Whilst this violates the definition of a hierarchy, it is difficult to spot. A third kind of problem involves deciding on an appropriate set of constructs. Consider an online catalogue for a motor manufacturer such as Ford. We can start with a set of vehicles and then identify subsets of different brands Ford, Volvo, Land Rover, etc. and subsets for each of these for models such as Mondeo, Range Rover, etc. But now, suppose we want to capture parts.
Some parts only work for certain models built in certain periods.
Now consider accessories. A number of software suppliers have developed products to support the creation and management of taxonomic catalogues for B2B e-commerce. Products include eMerge which allows organisations to construct an online catalogue for procurement. Suppliers load product information into eMerge, and this information is organised into a consistent structure and staged for review and approval before loading into an e-procurement catalogue. Searching an online catalogue is then via text searching, including key word searching, or tree searching.