Linköping University Electronic Press

Modelica is an open standardized language used for modeling and simulation of complex physical systems. The language speci cation defines a formal concrete syntax; but the semantics is informally described using natural language. The latter makes the language hard to interpret; maintain and reason about; which affect both tool development and language evolution. Even if a completely formal semantics of the Modelica language can be seen as a natural goal; it is a well- known fact that defining understandable and concise formal semantics specifications for large and complex languages is a very hard problem. In this paper; we will discuss different aspects of formulating a Modelica specification; both in terms of what should be specified and how it can be done. Moreover; we will further argue that a "middle-way" strategy can make the specification both clearer and easier to reason about. A proposal is outlined; where the current informally specified semantics is complemented with several context-sensitive grammars; specifying intermediate representations of abstract syntax. We believe that this kind of evolutionary strategy is easier to gain acceptance for; and is more realistic in the short-term; than a revolutionary approach of using a fullyformal semantics definition of the language.