Product Listings: If you sell a catalog of products, search engines like Google and Bing offer a specific ad type called product listing ads or PLA’s. These ads highlight your products, including a product image, and have become far more prominent in search results over the past year or two. These ads can do wonders to attract potential customers who are looking for what you’re selling.
The landing page from ad #2 is shown below. Again, I expected to see left handed golf clubs, and yet again, I was shown a page full of content not directly relevant to my search term. The only reason I would let this slide as a “good” experience is because it presents three major brands (along with a deal) on the landing page, which may convince me to invest a few more clicks to find what I’m looking for.
There’s obviously a huge number of reasons why a website might link to another and not all of them fit into the categories above. A good rule of thumb on whether a link is valuable is to consider the quality of referral traffic (visitors that might click on the link to visit your website). If the site won’t send any visitors, or the audience is completely unrelated and irrelevant, then it might not really be a link that’s worth pursuing.
i.e. the PageRank value for a page u is dependent on the PageRank values for each page v contained in the set Bu (the set containing all pages linking to page u), divided by the number L(v) of links from page v. The algorithm involves a damping factor for the calculation of the pagerank. It is like the income tax which the govt extracts from one despite paying him itself.
Meanwhile, the link spam began. People chasing higher PageRank scores began dropping links wherever they could, including into blog posts and forums. Eventually, it became such an issue that demands were raised that Google itself should do something about it. Google did in 2005, getting behind the nofollow tag, a way to prevent links from passing along PageRank credit.
Mega-sites, like http://news.bbc.co.uk have tens or hundreds of editors writing new content – i.e. new pages - all day long! Each one of those pages has rich, worthwile content of its own and a link back to its parent or the home page! That’s why the Home page Toolbar PR of these sites is 9/10 and the rest of us just get pushed lower and lower by comparison…
As an example, people could previously create many message-board posts with links to their website to artificially inflate their PageRank. With the nofollow value, message-board administrators can modify their code to automatically insert "rel='nofollow'" to all hyperlinks in posts, thus preventing PageRank from being affected by those particular posts. This method of avoidance, however, also has various drawbacks, such as reducing the link value of legitimate comments. (See: Spam in blogs#nofollow)
By relying so much on factors such as keyword density which were exclusively within a webmaster's control, early search engines suffered from abuse and ranking manipulation. To provide better results to their users, search engines had to adapt to ensure their results pages showed the most relevant search results, rather than unrelated pages stuffed with numerous keywords by unscrupulous webmasters. This meant moving away from heavy reliance on term density to a more holistic process for scoring semantic signals. Since the success and popularity of a search engine is determined by its ability to produce the most relevant results to any given search, poor quality or irrelevant search results could lead users to find other search sources. Search engines responded by developing more complex ranking algorithms, taking into account additional factors that were more difficult for webmasters to manipulate. In 2005, an annual conference, AIRWeb, Adversarial Information Retrieval on the Web was created to bring together practitioners and researchers concerned with search engine optimization and related topics.