Define Hierarchies

Tree-like structures provide an easily visualised, and well-understood means of organising information. Hierarchies can make classification tasks much easier by presenting a content creator with a tree to browse to find the correct category rather than a flat list. The final step in the analysis of our ontology is to decide which subject types should be organised into hierarchies. In some cases you may be using subjects that have already been broken down into a hierarchy - for example a company structure is often represented as a tree and many common subject directories are also structured as trees.

Once you have determined which subject types should be organised into hierarchies, you must then decide for each hierarchy you are going to create what type of association will be used to connect parent and child items together and also what to use as the root item in the hierarchy.

Hierarchies for the Company Intranet

In our company intranet example we will create hierarchies for the Technology subject type and the Market Area subject type. In each case we are going to organise the subjects by a broader/narrower relationship. For example the technologies "XML Parsers" and "XML Editors" could share the broader technology category of "XML Tools". Similarly, the Market Area "Government" might have narrower areas "Local Government" and "National Government". In both cases we will therefore use the association type "Broader/Narrower" to connect these items into a tree. We want to keep these two trees separate and so we will create the topics "All Technologies" and "All Market Areas" to serve as the root nodes of each tree.