Link Exchange

PageRank Damping factor

2009-07-05T09:40:00.000-07:00

The PageRank theory holds that even an imaginary surfer who is randomly clicking on links will eventually stop clicking. The probability, at any step, that the person will continue is a damping factor d. Various studies have tested different damping factors, but it is generally assumed that the damping factor will be set around 0.85.

The damping factor is subtracted from 1 (and in some variations of the algorithm, the result is divided by the number of documents in the collection) and this term is then added to the product of the damping factor and the sum of the incoming PageRank scores. That is,

or (N = the number of documents in collection)

So any page's PageRank is derived in large part from the PageRanks of other pages. The damping factor adjusts the derived value downward. The second formula above supports the original statement in Page and Brin's paper that "the sum of all PageRanks is one". Unfortunately, however, Page and Brin gave the first formula, which has led to some confusion.

Google recalculates PageRank scores each time it crawls the Web and rebuilds its index. As Google increases the number of documents in its collection, the initial approximation of PageRank decreases for all documents.

The formula uses a model of a random surfer who gets bored after several clicks and switches to a random page. The PageRank value of a page reflects the chance that the random surfer will land on that page by clicking on a link. It can be understood as a Markov chain in which the states are pages, and the transitions are all equally probable and are the links between pages.

If a page has no links to other pages, it becomes a sink and therefore terminates the random surfing process. However, the solution is quite simple. If the random surfer arrives at a sink page, it picks another URL at random and continues surfing again.

When calculating PageRank, pages with no outbound links are assumed to link out to all other pages in the collection. Their PageRank scores are therefore divided evenly among all other pages. In other words, to be fair with pages that are not sinks, these random transitions are added to all nodes in the Web, with a residual probability of usually d = 0.85, estimated from the frequency that an average surfer uses his or her browser's bookmark feature.

So, the equation is as follows:

where p1,p2,...,pN are the pages under consideration, M(pi) is the set of pages that link to pi, L(pj) is the number of outbound links on page pj, and N is the total number of pages.

The PageRank values are the entries of the dominant eigenvector of the modified adjacency matrix. This makes PageRank a particularly elegant metric: the eigenvector is

where R is the solution of the equation

where the adjacency function is 0 if page pi does not link to pj, and normalised such that, for each i

i.e. the elements of each column sum up to 1. This is a variant of the eigenvector centrality measure used commonly in network analysis.

Because of the large eigengap of the modified adjacency matrix above, the values of the PageRank eigenvector are fast to approximate (only a few iterations are needed).

As a result of Markov theory, it can be shown that the PageRank of a page is the probability of being at that page after lots of clicks. This happens to equal t − 1 where t is the expectation of the number of clicks (or random jumps) required to get from the page back to itself.

The main disadvantage is that it favors older pages, because a new page, even a very good one, will not have many links unless it is part of an existing site (a site being a densely connected set of pages, such as Wikipedia). The Google Directory (itself a derivative of the Open Directory Project) allows users to see results sorted by PageRank within categories. The Google Directory is the only service offered by Google where PageRank directly determines display order. In Google's other search services (such as its primary Web search) PageRank is used to weigh the relevance scores of pages shown in search results.

Several strategies have been proposed to accelerate the computation of PageRank.

Various strategies to manipulate PageRank have been employed in concerted efforts to improve search results rankings and monetize advertising links. These strategies have severely impacted the reliability of the PageRank concept, which seeks to determine which documents are actually highly valued by the Web community.

Google is known to actively penalize link farms and other schemes designed to artificially inflate PageRank. In December 2007 Google started actively penalizing sites selling paid text links. How Google identifies link farms and other PageRank manipulation tools are among Google's trade secrets.

PageRank

2009-07-05T09:29:00.004-07:00

PageRank is a link analysis algorithm, named after Larry Page, used by the Google Internet search engine that assigns a numerical weighting to each element of a hyperlinked set of documents, such as the World Wide Web, with the purpose of "measuring" its relative importance within the set. The algorithm may be applied to any collection of entities with reciprocal quotations and references. The numerical weight that it assigns to any given element E is also called the PageRank of E and denoted by PR(E).

