Saturday, 4 February 2012

Topic-Sensitive PageRank

Topic-sensitive PageRank computes link value based only on incoming links from
pages that are returned from a given search result set that matches the search query
(whether the result set is 100 or 10,000 pages is not known).
This means that a flower site only gets links counted from other sites that are related
to flowers and gardening - not from sites that are about mortgage loans for example.
By using Topic-sensitive PageRank, Google hopes to filter out irrelevant links that
have skewed the value of PageRank in the past.

A variation of PageRank whereby links from sites that share the same Class C
blocks are worth less than links from a variety of different IP addresses, which are
generally different servers owned by different businesses.

As you may recall, a Class C block is that number shown in the third position of an IP
address. For example, for, xxx represents the Class C block.

This attempts to deal with the problem of different sites owned by the same company
that cross-link to each other. Put another way, Google wants to see incoming links
that are from different business entities, not different sites owned by the same

TrustRank and the Sandbox
A variation of PageRank whereby links from site that are “trusted” by Google carry
more weight than other links. This also related to the Google Sandbox. As you
recall, the Google Sandbox is a series of filters applied to new sites that cause them
not to rank well or rank at all for anything but very niche, unique keyword phrases,
such as their company name.

TrustRank says that new websites either have to reach a certain age (say 6 - 18
months) OR obtain relevant, quality links from authoritative "highly-trusted" sites to
escape the Sandbox. However, links from highly-trusted sites can be very difficult for
new sites to get. For this reason, most new sites must be of sufficient age AND the
links that point to new sites need also to be of sufficient age and at least “moderately
trusted" before a new site can rank well.
The TrustRank threshold that new sites need to overcome to escape the Sandbox
varies by keyword and industry. Gambling and pill sites have a much harder time
breaking free from the Sandbox filters than say baby blanket sites.

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