory: Manual creation; no special software needed (CMS) – Regular manual updates required Usually search engine is used » Directory is the "normal" navigation structure Necessity for larger sites Difficulty: Often special requirements needed » Full-text search engine for documents » Special search engine for product search » Special result display for forums, blogs, ... Michael Sonntag Search engines 21
Slide 22: Features for local search engines (1) Language suport: Word stemming, stop words, etc. Also important for user interface (search results) Stop words: Should be customizable Spell checking: For mistyped words File types supported: PDF, Word, multimedia files, .... Configurable spider: Time of day, server load, etc. Spidering through the web or on the file system level? Can password-protected pages also be crawled? Crawling of personalized pages? Search options: Boolean search, exact search, wildcards, ... Quality of search: Difficult to assess, however! Inclusion, exclusion, "near" matches, phrase matching, synonyms, acronyms, sound matching Michael Sonntag Search engines 22
Slide 23: Features for local search engines (2) Admin configurability: Layout customization, user rights, definition of categories, file extensions to include, description of result items, ... User configurability: E.g. Results per page, history of last searches, descriptions shown, sub-searches, etc. Reports and statistics: Top successful queries: What users are most interested in, but cannot find easily Top unsuccessful queries: What would also be of interest » Or where the search engine failed Referer: On which page they started to search for something Top URLs: Which pages are visited most through searching Adheres to "robots.txt" specification? Michael Sonntag Search engines 23
Slide 24: Features for local search engines (3) Indexing restrictions: Excluding parts form crawling/indexing Internal/private pages! Relevancy configuration: Weight of individual elements E.g. if everywhere good metadata is in, this can receive high priority; title tag, links, usage statistics, custom priority, etc. Server based, appliance or local: Where is the engine? Additional features: Automatic site map: Hierarchy/links from where to where Automatic "What's new" list Highlighting: Highlight search words in result list and/or actual result pages "Add-ons": Free offers usually contain advertisements Michael Sonntag Search engines 24
Slide 25: Jakarta Lucene Free search engine; pure Java Open source; freely available Features: Incremental indexing » Indexing only new or changed documents; can remove deleted documents from index Searching: Boolean and phrase queries, date-range » Field searching (e.g. in "title" or in "text") » Fuzzy queries: Small mistypings can be ignored Universally usable: Searching for files in directories, web page searches, offline documentation, etc. » No webserver needed; also possible as stand-alone Completely customizable Michael Sonntag Search engines 25
Slide 26: Jakarta Lucene: Missing features "Plug&Play": Installing, configuring and working site search Not available: Programm needed for indexing, field definition Complicated search options: sound (but see "Phonetix"), synonyms, acronyms Spell checking not available No spider component Examples contain filesystem spider is basic form » Problems with path differences (webserver ↔ index) possible "robots.txt" not supported Reports/statistics must be manually programmed No file types supported: Example contains HTML Word, PDF, etc. easily added, however! Not easily deployed, but good idea for special applications! Michael Sonntag Search engines 26
Slide 27: Search Engine Optimization (SEO) Paid services to optimize a website for search engines Usually also includes submission to many search engines » How man search engines are really of any importance today? – These are very few: They can be "fed" by hand also easily! » Doesn't work to well for directories: Long time without payment; important directories are small and specialized ones, which are probably not covered Often contains rank guarantees » This is to be taken with very much caution: They really cannot guarantee this, therefore illegal methods or spamming is used – E.g. Link farms, to provide this rank once for a short time First page/<50: Are users still convinced that everything important is there? » Many can do without top listing; especially very generic terms! Michael Sonntag Search engines 27
Slide 28: Promoting your website My thoughts Avoid all pitfalls and search engine spamming Use tools to verify suitability of webpages Keywords, keyword density; HTML verification; style guides;... Focus on specific terms and phrases as keywords Avoid "sex", "car", "computers"; use "used porsche cars", ... Provide valuable information to visitors FAQ, hints, comparisons, ...: This will get you external links Submit to the 5 top most crawlers and the 10 most important (for your business!) directories Wait long time to get listed before re-submitting Currently some engines take up to two month Do not depend on visitors: Focus on customers! E.g. avoid ad selling Use other advertisement avenues too, if possible Michael Sonntag Search engines 28
Slide 29: Legal aspects Search engine "optimization" can lead to legal problems Examples are: Very general terms, e.g. "divorceattorney.com" » Channeling users away from competitors » Decisions mixed: Sometimes allowed, sometimes not – Depends also on content: Does it claim to be "the only one"? Unrelated words in meta-tags » E.g. using "legal studies" for a website selling robes for judges – Probably allowed as long as no channeling takes place Trademarks: Using "foreign" trademarks in meta-tags Liability for links to illegal content Search engines and copyright Discussion according to EU (and Austrian) law! Michael Sonntag Search engines 29
Slide 30: Trademarks Using trademarks, service marks, common law marks, etc. of competitors on the own site (or in own meta-tags) » This applies only to commercial websites Depends on whether there is a legally acceptable reason for inclusion on the webpages » Example: Allowed product comparison, other suppliers, selling those products, ... In general this is very dangerous/forbidden » Trademark law: Illegal "use" of a mark » Competition law: "Freeriding" on others fame » Competition law: Customer diversion Search engines: Results may contain the trademark Can even contain links to infringing sites; see below Legal status not completely decided; invisibility when using in a meta-tag is the best argument to no liability Michael Sonntag Search engines 30
Slide 31: Search engine liability Liability for the links itself depend on several elements Directories provide pre-verification » See link liability below! Paid for links are selected; depending on selling method knowledge may or may not exist by default » One of the exceptions from the no-liability clause: – "Selection or modification of content" » Hosting: Full liability as soon as knowledge of illegal content is present; illegality must be clear even for laymen Automatically gathered and presented links are privileged » Only for foreign content (site search engines full liability) » This even applies if knowledge of illegal content is present! – Exception: Knowlingy furthering the illegal activity No obligation to actively search for anything illegal! Michael Sonntag Search engines 31
Slide 32: Link liability General liability of links; also applies to directories Any time a link is sonsciously created Liability by default if the content linked to is "integrated" = made to own content (link just to avoid re-typing it) Depends on the context of the link No liability for foreign information if No knowledge of illegality of content » If something illegal is in a directory, knowledge will exist through pre-approval process! » "Illegality" must be obvious to laymen; suspicions insufficient If knowledge attained, immediately takes step to remove link » This will be quite fast as the Internet is a fast medium! No obligation to actively search for anything illegal! Michael Sonntag Search engines 32
Slide 33: Search engines and copyright Image thumbnail archives Google also indexes images This in itself is no problem For preview, a smaller version of the image is created and stored locally; this is shown alongside the link Reducing an image's size is a modification of the original picture and therefore requires the owners permission » Unless the content is no longer discernible Therefore this practice is forbidden! Similarity: Extracting the description of the webpage and showing it with the link This is however a privileged use ("small citation") » Additionally this is the intended use for the meta tag! Currently ongoing litigation; final decision pending! Michael Sonntag http://www.jurpc.de/rechtspr/20040146.pdf Search engines 33
Slide 34: Literature Robot Exclusion Standard: http://www.conman.org/people/spc/robots2.html http://www.robotstxt.org/ Jared M. Spool: Why On-Site Searching Stinks http://www.uie.com/articles/search_stinks/ Michael Sonntag Search engines 34

   
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