【正文】 s grasp of the PLC code. VI. CONCLUSIONS AND OUTLOOK Reengineering of PLC programs needs a formal approach to be developed. In this paper one way to solve this task is introduced. Based on a given PLC program written in Instruction List a stepwise transformation to a formal representation is proposed. Since this process will not be fully automatic, the need for flexible visualization of intermediate steps is derived. XML is presented as a flexible, standardized means to serve as data format for the description of the PLC code. The corresponding technology of XSL transformations and the Document Object Model are presented as tools for the variety of customized visualization tasks during the reengineering process. Based on the XML description of PLC programs further transformations will be applied to finally derive a pletely formalized description of the original PLC code. This will be in the form of a finite automaton. During this process it is planned to identify mon IL structures and formalize them via a library. Gaining the Benefit of the XML Metadata Interchange (XMI) as an open industry standard that applies XML to abstract systems such as UML and referring to the classification of the instructions of IL into the eleven categories mentioned above. We can extract UML classes from this classification, as it resembles the action semantics of UML. VII. AKNOWLDGMENT We would like to express gratitude to the “StiAung RheinlandPfalz fir Innovation” for sponsoring our work under project number 616. 。Logical Operation) U/Instruction /ILROW . ILRow Instruction instructionId=Jump Operation SPB/Instruction Instruction instructionId= special Operation BE/Instruction /ILROW /ILRow Fig. 2 A new transformed XML showing only the inslructions and the corresponding instruction ID E. Visualization of XML Both of the XML documents generated above can be transformed into HTML or other readable documents with the help of XSL. An ingenious XSL can be designed so as to produce an HTML which can convey the logical and other features of the PLC program in an easily conceivable form. Moreover, the DOM structure embedded in the XML， also enables the user to navigate through the PLC programs in an easy way. For the example the visualization is done in HTML. This visualization is done for the transformed XML after the validation of it39。 more recently a number of alternative languages have been proposed. The W3C XML Schema language replicates the essential functionality of DTDs, and adds a number of features: the use of XML instance syntax rather than an ad hoc notation, clear relationships between schemas and namespaces, a systematic distinction between element types and data types, and a singleinheritance form of type derivation. In other words schemas offer a richer and more powerful way of describing information than what is possible with DTDs. V. AN APPROACH FOR THE VISUALIZATION OFPLC PROGRAMS A. Overview Since Instruction List (IL) is the most monly used PLC language in Europe, the presented approach is based on this language. The proprietary IL dialect Siemens STEP 5 and the standardized version according to IEC 611313 are considered. The generation of XML documents showing different aspects of a PLC program is realized in the following three steps. of the PLC program to an XML document of the XML against the XML Schema which sets the syntax of the XML of the Instruction elements of the transformed XML according to the instruction set of the source PLC These three steps are discussed in subsections B to D respectively. Subsection E explains the visualization of the different XMLs obtained during the preceding steps. Throughout this Section an example is used to illustrate the presented concepts. Fig. 1shows a PLC code written in Instruction List Siemens S1. The PLC code is written in atabular form where each row element is either a delimited list consisting of address, label, instruction, operand and description or a ment. Kommentar : Autor Erstellt : Geaendert am: B1B:O NETZWERK 1 EMPFANGEN SLAVE 3 VON MASTER NAME :EMPE39。 and the plexity of full SGML, whose syntax allows many powerful but hardtoprogram options on the other side. While HTML describes how data should be presented, XML describes the data itself. A number of industries and scientific disciplinesmedical records and newspaper publishing among themare already using XML to exchange information across platforms and applications. XML can be tailored to describe virtually any kind of information in a form that the recipient of the information can use in a variety of ways. It is specifically designed to support information exchange between systems that use fundamentally different forms of data representation, as for example between CAD and scheduling applications. Using XML with its powerful parsers and inherent robustness in terms of syntactic and semantic grammar is more advantageous than the conventional method of using a lexical analyzer and a validating parser[7]. The conventional method of analysis of program code requires a scanner (lexical analyser) which generates a set of terminal symbols (tokens) followed by a parser that checks the grammatical structure of the code and generates an object . In the object the internal structure of the program is represented by identified objects and the relations between them. Both the sc