In late 2006, Google filed a new patent application that is believed to be based on the Latent Semantic Indexing (LSI) algorithm. This algorithm will index documents, identify phrases that are related to the content and then determine their relevance to subject matter of the website. This means a keyword density approach is to be modified further. With the LSI algorithm, themes which are judged from phrases hold more relevance to the search engine. Theme density or the number of related words is important with respect to the overall ranking of a website, as LSI gains prominence.

Theme Density

Since theme density cannot be restricted to only a single page, the entire website must be designed to include a linking structure based upon themes or phrases. Here's where silos come in. The silo structure can assure a web designer or search engine optimisation (SEO) firm of a measured theme density across an entire website. With a silo, easy categorisation of each sub element of the web page is possible in a hierarchical design. Phrase based information retrieval established on LSI are analytical algorithms that use thematic structures to index websites. Silos reiterate the themes that encapsulate each section, and thus guarantee a better search ranking.

The Silo Structure

Named after the grain storage structures seen across the countryside, a silo driven website design incorporates a distinction in sub themes within a website. Just as the farmyard silo will have only one particular grain stored, each different sub theme of the website has its own silo. This prevents content from mixing up and also enhances the theme of individual pages. The silo structure creates a hierarchical arrangement of web pages that are linked and optimised for Latent Semantic Analysis.

Theme Bleeding

One SEO mistake with respect to silos and themes is known as Theme Bleeding. Here one link from a page with a specific topic leads to a page with an unrelated topic or theme. SEO firms that excessively back link can jeopardise their rankings if the do not consider the effect that theme bleeding has. One way of combating this is by establishing quality back links and setting up a silo structure. The silo driven approach ensures that back links contain a degree of relevance, and thus serve as a new blueprint for SEO and site development.