Abstract: A computer based modelling system includes a computer processor and a memory for storing a model database. A set of primitives is stored in the database. An interface coupled to the computer processor enables a user to input, retrieve and manipulate data within the database. A high level user of the modelling system creates a modelling methodology by editing the database to define: (a) modelling objects in terms of the primitives, (b) modes of viewing the modelling objects, and (c) logical relationships between elements of the views and the modelling objects. A system modeler can create models for specific applications by selecting views representative of modelling objects stored in the database, and manipulating the views in accordance with the methodology defined by the system tooler. Invalid manipulations are prohibited. Policies of coordination can be established among a plurality of modeling sessions of one or more low level users.