The name "PageRank" is a trademark of Google, and the PageRank process has been patented (U.S. Patent 6,285,999). However, the patent is assigned to Stanford University and not to Google. Google has exclusive license rights on the patent from Stanford University. The university received 1.8 million shares of Google in exchange for use of the patent; the shares were sold in 2005 for $336 million.

Description
Google describes PageRank:
“ PageRank relies on the uniquely democratic nature of the web by using its vast link structure as an indicator of an individual page's value. In essence, Google interprets a link from page A to page B as a vote, by page A, for page B. But, Google looks at more than the sheer volume of votes, or links a page receives; it also analyzes the page that casts the vote. Votes cast by pages that are themselves "important" weigh more heavily and help to make other pages "important". ”

In other words, a PageRank results from a "ballot" among all the other pages on the World Wide Web about how important a page is. A hyperlink to a page counts as a vote of support. The PageRank of a page is defined recursively and depends on the number and PageRank metric of all pages that link to it ("incoming links"). A page that is linked to by many pages with high PageRank receives a high rank itself. If there are no links to a web page there is no support for that page.

Google assigns a numeric weighting from 0-10 for each webpage on the Internet; this PageRank denotes a site’s importance in the eyes of Google. The PageRank is derived from a theoretical probability value on a logarithmic scale like the Richter Scale. The PageRank of a particular page is roughly based upon the quantity of inbound links as well as the PageRank of the pages providing the links. It is known that other factors, e.g. relevance of search words on the page and actual visits to the page reported by the Google toolbar also influence the PageRank.[citation needed] In order to prevent manipulation, spoofing and Spamdexing, Google provides no specific details about how other factors influence PageRank.[citation needed]

Numerous academic papers concerning PageRank have been published since Page and Brin's original paper. In practice, the PageRank concept has proven to be vulnerable to manipulation, and extensive research has been devoted to identifying falsely inflated PageRank and ways to ignore links from documents with falsely inflated PageRank.

Other link-based ranking algorithms for Web pages include the HITS algorithm invented by Jon Kleinberg (used by Teoma and now Ask.com), the IBM CLEVER project, and the TrustRank algorithm.

Algorithm

PageRank is a probability distribution used to represent the likelihood that a person randomly clicking on links will arrive at any particular page. PageRank can be calculated for collections of documents of any size. It is assumed in several research papers that the distribution is evenly divided between all documents in the collection at the beginning of the computational process. The PageRank computations require several passes, called "iterations", through the collection to adjust approximate PageRank values to more closely reflect the theoretical true value.

A probability is expressed as a numeric value between 0 and 1. A 0.5 probability is commonly expressed as a "50% chance" of something happening. Hence, a PageRank of 0.5 means there is a 50% chance that a person clicking on a random link will be directed to the document with the 0.5 PageRank.

Simplified algorithm
Assume a small universe of four web pages: A, B, C and D. The initial approximation of PageRank would be evenly divided between these four documents. Hence, each document would begin with an estimated PageRank of 0.25.

In the original form of PageRank initial values were simply 1. This meant that the sum of all pages was the total number of pages on the web. Later versions of PageRank (see the below formulas) would assume a probability distribution between 0 and 1. Here a simple probability distribution will be used- hence the initial value of 0.25.

If pages B, C, and D each only link to A, they would each confer 0.25 PageRank to A. All PageRank PR( ) in this simplistic system would thus gather to A because all links would be pointing to A.

This is 0.75

Again, suppose page B also has a link to page C, and page D has links to all three pages. The value of the link-votes is divided among all the outbound links on a page. Thus, page B gives a vote worth 0.125 to page A and a vote worth 0.125 to page C. Only one third of D's PageRank is counted for A's PageRank (approximately 0.083).

In other words, the PageRank conferred by an outbound link L( ) is equal to the document's own PageRank score divided by the normalized number of outbound links (it is assumed that links to specific URLs only count once per document).

In the general case, the PageRank value for any page u can be expressed as:

i.e. the PageRank value for a page u is dependent on the PageRank values for each page v out of the set Bu (this set contains all pages linking to page u), divided by the number L(v) of links from page v.

