Sometimes we rank well on one engine for a particular keyphrase and assume that all search engines will like our pages, and hence we will rank well for that keyphrase on a number of engines. Unfortunately this is rarely the case. All the major search engines differ somewhat, so what’s get you ranked high on one engine may actually help to lower your ranking on another engine.
It is for this reason that some people like to optimize pages for each particular search engine. Usually these pages would only be slightly different but this slight difference could make all the difference when it comes to ranking high.
However because search engine spiders crawl through sites indexing every page it can find, it might come across your search engine specific optimizes pages and because they are very similar, the spider may think you are spamming it and will do one of two things, ban your site altogether or severely punish you in the form of lower rankings.
The solution is this case is to stop specific Search Engine spiders from indexing some of your web pages. This is done using a robots.txt file which resides on your webspace.

A Robots.txt file is a vital part of any webmasters battle against getting banned or punished by the search engines if he or she designs different pages for different search engine’s.
The robots.txt file is just a simple text file as the file extension suggests. It’s created using a simple text editor like notepad or WordPad, complicated word processors such as Microsoft Word will only corrupt the file.
You can insert certain code in this text file to make it work. This is how it can be done.
User-Agent: (Spider Name) Disallow: (File Name)
The User-Agent is the name of the search engines spider and Disallow is the name of the file that you don’t want that spider to index.
You have to start a new batch of code for each engine, but if you want to list multiply disallow files you can one under another. For example –
User-Agent: Slurp (Inktomi’s spider)
Disallow: xyz-gg.html Disallow: xyz-al.html
Disallow: xxyyzz-gg.html Disallow: xxyyzz-al.html
The above code disallows Inktomi to spider two pages optimized for Google (gg) and two pages optimized for AltaVista (al). If Inktomi were allowed to spider these pages as well as the pages specifically made for Inktomi, you may run the risk of being banned or penalized. Hence, it’s always a good idea to use a robots.txt file.
The robots.txt file resides on your webspace, but where on your webspace? The root directory! If you upload your file to sub-directories it will not work. If you wanted to disallow all engines from indexing a file, you simply use the * character where the engines name would usually be. However beware that the * character won’t work on the Disallow line.
Here are the names of a few of the big engines:
Excite – ArchitextSpider AltaVista – Scooter Lycos – Lycos_Spider_(T-Rex) Google – Googlebot Alltheweb – FAST-WebCrawle

Be sure to check over the file before uploading it, as you may have made a simple mistake, which could mean your pages are indexed by engines you don’t want to index them, or even worse none of your pages might be indexed.
Another advantage of the Robots.txt file is that by examining it, you can get information on what spiders, or agents have accessed your web pages. This will give you a list of all the host names as well as agent names of the spiders. Moreover, information of very small search engines also gets recorded in the text file. Thus, you know what Search Engines are likely to list your website.

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Most Search Engines scan and index all of the text in a web page. However, some Search Engines ignore certain text known as Stop Words, which is explained below. Apart from this, almost all Search Engines ignore spam.

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Stop words are common words that are ignored by search engines at the time of searching a key phrase. This is done in order to save space on their server, and also to accelerate the search process.

When a search is conducted in a search engine, it will exclude the stop words from the search query, and will use the query by replacing all the stop words with a marker. A marker is a symbol that is substituted with the stop words. The intention is to save space. This way, the search engines are able to save more web pages in that extra space, as well as retain the relevancy of the search query.
Besides, omitting a few words also speeds up the search process. For instance, if a query consists of three words. The Search Engine would generally make three runs for each of the words and display the listings. However, if one of the words is such that omitting it does not make a difference to search results, it can be excluded from the query and consequently the search process becomes faster.
Some commonly excluded “stop words” are: after also an and as at be
because before between

but
before
for
however
from
if
in
into
of
or
other
out
since
such
than
that
the
these
there
this
those
to
under
upon
when
where
whether
which
with
within
without

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Search engines are unable to view graphics or distinguish text that might be contained within them. For this reason, most engines will read the content of the image ALT tags to determine the purpose of a graphic. By taking the time to craft relevant, yet keyword rich ALT tags for the images on your web site, you increase the keyword density of your site.
Although many search engines read and index the text contained within ALT tags, it’s important NOT to go overboard in using these tags as part of your SEO campaign. Most engines will not give this text any more weight than the text within the body of your site.

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Invisible text is content on a web site that is coded in a manner that makes it invisible to human visitors, but readable by search engine spiders. This is done in order to artificially inflate the keyword density of a web site without affecting the visual appearance of it. Hidden text is a recognized spam tactic and nearly all of the major search engines recognize and penalize sites that use this tactic.

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This is the technique of placing text on a page in a small font size. Pages that are predominantly heavy in tiny text may be dismissed as spam. Or, the tiny text may not be indexed. As a general guideline, try to avoid pages where the font size is predominantly smaller than normal. Make sure that you’re not spamming the engine by using keyword after keyword in a very small font size. Your tiny text may be a copyright notice at the very bottom of the page, or even your contact information. If so, that’s fine.

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Almost all Search Engines serve different countries. Search Engines do list content from other countries but most of the content that is listed is either US or UK dominated content.
With this in mind, most popular Search Engines have started deploying regional editions that serve only a specific country.

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Regional Interface is nothing but a translated version of the main Search Engine. Many Search Engines have interfaces in different languages such as French, German, Spanish, Japanese etc. However, the only difference between these regional interfaces and the main version of the Search Engine is that the language used on the interface is not English. In other words, if you search using a keyword on both the interfaces, the listings are exactly the same.
Regional Interfaces are aimed at an audience that does not understand English.

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Human Categorization, as the name suggests, is categorization of websites by human beings. Search Engine employees categorize different websites into regional listings. Websites that are more relevant to a specific country are listed in that edition of the Search Engine. Hence, for a French edition a search would mainly list documents from France. This eliminates the problem mentioned above. The only caveat being that the whole process is manual.
Directories such as Yahoo, LookSmart, and Open Directory make use of this process.

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Domain Filtering automatically segregates websites from different countries into their respective regional editions. This segregation is done on the basis of domain names. For instance a website from Australia would generally have a domain .au. The Domain filtering mechanism looks at the domains of all websites and creates a country specific edition listing.
Some Search Engines also have region specific editions which contain listings from the whole of that region. As an example: A French edition of Google may also return German or Spanish websites in some cases.
Domain Filtering has a drawback though. This mechanism can only filter out websites based on the domain name, and hence .com is always considered to be a United States website. This is obviously not true. Many websites from other countries also have .com domains.

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