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.
|