Obtaining backlinks from search engines

2009-07-05T09:29:00.003-07:00

Most commercial search engines provide a mechanism to determine the number of backlinks they have recorded to a particular web page. For example, Google can be searched using link:wikipedia.org to find the number of pages on the Web pointing to http://wikipedia.org/. Google only shows a small fraction of the number of links pointing to a site. It credits many more backlinks than it shows for each website.

Yahoo!’s Site Explorer is a favorite method of obtaining the number of backlinks on a site, because this tool shows a larger number of the actual backlinks than any other tool.

Search engine rankings

2009-07-05T09:29:00.001-07:00

Search engines often use the number of backlinks that a website has as one of the most important factors for determining that website's search engine ranking. Websites often employ various techniques (called search engine optimization, usually shortened to SEO) to increase the number of backlinks pointing to their website. Some methods are free for use by everyone whereas some methods like linkbaiting requires quite a bit of planning and marketing to work. Some websites stumble upon "linkbaiting" naturally; the sites that are the first with a tidbit of 'breaking news' about a celebrity are good examples of that. When "linkbait" happens, many websites will link to the 'baiting' website because there is information there that is of extreme interest to a large number of people.

There are several factors that determine the value of a backlink. Backlinks from authoritative sites on a given topic are highly valuable. If both sites have content geared toward the keyword topic, the backlink is considered relevant and believed to be have strong influence on the search engine rankings of the webpage granted the backlink. A backlink represents a favorable 'editorial vote' for the receiving webpage from another granting webpage. Another important factor is the anchor text of the backlink. Anchor text is the descriptive labeling of the hyperlink as it appears on a webpage. Search engine bots (i.e., spiders, crawlers, etc.) examine the anchor text to evaluate how relevant it is to the content on a webpage. Anchor text and webpage content congruency are highly weighted in search engine results page (SERP) rankings of your webpage with respect to any given keyword query by a search engine user.

Backlink

2009-07-05T09:28:00.002-07:00

Backlinks (or back-links [UK]) are incoming links to a website or web page. In the search engine optimization (SEO) world, the number of backlinks is one indication of the popularity or importance of that website or page (though other measures, such as PageRank, are likely to be more important). Outside of SEO, the backlinks of a webpage may be of significant personal, cultural or semantic interest: they indicate who is paying attention to that page.

In basic link terminology, a backlink is any link received by a web node (web page, directory, website, or top level domain) from another web node (Björneborn and Ingwersen, 2004). Backlinks are also known as incoming links, inbound links, inlinks, and inward links.

Blind link

2009-07-05T09:28:00.001-07:00

Some links are created to intentionally hide the ultimate destination of a link until the user has clicked on it. It's accomplished via redirection (possibly a URL shortening service) or client-side JavaScript. Blind links are usually used for deceptive or advertising reasons, and are most associated with TGPs and Rickrolling.

Link broker

2009-07-05T09:27:00.002-07:00

A link broker is a company that allows you to buy or rent links. Link brokerages function in a few different ways but all offer the same service: selling or renting you links. The quality of the sites, the links they sell and the prices vary greatly, as do the effects those links can have at the search engines.

Forum signature linking

2009-07-05T09:27:00.001-07:00

Forum signature linking is a technique used to build backlinks to a website. This is the process of using forum communities that allow outbound hyperlinks in their member's signature. This can be a fast method to build up inbound links to a website; it can also produce some targeted traffic if the website is relevant to the forum topic. It should be stated that forums using the nofollow attribute will have no actual Search Engine Optimization value.

Link bait

2009-07-05T09:26:00.000-07:00

Link bait is any content or feature within a website that somehow baits viewers to place links to it from other websites. Matt Cutts defines link bait as anything "interesting enough to catch people's attention."[8] Link bait can be an extremely powerful form of marketing as it is viral in nature.

