Defining a language formally, we can profit from the advantages
offered by formal methods: unambiguity, preciseness, abstractness;
but looking at formal semantics for existing languages they are quite
often unstructured, bulky and therefore nearly incomprehensible.
But understanding a language definition is the major prerequisite for
using it and also extending or connecting the language with other
languages and language concepts.
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A theory of formal language engineering shall be motivated which should
help to solve the problems encountered. Principles known from software
engineering -- as e.g. modularity -- will be applied to formal theories
to allow a language to be defined based on it's kernel (emphasising the
elementary notions) and to be extended in a consistent way. Some notions
and techniques for language semantics based on the categorical structure
of monads allowing us to achieve the goal will be presented. The problems
are investigated in the area of state-based and concurrent systems.