[[File:OPM Model 2.jpg|thumb|upright=1.5|OPM model structure—OPL]]
OPM model is a metamodel, as shown in the image of OPM model on the right. Using OPM to specify the structure of an OPM model of a system. It depicts the conceptual aspects of OPM as parallel hierarchies of the graphic and textual OPM modalities and their correspondence to produce equivalent model expressions. An OPD Construct is the graphical expression of the corresponding textual OPL Sentence, which express the same model fact. An OPD and its corresponding OPL Paragraph are collections of model facts that a modeller places into the same model context.
