(机械专业)外文翻译可视化的plc程序使用xml.doc

Visualization of PLC Programs using XML

M. Bani Younis and G. Frey

Juniorprofessorship Agentenbased Automation

University of Kaiserslautem

P. 0. Box 3049, D-67653 Kaiserslautem, Germany

Abstract - Due to the growing complexity of PLC programs there is an increasing

interest in the application of formal methods in this area. Formal methods allow rigid

proving of system properties in verification and validation. One way to apply formal

methods is to utilize a formal design approach in PLC programming. However, for

shown how XML and corresponding technologies can be used for the formalization

and visualization of an existing PLC program.

I. INTRODUCTION

Programmable Logic Controllers (PLCs) are a special type of computers that are

used in industrial and safety critical applications. The purpose of a PLC is to control a

particular process, or a collection of processes, by producing electrical control signals

in response to electrical process- related inputs signals. The systems controlled by

PLCs vary tremendously, with applications in manufacturing, chemical process

control, machining, transportation, power distribution, and many other fields.

Automation applications can range in complexity from a simple panel to operate the

modules requires a formal approach to be developed [I]. Ensuring the high quality

demands requires verification and validation procedures as well as analysis and

simulation of existing systems to be carried out [2]. One of the important fields for the

formalization of PLC programs that have been growing up in recent time is

Reverse-engineering [3]. Reverse Engineering is a process of evaluating something to

understand how it works in order to duplicate or enhance it. While the reuse of PLC

codes is being established as a tool for combating the complexity of PLC programs,

Reverse Engineering is supposed to receive increased importance in the coming years

especially if exiting hardware has to be replaced by new hardware with different

programming environments

The paper is structured as follows. First, a short introduction to PLCs and the

programs is introduced. The transformation of the PLC code into a vendor

independent format is identified as an important first step in this process. XML and

corresponding technologies such as XSL and XSLT that can be used in this

transformation are presented in Section IV. Section V presents the application of

XML for the visualization of PLC programs and illustrates the approach with an

example. The final Section summarizes the results and gives an outlook on future

work in this ongoing project.

Ⅱ PLC AND IEC 61131

Since its inception in the early ‘70s the PLC received increasing attention due to

its success in fulfilling the objective of replacing hard-wired control equipments at

machines. Eventually it grew up as a distinct field of application, research and

But in order to enhance compatibility, openness and interoperability among different

products as well as to promote the development of tools and methodologies with

respect to a fixed set of notations the IEC 61131 standard evolved. The third part of

this standard defines a suit of five programming languages:

Instruction List (IL) is a low-level textual language with a structure similar to

assembler. Originated in Europe IL is considered to be the PLC language in which all

other IEC61 131-3 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.

function blocks and thus improves modularity and software reuse.

Sequential Function Chart (SFC) is a graphical language. SFC elements are

defined for structuring the organization of programmable controller programs.

One problem with IEC 61 131-3 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

define an XML based format for projects according to IEC 61131-3. This new format

Ⅲ. RE-ENGINEERING APPROACH

The presented approach towards re-engineering (cf. Fig.1) 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

Since re-engineering of complete programs will, in most cases, be only a

semi-automatic 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 meta-language, i.e，

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

document type (HTML) which was being much abused for tasks it was never

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.

of using a lexical analyzer and a validating parser (cf. Fig. 2, [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 net. In the object

net the internal structure of the program is represented by identified objects and the

relations between them. Both the scanner and the parser to be used in this method are

The XML based method is advantageous, since the lexical specification is an

invariant component of XML; therefore the well-formedness is independent from the

respective individual application.

Hence, an XML-Parser also can transfer well-shaped XML documents in an

abstract representation called Document Object Model (DOM) without using a

grammar. DOM is an application programming interface (APII) for valid HTML and

well-formed XML documents. It defines the logical structure of documents and the

way a document is accessed and manipulated. In the DOM specification, the term

and much of this would traditionally be seen as data rather than as documents.

XSLT, the transformation language for XML is capable of transforming XML

not only to another XML or HTML but to many other user-friendly formats. Before

the advent of XSLT, the transformation of XML to any other format was only

possible through custom applications developed in a procedural language such as C++,

Visual Basic or, Java. This procedure lacked the generality with respect to the

declarative language [9].

XSLT functions in two steps. In the first step, it performs a structural

transformation so as to convert the XML into a structure that reflects the desired

output. The second stage is formatting the new structure into the required format, such

attractive visualization of a program.

a Document Type Definition (DTD) or an XML Schema. The rules defined in a DTD

or an XML Schema state the hierarchical and structural constraints of the XML

document.

The DTD is for defining the document grammars; more recently a number of