True relationship between parent and child

I recently had to make a change to our taxonomy search. Our previous search would match a selected node and all its children. However, we found a need to search and just match a node and not any of its child nodes. I have seen this feature in many other systems, but we never found the need to implement it in our system till recently. This highlights a deeper question of what do we expect the relationship between parent and child nodes. When we first developed our taxonomy, we had long heated discussions on this issue for our industry tree. Let's take an example of a well known software company, Oracle. Under our software category we have operating systems, business applications, desktop applications, database systems, email systems, graphics applications, etc. Oracle is a big software company that makes all kinds of software, but does not create all the types of software under our software category, but they do most. One of our team members suggested that if a company is categorized as something then it must do all the subcategories. His suggestion was to categorize multiple times for each type of product it does exactly. However, it starts get ugly when a company like Oracle is operating in most of the subcategories but not all. Our general consensus was to categorize a company in the parent category if it covers a good portion of the subcategories, but not all. If the company covers a few of the subcategories, then we will have multiple categorizations. The real key is consistency. We take the approach (and near cliche) that the parent is something different than the sum of its children.