The method(s) and system(s) for implementing extensibility of computational design and modelling of subject area on a computational platform in respect of a new subject in a subject area through a modelling schema includes populating the new subject in the model repository as data elements corresponding to the domain entity model of the domain entity meta model. The method includes generating a subject integration layer and a subject information interaction layer from the populated subject data elements and generating GUI screens for user interactions from the populated subject data elements. The method, further, includes integrating user determined external simulation tools with the computational platform by mapping the user determined external simulation tool parameters to the subject data elements. Subsequently, the method includes generating simulation tool adapters from said mapping to achieve said integration.