Article Index
Introduction
The PageRank Algorithm
The Implementation of PageRank
The Effect of Inbound Links
The Effect of Outbound Links
The Effect of the Number of Pages
The Distribution of PageRank
The Yahoo Bonus
Additional Factors Influencing PageRank
Introduction
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.
Technical level: Expert || Date:
20th November 2002 || Author: Markus
Sobek
MIS Editor:
Thanks to pr.efactory.de and Markus Sobek for allowing
us to reproduce this article. PageRank and Google
are trademarks of Google Inc., Mountain View CA, USA.
PageRank is protected by US Patent 6,285,999. Copyright
for this article belongs to pr.efactory.de.
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.
