We could classify interaction in the context of a hierarchical structure as consisting of transactions. Systems built around transactions tend to be linear, for example, the bottom line of an accounting system is the linear sum of all transactions in the organization. They tend to be reduced to a single scalar quantity, (money being the most common), to simplify the linear "roll up" process. This quantity is measured in the currency of the hierarchy, from the point of view of the hierarchy. Transactions tend to be synchronized, with much hierarchical control of which transactions occur in what sequence. A banking system is a classical example of this type of system. Banking transactions are defined in terms of money, conform to the accounting system and procedures of the bank, and are carefully monitored to insure that they are executed in the proper sequence. ATM machines are a highly visible product of this model of operation.
At the other end of the spectrum we have interaction which is based on web structures, consisting of transformations. There may be no hierarchical structure to the system at all, only browsing and explicit linking between objects which are collected in a "flat" pool. Interactions with the system cannot be characterized in a single scalar quantity, as is the case with transactional systems. The system is not linear nor synchronized, nor is it under the control of a single point of view. Observers have their own points of view--their own inverted perspective. The system as a whole becomes a complex adaptive one, evolving over time as we have seen with the WWW.
