Though, in some situations it is necessary to drop this condition and allow some elements to appear in multiple branches The choice of categories also needs consideration. Normally, in taxonomies, each category is chosen so that there is the highest possible degree of resemblance between members of the category, though this may need to be off-set against having the maximum distinctiveness from members of other categories. Often identifying a prototypical example of a member of a category is a helpful tool. A prototypical example has all the attributes that one would expect of a member of the category, and normally is an example that can be easily articulated. For the birds, we could use blackbirds, but not penguins.
Prototypes are important when there are multiple participants involved in developing a taxonomy.
The prototypical example does not even have to be a member of the set - it is just a tool to help conceptualise the category. They are also helpful is explaining a taxonomy to users. Within e-business, taxonomies are implicitly or explicitly the subject of much deliberation at the development stage of more complex websites. Any site that gives users a number of routes through the site to a particular destination should be managed consistently so that updates take account of inter-dependencies. A common ontology, based on a taxonomy, can help both the content managers and the users to be clear about the inter-dependencies between terms.