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A Survey of Google's PageRank |
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Within the past few years, Google has
become the far most utilized search engine worldwide. A
decisive factor therefore was, besides high performance and
ease of use, the superior quality of search results compared
to other search engines. This quality of search results is
substantially based on PageRank, a sophisticated method to
rank web documents.
The aim of these pages is to
provide a broad survey of all aspects of PageRank. The
contents of these pages primarily rest upon papers by Google
founders Lawrence Page and Sergey Brin from their time as
graduate students at Stanford University.
It is often
argued that, especially considering the dynamic of the
internet, too much time has passed since the scientific work
on PageRank, as that it still could be the basis for the
ranking methods of the Google search engine. There is no doubt
that within the past years most likely many changes,
adjustments and modifications regarding the ranking methods of
Google have taken place, but PageRank was absolutely crucial
for Google's success, so that at least the fundamental concept
behind PageRank should still be constitutive. |
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The PageRank Concept
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Since the early stages of the world wide web, search
engines have developed different methods to rank web pages.
Until today, the occurence of a search phrase within a
document is one major factor within ranking techniques of
virtually any search engine. The occurence of a search phrase
can thereby be weighted by the length of a document (ranking
by keyword density) or by its accentuation within a document
by HTML tags.
For the purpose of better search results
and especially to make search engines resistant against
automatically generated web pages based upon the analysis of
content specific ranking criteria (doorway pages), the concept
of link popularity was developed. Following this concept, the
number of inbound links for a document measures its general
importance. Hence, a web page is generally more important, if
many other web pages link to it. The concept of link
popularity often avoids good rankings for pages which are only
created to deceive search engines and which don't have any
significance within the web, but numerous webmasters elude it
by creating masses of inbound links for doorway pages from
just as insignificant other web pages.
Contrary to the
concept of link popularity, PageRank is not simply based upon
the total number of inbound links. The basic approach of
PageRank is that a document is in fact considered the more
important the more other documents link to it, but those
inbound links do not count equally. First of all, a document
ranks high in terms of PageRank, if other high ranking
documents link to it.
So, within the PageRank concept,
the rank of a document is given by the rank of those documents
which link to it. Their rank again is given by the rank of
documents which link to them. Hence, the PageRank of a
document is always determined recursively by the PageRank of
other documents. Since - even if marginal and via many links -
the rank of any document influences the rank of any other,
PageRank is, in the end, based on the linking structure of the
whole web. Although this approach seems to be very broad and
complex, Page and Brin were able to put it into practice by a
relatively trivial algorithm. |
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PageRank and Google are trademarks of Google Inc.,
Mountain View CA, USA.
PageRank is protected by US Patent
6,285,999.
The contents of this document may be
reproduced on the web provided that a copyright notice is
included and that there is a straight HTML hyperlink to the
corresponding page at pr.efactory.de in direct
context. |
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