【正文】 a suit of five programming languages: Instruction List (IL) is a lowlevel textual language with a structure similar to assembler. Originated in Europe IL is considered to be the PLC language in which all other IEC61 1313 languages can be translated. Ladder Diagram (LO) is a graphical language that has its roots in the USA. LDs conform to a programming style borrowed from electronic and electrical circuits for implementing control logics. Structured Text (STJ is a very powerful highlevel language. ST borrows its syntax from Pascal, augmenting it with some features from Ada. ST contains all the essential elements of a modem programming language. Function Block Diagram (FBD) is a graphical language and it is very mon to the process industry. In this language controllers are modelled as signal and data flows through function blocks. FBD transforms textual programming into connecting function blocks and thus improves modularity and software reuse. Sequential Function Chart (SFC) is a graphical language. SFC elements are defined for structuring the anization of programmable controller programs. One problem with IEC 61 1313 is that there is no standardized format for the project information in a PLC programming tool. At the moment there are only vendor specific formats. This is also one reason for the restriction of formalization approaches to single programs or algorithms. However, recently the PLC users? anization PLCopen (see started a Technical Committee to define an XML based format for projects according to IEC 611313. This new format will ease the access of formalization tools to all relevant information of a PLC project. Ⅲ . REENGINEERING APPROACH The presented approach towards reengineering (cf. ) is based upon the conception that XML can be used as a medium in which PLC codes will be transformed. This transformation offers the advantage of obtaining avendor independent specification code. (Even if the PLCopen succeeds in defining a standardized format for PLC applications, there will remain a lot of existing programs that do not conform to this standard.) Based on this code a stepwise transformation to a formal model (automata) is planned. This model can then be used for analysis, simulation, formal verification and validation, and finally for the reimplementation of the optimized algorithm on the same or another PLC. Since reengineering of plete programs will, in most cases, be only a semiautomatic process, intermediate visualization of the code is an important point. At different stages of the process different aspects of the code and/or formal model have to be visualized in a way that a designer can guide the further work. XML with its powerful visualization and transformation tools is an ideal tool for solving this task. IV. XML AS A TOOL FOR VISUALIZATION XML (extensible Markup Language) is a simple and flexible metalanguage, ， a language for describing other languages. Tailored by the World Wide Web Consortium (W3C) as a dialect of SGML [S], XML removes two constraints which were holding back Web developments [6]. The dependence on a single, inflexible document type (HTML) which was being much abused for tasks it was never designed for on one side。om the XML document shown in Fig. 7 using XSL. This visualization enables a better understanding of the PLC program. Fig. 11 shows the special visualization of instruction ids given in the XML of Fig. 6. 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. VIII. REFERENCES 1. L. Baresi, M. Mauri, A. Monti, and M. Pezze, “PLCTools: Design, Formal Validation, and Code Generation for Programmable Controllers”, in. IEEE Conference on Systems, Man, and Cybernefics (SMCZOOO), Nashville, USA, Oct. 2022, pp. 2437 2442. 2. G. Frey and L. Litz, “Formal methods in PLC programming”, in IEEE Con on Systems, Man and Cyberics (SMC’ZOOO), Nashville, USA, Oct. 2022, pp. 24312436. 3. M. Bani Younis and G. Frey, “Formalization of Existing PLC Programs: A Survey.“, in CESA 2022, Lille (France), Paper No. S2R000239, July 2022. 4. International Electrotechnical Commission, IEC International Standard 11313, Programmable Controllers, Part 3, Programming Languages, 1993. 5. World Wide Web Consortium: htfp。這表明如何 XML 和相應(yīng)的技術(shù)可用于形式化和可視化現(xiàn)有的 PLC 程序。其中一個重要的領(lǐng)域就是已經(jīng)在最近的時間成長在規(guī)范化的 PLC 程序是逆向工程 [ 3 ] 。 PLC 代碼轉(zhuǎn)型成為一個獨立的格式被確定為在這個