Nowadays, it is a modern trend to develop a CASE tool for system modelling with an ability to transform models defined in different notations and also to generate a program code. However development of such a tool often involves experimentation with transformation algorithms that may require changes to the source model structure. Since CASE tools are basically used to represent a model in diagram’s form, implementing experimental changes in a modelling tool can require additional effort. In order to solve this problem, authors propose a way of describing the two-hemisphere model using Domain Specific Language. This paper covers the language’s syntax as well as provides an example of the two-hemisphere model defined with its help.