Research on the Application of XML in Fault Diagnosis IETM

Extensible markup language (XML) [3,4,5] is a meta markup language. It is an effective tool designed to transmit and store data depending on some rules and applications. It is flexible, simple and easy to expand. Users can use any tag to define XML instance document [6]. An XML instance document contains elements and attributes. The document body has three parts: preface, body and end, which are respectively composed of multiple element nodes. Each element node has its own attributes and can expand child nodes. The writing of XML document is essentially to organize each element node reasonably. XML integrates data reuse, data display separation, scalability, syntax freedom and structured integrated data. It has unique advantages in data storage and management, powerful super connection, cross platform, cross network, cross program language data description, efficient organization of a large amount of data and so on. Of course, XML also has some disadvantages. For example, it allows users to develop tags with different rules according to needs. Although it makes the search easier and flexible, it also increases the complexity of documents, and the same data will occupy more space than stored in other style databases [7]. Therefore, when applying XML to IETM, we should take comprehensive consideration and reasonably define tags.

XML documents need to follow several basic rules when editing, including having and only one root element node; If each element node has a start tag, it must have an end tag; Each element node should be reasonably contained in the parent element and cannot be cross referenced; In order to make the creation of an element meaningful, the attribute of an element cannot be empty. In addition to the basic rules that need to be followed, when creating XML documents, appropriate schemas should be selected to describe and restrict their document structure. For this purpose, XML provides two schemas: document type definition (DTD) and XML schema. DTD [8] is a set of syntax rules about markers. It defines the logical structure of the document and specifies the elements, entities, attributes of elements and the relationship between elements and entities used in the document. XML schema [9] is the successor of DTD. It improves the shortcomings of DTD, such as non-extensibility, non-compliance with XML syntax, non-support for namespace applications, support for a few simple data types, etc. XML schema is the standard schema recommended by W3C at present, and is gradually becoming the mainstream schema of XML description and binding document structure. The analysis and comparison of the two are shown in Table I. Through the analysis and comparison of the two, XML schema itself provides a more standardized and complete mechanism to restrict an XML file than DTD, which has obvious advantages. Therefore, in the description process, this paper selects XML scheme schema to describe and restrict the XML document structure.

XML DOM, fully known as XML document object model, is a standard model for XML documents. It defines the standards and methods of accessing and operating XML documents. XML DOM regards the whole XML document as a node tree, in which each component is defined as a node that can be accessed and processed. In the XML DOM node tree shown in Figure 2, each node is independent and related to each other.

Figure 2.

Figure 3.

For example, when the user accesses the XML element and the attributes of any node in the XML document, the user can access the XML element or delete the attributes of any node through JavaScript. XML DOM is a powerful tool for users to operate XML documents. It can not only arbitrarily control the content of the whole XML document, which brings great flexibility to the development of fault diagnosis IETM, but also plays an important role in the integration and transformation between relational database and XML [10].

IETM includes various technical information such as equipment function, performance, operation principle, program, operation, maintenance, detection, inspection, fault report and exception handling, disassembly procedure, assembly... Which need to be stored [10], and then display pictures, words and other information on the electronic screen for users to consult and browse [11]. S1000D standard stipulates that technical information is organized by data module (DM), which is the smallest information unit in IETM technical data. S1000D standard defines 13 types of DM, as shown in figure 3, among which 8 types of DM are commonly used.

What may be needed in fault diagnosis IETM include description information data module, maintenance step information module, fault information data module, maintenance plan data module, etc. The data module consists of two parts: Identification and status segment(IDSTATUS) and Content segment(CONTENT). The Identification and status part is used to identify and control the data module, which is mainly used to identify and locate the data module. This part is invisible to the user. The data module code (DMC) and the version number of the data module constitute the unique identification of the data module, which is used to manage the data module in CSDB. The content part describes most of the information that users can view in the data module. This paper mainly takes the creation of fault information data module as an example to describe the role of XML in the creation of data module.

The fault information data module is an information collection that gives specific fault finding and troubleshooting methods according to different fault causes during the design and use of the equipment. It is used to describe the phenomenon, cause, relevant information of fault parts, brief solutions or detailed fault isolation procedures. It is the main basis for the fault diagnosis IETM system to realize the fault diagnosis function. The fault information data module is divided into three parts: reference information, fault report information and fault isolation procedure. Among them, the fault report describes the fault content, fault isolation describes the troubleshooting of the fault, and the reference information is used to quote other technical data. The constituent elements of each part of the fault information data module are shown in Figure 4.

