A Survey of Google's
PageRank
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.
The PageRank Concept
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.
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
were taken from an article which can be found
at http://dance.efactory.de/
(c)2002 eFactory Internet-Agentur KG Online-Marketing
- written by Markus Sobek
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