5.1.2.2 Formulate root definitions

In order to construct an activity model, we need a statement describing the activity system to be modelled. This description is the root definition (RD), i.e. the description of what the system does, how and why. This is known as the PQR formula: do P (what), by Q (how), in order to help achieve R (why). The root definition is written out as a statement modelling a transformation process.

Although the PQR formula helps to define the root definition, which is the basis for the activity model, it can be further enriched by the use of the mnemonic CATWOE. The idea is that purposeful activity, defined by a transformation process (T) and a worldview (W) will require people (A) to do the activities which make up T. It will affect people (C) outside itself who are its beneficiaries or victims. It will take as given various constraints from the environment outside itself (E). It could be changed or stopped by persons (O) who are regarded as owning it.

• C  customers
• A  actors
• T transformation
• W  worldview
• O owners
• E  environmental constraints