New approaches to production management can be conceptualized as treating production as flow rather than transformation. These alternatives can in turn be regarded as reflecting opposing ontological positions, holding respectively that reality is constituted of temporal process, or atemporal substance. The new production philosophy thus arguably represents a process ontology radically different from the atemporal metaphysics underlying conventional methods and theories. Moreover, research in physics education has identified the disjunction between ontological categories of 'substance' and 'process' as a particularly acute barrier to understanding process phenomena. Studies are presented which demonstrate the possibility of specifying and classifying mental models, with regard to two important management solutions in construction. Thus, procedures typically adopted in quantity surveying and the implementation of structural engineering design are examined. Methods of measurement used in quantity surveying are designed to account primarily for physical, rather than temporal properties. In design, the emphasis is on representing properties of finished structures, rather than the construction processes. The process is then managed by treating the design and its execution as separate products. It is argued here that alternative, more effective management solutions are derived from a process ontology.