We propose a Method Engineering Language, called MEL, as a formal representation language for the description of method fragments,
i.e. the development processes, and the products and deliverables of a systems development method. The language allows representing
the structures of method fragments, the applicable consistency rules, and a variety of method assembly operators, all of which
the semantics are formally defined. The MEL language is illustrated by a simple example of a Sequence Diagram of UML.