PageRank from Google

There are two major factors on which the pages available in base poiskovika, will be sorted at delivery. It is relevance (that is as far as the considered{examined} page is connected to a subject of search - the factors described in the previous section) both number and quality of external links. Last factor also has received names reference citiruemost`, reference popularity or an index of citing.

Index citiruemosti

It is easy to see, that simple calculation of number of external links does not give us the sufficient information for a rating of a site. It is obvious, that the link from a site www.microsoft.com should mean much more, than the link from a home page www.hostingcompany.com / ~ myhomepage.html, therefore to compare popularity of sites only on number of external links it is impossible - necessary to take into account as well importance of links.

For a rating of number and quality of external links to a site search engines enter concept of an index of citing.

The index of citing or IC is a general{common} designation of the numerical parameters estimating popularity of this or that resource, that is some absolute value of importance of page. Each search engine uses the algorithms for calculation of own index of citing, as a rule, these values are not published anywhere.

Google PageRank

The first who has patented system of the account of external links became company Google. The algorithm has received name PageRank.

The main task consists in finding the criterion expressing importance of page. In a case with PageRank such criterion theoretical attendance of page has been chosen.

Now PageRank it is not used directly in algorithm Google. It and is understandable - in fact PageRank characterizes only quantity{amount} and quality of external links to a site, but at all does not take into account the reference text and information contents of referring pages - namely the maximal value is necessary to these factors at ranging.

It is supposed, that for ranging Google uses so-called thematic PageRank (that is taking into account only links from thematically connected pages), however details of this algorithm are known only to developers Google.

To learn{find out} value PageRank for any web - page it is possible with help Google ToolBar which shows value PageRank in a range from 0 up to 10. It is necessary to take into account, that Google ToolBar shows not exact value PageRank, and only range PageRank in which the site gets, and number{room} of a range (from 0 up to 10) it is defined{determined} on a logarithmic scale:

Real value PR Value ToolBar

1-101

10-1002

100-10003

1000-10.0004

.....

All figures are conditional, however evidently show, that ranges PageRank shown in Google ToolBar, are not equivalent to each other. For example, to lift PageRank c 1 up to 2 it is easy, and with 6 up to 7 it is much more complex{difficult}.

In practice PageRank it is used basically in two purposes:

1. A fast rating of a level raskruchennosti a site. PageRank does not give the exact information on referring pages, but allows "to estimate" a level of development of a site quickly and simply. For English-speaking sites it is possible to adhere to the following gradation: PR 4-5 - the most typical PR for the majority of sites of average raskruchennosti. PR 6 - very well untwisted site. PR 7 - the size practically unattainable for the usual web designer, but sometimes meets. PR 8, 9, 10 - meet only at sites of the large companies (Microsoft, Google, etc.). Knowledge PageRank can be used at an exchange of links to estimate quality of the page offered{suggested} to an exchange and in other similar situations.

2. A rating of a level of a competition on search search. Though PageRank also it is not used directly in algorithms of ranging, nevertheless allows to estimate competition of the set search indirectly. For example, if in delivery of the search engine sites with PageRank 6-7 the site with PageRank 4 has very few chances to rise in top cost{stand}.

One more important remark - values PageRank shown in Google ToolBar are recalculated seldom enough (time in some months), therefore ToolBar shows to a certain extent the out-of-date information. That is search engine Google takes into account changes in external links much faster, than these changes are displayed in Google ToolBar.