Link bait in search engine optimization

The quantity and quality of inbound links are two of the many metrics used by a search engine ranking algorithm to rank a website. Link bait creation falls under the task of link building, and aims to increase the quantity of high-quality, relevant links to a website. Part of successful linkbaiting is devising a mini-PR campaign around the release of a link bait article so that bloggers and social media users are made aware and can help promote the piece in tandem. Social media traffic can generate a substantial amount of links to a single web page. Sustainable link bait is rooted in quality content.

Types of link bait

Although there are no clear-cut subdivisions within link bait, many[who?] attempt to divide them into types of hooks. This is a short list of some of the most common approaches with brief descriptions:

* Informational hooks - Provide information that a reader may find very useful. Some rare tips and tricks or any personal experience through which readers can benefit.
* News hooks - Provide fresh information and obtain citations and links as the news spreads.
* Humor hooks - Tell a funny story or a joke. A bizarre picture of your subject or mocking cartoons can also prove to be link bait.
* Evil hooks - Saying something unpopular or mean may also yield a lot of attention. Writing about something that is not appealing about a product or a popular blogger. Provide strong reasons for it.
* Tool hooks - Create some sort of tool that is useful enough that people link to it.
* Widgets hooks - A badge or tool, that can be placed or embedded on other websites, with a link included.

Link popularity

2009-07-05T09:25:00.004-07:00

Link popularity is a measure of the quantity and quality of other web sites that link to a specific site on the World Wide Web. It is an example of the move by search engines towards off-the-page-criteria to determine quality content. In theory, off-the-page-criteria adds the aspect of impartiality to search engine rankings. Link popularity plays an important role in the visibility of a web site among the top of the search results. Indeed, some search engines require at least one or more links coming to a web site, otherwise they will drop it from their index.

Search engines such as Google use a special link analysis system to rank web pages. Citations from other WWW authors help to define a site's reputation. The philosophy of link popularity is that important sites will attract many links. Content-poor sites will have difficulty attracting any links. Link popularity assumes that not all incoming links are equal, as an inbound link from a major directory carries more weight than an inbound link from an obscure personal home page. In other words, the quality of incoming links counts more than sheer numbers of them.

Free for all linking

2009-07-05T09:25:00.003-07:00

A free for all (FFA) link page is a web page set up ostensibly to improve the search engine placement of a particular web site. Webmasters typically will use software to place a link to their site on hundreds of FFA sites, hoping that the resulting incoming links will increase the ranking of their site in search engines. Experts in SEO techniques do not place much value on FFAs. First, most FFAs only maintain a small number of links for a short time, too short for most search engines to pick up. Second, the high "human" traffic to FFA sites is almost completely other webmasters visiting the site to place their own links manually. Finally, search engine algorithms count more than link numbers, they also check relevancy which the unrelated links on FFA sites do not have. Another drawback to FFAs is the amount of spam e-mail webmasters will receive from members of the FFA. Using an FFA can be considered a form of spamdexing.

Link doping

2009-07-05T09:25:00.001-07:00

Link doping refers to the practice and effects of embedding a large number of gratuitous hyperlinks on a website, in exchange for reciprocal links. Mainly used when describing blogs, link doping usually implies that a person hyperlinks to sites he or she has never visited, in return for a place on the website's blogroll, for the sole purpose of inflating the apparent popularity of his or her website. Since the search algorithms of many web directories and search engines rely on the number of hyperlinks to a website to determine its importance or influence, link doping can result in a high placement or ranking for the offending website.

Originally used in an essay published in Sobriquet Magazine and on Blogcritics.org, link doping has been confused with the related practice of excessive hyperlinking, also known as "link whoring". While the two phrases may be used interchangeably to describe gratuitous linking, link doping carries the additional connotation of deliberately striving to attain a certain level of success for one's website without having earned it through hard work (as an average athlete on steroids might perform better than a naturally gifted athlete not on performance-enhancing drugs).

Underlinking

2009-07-05T09:24:00.001-07:00

The opposites of overlinking are null linking and underlinking, which are phenomena in which hyperlinks are reduced to such a degree as to remove all pointers to a likely-needed context of an unusual term, in the text-area where the term occurs. Underlinking results whenever a reader encounters an odd term in an article (perhaps not even for the first time), and wants to briefly browse more deeply at that point, but he or she cannot without an extensive search of the article for a (possibly non-existent) instance of the linked term.

