Indexing has always been considered a highly targeted science. Enter a search query into Google search and the pages that are displayed are generally optimized towards that exact word or term. However, in their continual battle to server the most relevant but most natural pages with genuinely useful information Google has injected latent semantic indexing (LSI) into its algorithms.
What Is LSI?
LSI is a unique indexing method that potentially takes Google search one step closer to becoming human in its way of thinking. If we were to manually search through web pages to find information related to a given search term we would be likely to generate our own results based on the theme of the site, rather than whether a word exists or doesn't exist on the page.
Why Search Engines Might Adopt Latent Semantic Indexing
The extremely rigid form of "keyword indexing" also meant that black hat SEO techniques were easier to implement. Search engines could be manipulated into ranking a site highly by using set formula. Originally, cramming a page with a particular keyword or set of keywords meant a site would rank highly for that search term. The proceeding set of algorithms ensured that your link profile played more of an important part than your keyword density. Reciprocal linking soon followed once again making it possible to manipulate the search engine spiders by exchanging links with tens, hundreds, or thousands of websites.
Reciprocal linking was soon beaten as Google and to a lesser extent Yahoo and MSN gave less credence to a reciprocal link as they did to a one-way inbound link. Latent Semantic Indexing is another, particularly powerful, method to try and make their result pages appear more natural with natural pages filled with natural content.
The introduction of LSI has seen some dramatic changes in the search engine result pages already. Sites that had previously performed well because of an impressive link profile based on a single keyword have found their pages slip in the rankings. Other pages with a more diverse portfolio of inbound links are taking the lead with search terms for which they had not previously performed.
SEO is far from dead because of LSI, in fact if anything, it has probably increased the need for professional white-hat SEO on your website. The field of SEO, though, has almost certainly changed. Website content copywriting for Google's benefit is not merely made up of keyword density and keyword placement as it once was and link-building techniques will need to change to incorporate LSI algorithms but it can be done.
Writing Content For LSI
If optimizing solely for Google then a web page can, theoretically, be naturally written and naturally worded. When we write we instinctively include the appropriate keyword in our text. In order to avoid repetition (or keyword optimization, as it was once called) we would often alter some instances of these keywords for other words with the same or very similar meaning. We naturally include the plural or singular form of a keyword as well as different tenses and a number of different stems of that keyword. In the eyes of LSI algorithms this is all good news.
Looking At Your Link Profile
A link profile should no longer consist of thousands of links with the same anchor text (that of your primary keyword). There's no reason to panic if you already have this kind of profile. Instead you should look at relevant and similar terms and improve your link profile by gaining links using these as your anchor text.
What It Offers Web Searchers
From the point of view of web searchers, LSI offers some distinct advantages over its earlier form of indexing. For example, LSI recognizes that the word "engine" in "search engine optimization" is not related to searches for terms like "steam engine" or "locomotive engine" and is instead related to Internet marketing topics. In theory, LSI results give a much more accurate page of results as well as providing a broader range of pages still geared towards a particular topic.
Where Google Leads, Others Generally Follow
It is widely acknowledged that Google is the search engine at the forefront of latent semantic indexing. On the whole they try to generate results pages that are literally filled with genuine, useful results and LSI certainly provides another string in their bow. Yahoo and MSN, for now, seem more than happy to go along with keyword specific indexing although Yahoo are known to look at singular and plural keyword variations as well as keyword stemming when judging keyword density.
The Effect On Your Website
How it affects the individual Webmaster is dependent on how they go about promoting their site already. If the pages are filled with natural content including keywords and keyword alternatives, and the link profile is similarly diversified for a number of related keywords then the fact is it won't change very much. However, if all of your efforts have been concentrated, either on-page or off-page, with a single keyword then it's time to readdress the balance.