Types of Navigation Systems
A complex web site often includes several types of navigation systems. To design a successful site, it is essential to understand the types of systems and how they work together to provide flexibility and context.
Hierarchical Navigation Systems
Although we may not typically think of it this way, the information hierarchy is the primary navigation system. From the main page to the destination pages that house the actual content, the main options on each page are taken directly from the hierarchy. The hierarchy is extremely important, but also rather limiting. It is these limitations that often require additional navigation systems.
Global Navigation Systems
A global or site-wide navigation system often complements the information hierarchy by enabling greater vertical and lateral movement throughout the entire site. At the heart of most global navigation systems are some standard rules that dictate the implementation of the system at each level of the site. The simplest global navigation system might consist of a graphical navigation bar at the bottom of each page on the site. On the main page, the bar might be unnecessary, since it would duplicate the primary options already listed on that page. On second level pages, the bar might include a link back to the home page and a link to the feedback facility
Local Navigation Systems
For a more complex web site, it may be necessary to complement the global navigation system with one or more local navigation systems. To understand the need for local navigation systems, it is necessary to understand the concept of a sub-site For example, a software company may provide an online product catalog as one area in their web site. This product catalog constitutes a sub-site within the larger web site of the software company. Within this sub-site area, it makes sense to provide navigation options unique to the product catalog, such as browsing products by name or format or market.
Relationships between content items do not always fit neatly into the categories of hierarchical, global, and local navigation. An additional category of ad hoc links is more editorial than architectural. Typically an editor or content specialist will determine appropriate places for these types of links once the content has been placed into the architectural framework of the web site. In practice, this usually involves representing words or phrases within sentences or paragraphs (i.e., prose) as embedded hypertext links. This approach can be problematic if these ad hoc links are important, since usability testing shows "a strong negative correlation between embedded links (those surrounded by text) and user success in finding information." Apparently, users tend to scan pages so quickly that they often miss these less conspicuous links. You can replace or complement the embedded link approach with external links that are easier for the user to see.