The extreme case of underlinking is a dead-end page, a page with no links at all. Usability experts discourage making dead-end pages.

Underlinking also occurs when web pages use the rel=nofollow attribute to prevent search engines from considering these links when performing link analysis, weighting or ranking.

Overlinking

2009-07-05T09:23:00.001-07:00

Overlinking in a webpage or another hyperlinked text is the characteristic of having too many hyperlinks.

It is characterized by:

* A large proportion of the words in each sentence being rendered as links.
* Links that have little information content, such as linking on specific years like 1995, or unnecessary linking of common words used in the common way, for which the reader can be expected to understand the word's full meaning in context, without any hyperlink help.
* A link for any single term is excessively repeated in the same article. "Excessive" is usually more than one link for the same term in a line or a paragraph, since in this case one or more duplicate links will almost certainly then appear needlessly on the viewer's screen.

Incestuous linking

2009-07-05T09:22:00.002-07:00

Incestuous linking is an SEO strategy used by a webmaster to promote a collection of their own web sites, or those of close friends.

Due to the domination of the search engine market by Google, and its underlying PageRank technology, sites are deemed to be more important if they have large numbers of inbound links. If those inbound links are also from highly ranked web sites, they will boost the web site further. With the take-up of blogging and social networking sites such as MySpace, this has resulted in lots of web sites that are inter-linked and can artificially improve the ranking of a web site without merit, i.e. without valuable or unique content.

When the sites are not directly owned, this is referred to as a web clique.

Link campaign

2009-07-05T09:22:00.001-07:00

Link campaigns are a form of online marketing and SEO. A business seeking to increase the number of visitors to its web site can ask its strategic partners, professional organizations, chambers of commerce, suppliers, and customers to add links from their web sites. A link campaign may involve mutual links back and forth between related sites, but it doesn't have to require the reciprocation of links.

Multi-way linking

2009-07-05T09:21:00.002-07:00

Multi-way linking is a technique used for website promotion whereby websites may create similar one-way links that each involves 3 or more partner sites. This provides each website with a one-way non-reciprocal link. This technique has evolved from reciprocal linking. According to Google and Yahoo, the latest search algorithms have evolved to hold less favor towards websites that contain a high percentage of reciprocated links, and a higher favor towards websites that maintain a high level of incoming non-reciprocated (one way) links. How to filter out excessive reciprocal link schemes is even being mentioned in anti link spam patents.

The term multi-way simply refers to the fact that the link exchange is between 3 or more websites, however each link is singular by only pointing to one other website. Other means of linking that may increase your web presence may also include other indirect methods such as loading images, videos, content or RSS feeds from a third partners website.

One-way linking

2009-07-05T09:21:00.001-07:00

One-way link is a term used among webmasters for link building methods. It is a hyperlink that points to a website without any reciprocal link; thus the link goes "one-way" in direction. It is suspected by many industry consultants that this type of link would be considered more natural in the eyes of search engines. One-way links are also called Incoming Links or Inbound Links.

An effective way to build this type of one-way linking is by distributing articles through content sites and article directories. These articles generally contain an About The Author box that contains a one-way link back to the author's URL. When publishers use these articles, those one-way links help authors increase their page rank.

Reciprocal link

2009-07-05T09:17:00.000-07:00

A reciprocal link is a mutual link between two objects, commonly between two websites to ensure mutual traffic. Example: Alice and Bob have websites. If Bob's website links to Alice's website, and Alice's website links to Bob's website, the websites are reciprocally linked. Website owners often submit their sites to reciprocal link exchange directories, in order to achieve higher rankings in the search engines. Reciprocal linking between websites is an important part of the search engine optimization process because Google uses link popularity algorithms (defined as the number of links that led to a particular page and the anchor text of the link) to rank websites for relevancy.

Relevant linking

Relevant linking is a derivative of reciprocal linking in which a site linked to another site contains only content compatible and relevant to the linked site. Relevant linking has become increasingly important because most major search engines stress that -- in Google's words -- "quantity, quality, and relevance of links count towards your rating."[1].

