In order to clarify the review and the discussions, we propose a model for describing and classifying the methods using five components and their corresponding elements (Fig 3). Each of the five components addresses one major aspect of the SPM methodology, and every element that results can be instantiated with its set of possible values. The first component is the modelling, i.e. what is studied and is modelled, where the goal is to describe and formalize the work domain. The second component is the data acquisition performed by human observations or by sensor systems. The third is the analysis that tries to make the link between the acquired data and the information that we want to model. Another component specifies the different applications of the systems based on SPMs and finally the last component describes the different kind of validation and evaluation studies that were conducted for assessing these systems. The whole review is organised according to diagram of Fig 3. In the following subsections, each part of the diagram is explained in detail.
