Design Patterns for Process

By now, European companies are the market leaders in the development of process automation software. Current numbers indicate, however, that this market position is going to change in favor of US and Far East companies. This thesis can be regarded as a contribution to keep the leading market position because it presents an innovative software architecture for process automation systems which promises a high reuse factor up to 70% and therefore helps to save time and costs for the development of future process automation software. Until now, software in this domain has been developed with traditional programming languages like Fortran or C, which restrict the reuse of software to a rather low level (source code and procedure libraries), whereas object-oriented techniques even allow to reuse the whole logic of a system. Design Patterns are considered as a very popular architectural guideline in objectoriented systems because they brie y describe a common way of implementing frequently appearing problems. This thesis presents ve design patterns for di erent kinds of communication mechanisms occurring in process automation systems. They deal with the diÆculties in telegram-based communication when telegrams (data streams) are transferred between di erent operating systems. The telegrams need to be converted to the data format of the target system. In addition, the design patterns o er a general technique to distribute the contents of the (converted) telegrams; and they provide a exible, event-based architecture for data requests and commands in a distributed environment. The design patterns in this thesis have been implemented on Windows NT 4.0 with Microsoft Visual C++ 5.0 and the CORBA implementation Orbix 2.3c for inter-process communication. A special con guration mechanism, based on a selfde ned meta information concept, even increases the power of the design patterns. It enables the users to customize the software without touching the source code. The applicability of the design patterns has nally been validated by tests under real-time conditions at the hot rolling mill of VOEST-Alpine Stahl Linz AG. They all ful ll the requirements in terms of eÆciency, exibility, adaptability, reuse and portability and can henceforth be considered as a platform for the development of future process automation software.