The engines' insistence on reciprocal links being relevant developed because many of the methods described below -- free-for-all linking, link doping, incestuous linking, overlinking, multi-way linking -- and other schemes were designed to unethically "fool" search-engines into awarding undeservedly high page ranks and/or return positions to sites engaged in search-engine spamming.

Though the engines warned site developers (again quoting from Google) to avoid "'free-for-all' links, link popularity schemes, or submitting your site to thousands of search engines (because) these are typically useless exercises that don't affect your ranking in the results of the major search engines -- at least, not in a way you would likely consider to be positive [2]" they also took proactive steps to recognize linking schemes and downrate or de-index sites using them.

This, in turn, led to the development of search-engine compliant link-management systems enabling webmasters to benefit from the upside of reciprocal linking without putting themselves and their sites at risk from inadvertently straying over into the darkside.

Since many linking schemes -- particularly those involving some form of link farming or free-for-all linking -- were (and still are) based on variations of a 1999 patent [3]for an automated system of gathering links and adding them to a website without the possibility of editorial direction or intervention, development of a solution based on a polar opposite approach became highly desirable.

In 2006, after six years of evaluating the company's application and its underlying editor-based technology for acquiring and managing links, the U.S. Patent Office awarded Creative Net Ventures of Atlanta patent #7,082,470 [4] for its LinksManager application.

To date, the LinksManager system remains the only proprietary, patented, semi-automatic link-exchange enabler to comply with all major search-engine quality guidelines and Web best practices standards.

Three way linking

See also: Webring

Three way linking (siteA ⇒ siteB ⇒ siteC ⇒ siteA) is a special type of reciprocal linking. The attempt of this link building method is to create more "natural" links in the eyes of search engines. The value of links by three-way linking can then be better than normal reciprocal links, which are usually done between two domains.

Two-Way-Linking[Link exchange]

An alternative to the automated linking above is a link exchange forum, in which members will advertise the sites that they want to get links to, and will in turn offer reciprocal or three way links back to the sites that link to them. The links generated through such services are subject to editorial review.

What is link exchange ?

2009-07-05T08:41:00.000-07:00

A link exchange (also known as a banner exchange) is a confederation of websites that operates similarly to a web ring. Webmasters register their web sites with a central organization, that runs the exchange, and in turn receive from the exchange HTML code which they insert into their web pages. In contrast to a web ring, where the HTML code simply comprises simple circular ring navigation hyperlinks, in a link exchange the HTML code causes the display of banner advertisements, for the sites of other members of the exchange, on the member web sites, and webmasters have to create such banner advertisements for their own web sites.

The banners are downloaded from the exchange. A monitor on the exchange determines, from referral information supplied by web browsers, how many times a member web site has displayed the banner advertisements of other members, and credits that member with a number of displays of its banner on some other member's web site. Link exchanges usually operate on a 2:1 ratio, such that for every two times a member shows a second member's banner advertisement, that second member displays the first member's banner advertisement. This page impressions:credits ratio is the exchange rate.

One of the earliest link exchanges was LinkExchange, a company that is now owned by Microsoft.

Link exchanges have advantages and disadvantages from the point of view of those using the World Wide Web for marketing. On the one hand, they have the advantages of bringing in a highly targeted readership (for link exchanges where all members of the exchange have similar web sites), of increasing the "link popularity" of a site with Web search engines, and of being relatively stable methods of hyperlinking. On the other hand, they have the disadvantages of potentially distracting visitors away to other sites before they have fully explored the site that the original link was on.

Feig notes several aspects of link exchange companies that prospective members take into account:

* Banners that are animated images result in member web sites taking a long time to load. Some companies impose restrictions on animation lengths.
* The size, in bytes, of a banner is important, affecting both how long it takes to load and how long it takes to render the web site displaying the banner.
* Control over the subjects of advertisements is important. Some companies offer guarantees that advertisements will be restricted to certain subjects, will not include advertisements for pornography, and so forth.
* Companies that provide mechanisms to design banners for webmasters often use automated facilities, where the generated banner design is not reviewed by a human being.