The environment of the manufacturing systems designer who at the early design stage is preoccupied with modelling and identification processes, is increasing in complexity. To deal with this complexity, systems analysts need to he supported in a number of areas and stages of their activities. This paper looks at the early stage of such activities that concerns decomposition of tasks and functions identifying a manufacturing system. Decomposition occurs at the highest level of abstraction and it must provide enough information for the lower level design stages where manufacturing functions are transformed into manufacturing agents that are further integrated through the flow of information into the informational model of the overall system. The proposed approach includes incorporation of logic into functional space and some elements of optimization in this space. The methodology presented is illustrated with examples.