Qualitative modelling of a multi-step process: The case of French breadmaking

In this paper, we investigate a problem of qualitative modelling of a multi-step food process, French breadmaking. The French breadmaking process has been represented as a sequence of steps where each step is defined through its control variables, the state variables of its output, and the causal relations between the control and state variables. In addition, the output of a step is the input of the followed step, and then, the state variables of one step depend on its control variable and the state variables of its input. A qualitative model of mixing, certainly the most complex operation of breadmaking process, has been built up. Human experts reasoning has been represented through seven cognitive operations and a qualitative algebra (Q,~,@?,@?) has been defined to model the calculation of state variables of mixed dough from the mixing control variables and the ingredients (the mixing input) condition. The relations well known by the human experts and other relevant relations between state variables of the mixed dough have been found out through the qualitative equations established. The mixing model has been implemented using the QualiS(C) expert-system shell. The score established according to French standard of the dough after the mixing step was compared to the one computed. In most of the 81 cases simulated, satisfactory results were obtained since the only unfavourable cases had never been experimented by the experts before, which finally validated this approach, thus worth to be extended to the following steps of breadmaking process.