The notion of modelling with definitive scripts (MWDS) was introduced by Beynon in his 1985 paper Definitive Notations for Interaction ([Bey85]). This initiated the ongoing research which is known today as Empirical Modelling (EM). Over subsequent years, the range of applications for MWDS has increased, the focus of research has shifted from programming to modelling, and understanding of the essentially informal semantic foundations for MWDS has become more mature. Notwithstanding these advances, the use of special purpose definitive notations (DNs) to formulate families of definitions ("definitive scripts") remains central to the apparatus of modelling within the EM project. This thesis studies technical and theoretical aspects of DNs through the design and implementation of a new DN, C-Graph. Drawing on the experience and knowledge behind previous DNs, C-Graph is an experiment in novel DN design and implementation aimed at developing a better understanding of DNs and enhancing their applications.