: This paper presents a systematic study of some major problems involved in the transformation of business process modelling languages to executable business process representations. A business process modelling language usually uses the simple concept of `goto' to describe the operation sequence of a business. If a structured language is chosen as the executable representation, it is difficult to compile the unstructured goto flows into structured statements when the process model is irreducible. This paper discusses a method called Regular Expression Language (REL). REL is a method that can compile a business process model that is irreducible with unstructured loops to statements in structured languages with controlled code complexity. Examples are given for compiling models expressed as UML2 Activity Diagrams into the Business Process Execution Language for Web Services (BPEL4WS).