System engineering modeling formalisms and languages are made of two parts:

• An underlying mathematical model, that is capturing some aspect of the behavior of the system, e.g. differential equations for Modelica and Matlab-Simulink, Data-Flow equations for Lustre, Guarded Transition Systems for AltaRica.
• A structuring paradigm that makes it possible to build models by assembling parts (usually copied from libraries of reusable components) into hierarchical descriptions. E.g. Modelica is an object-oriented formalism. This structural part is usually flattened/compiled before the actual treatments take place.

S2ML is a freely available, prototype oriented modeling language that aims at providing a necessary and sufficient set of concepts to describe functional and/or physical structures of systems and to structure models.

To know more about S2ML:

• S2ML Specification (version 1.0).
• S2ML presentation (version 1.0).