Figure 4.

In order to meet the principle of “Edit once, reuse” and avoid the uncertainty of user-defined labels, when creating the fault information data module, XML stipulates that there are specific element labels to describe the information of each part of the module, in which the fault report is divided into the following four categories: isolated faults described by element <ifault>; Detected faults described by element <dfault>; Observed faults described by element <ofault>; Associated faults described with element <cfault>. Fault isolation information describes the fault information and gives the basic steps of fault isolation, which is described by element <afi>. Fault isolation information includes various information elements describing fault isolation diagnosis. This part is the focus of studying equipment fault information model and the inevitable factor to improve the success rate of fault reasoning task [12]. The final generated data module is a complete XML file. Figure 5 shows the breakdown.xml of fault information data module document fragment.

Figure 5.

When creating the fault information data module, this paper selects the XML scheme mode for breakdown Generate file breakdown.xsd, Figure 6 is the description form of fault information data module in schema mode.

Figure 6.

When using, you need to add a pattern reference to the header of the generated fault information data module:

Because XML schema itself is an XML document, and the basic syntax rules of defining document structure through XML are consistent, the created data module can be shared and used in multiple IETM systems.

Because XML documents can customize labels, have no information to display data, and separate data from display styles, corresponding technologies are needed to display information to users. XML can be displayed using Cascading style sheet (CSS), Extensible style sheet language transformations (XSLT) and scripting language JavaScript. For the breakdown.xml in Chapter 2 uses three methods as follows.

1) Using CSS style sheets: Cascading style sheet (CSS) is a computer language used to represent file styles such as HTML or XML. It can not only modify the web page statically, but also format the elements of the web page dynamically with various scripting languages. There are two ways to use CSS to control the display format of XML. One is to directly use CSS style by embedding <html: style> in the XML document. You must first define the namespace of HTML like “http://www.w3.org/TR/REC-html40” before you can use the tags in HTML The syntax is shown in Figure 7.

Figure 7.

The second is to break down the tags in the XML file CSS file. Some code examples of CSS file are as follows:

ifault {background-color: #ffffff;width: 100%;}

Then link the CSS file to the XML file, so that the tags in the XML document can display with breakdown.css file.

Compared with the first method, this method is more flexible and convenient. It can not only apply CSS files to multiple XML documents, but also write the label styles of multiple XML documents in one CSS file to realize one-time generation and reuse.

2) Using XSLT style sheets: XSLT is a language used to transform one XML document into another XML document or other types of documents. The principle is to convert the XML file into a document that can be recognized by the browser, such as HTML, before the browser displays it. When using it, you need to generate breakdown.xsl file, The code fragment is shown in Figure 8.

Figure 8.

And through the breakdown.xml add The following code:

<?xml-stylesheet type="text/xsl" href="breakdown.xsl"?>

3) Use JavaScript to dynamically display: This method mainly uses the XMLHttpRequest object to parse the XML document into the XML DOM object, and then operate the DOM object through JavaScript to obtain the information in the XML document and display it. The specific method is to define a new XMLHttpRequest object through the xmlhttp = new xmlhttprequest() operation. When the system adopts the server centered B / S structure, the XMLHttpRequest object can be used to exchange data with the server in the background, and then send a request to the server using the open() and send() methods of the XMLHttpRequest object. The method is xmlhttp.open("GET","breakdown.xml",false);xmlhttp.send(); "breakdown.xml" in the open () method is the address of the XML document on the server, and finally xmldoc = xmlhttp.responseXML; Use the responsexml attribute to return the XML document object. At this time, you can use JavaScript to manipulate the methods and attributes of the DOM node tree to check and parse the object. For example, x = xmldoc getElementsByTagName("ifault"); Locate the tag name in the XML document through the getElementsByTagName () method to obtain the content in the tag.

In the above three methods, general XSLT is the preferred XML style sheet language, and its display control flow is shown in Figure 9. During display, the required data module and its corresponding XSLT style are sent to the reader for display, and the XSLT style written in a certain mode has certain universality and can be reused.

Figure 9.

The interactive fault reasoning mechanism can adjust the user's fault symptom input as the premise part of the diagnosis rules, and then match the knowledge base. If the matching is successful, the action part of the rules will be executed until the diagnosis conclusion is reached or the rule base is exhausted. Or write the internal logical relationship of the question into the XML document, analyze, reason and judge the user's answer to the previous question to put forward the next question, and get the final diagnosis conclusion in this cycle. In the above two mechanisms, the diagnostic rules, knowledge base information and problems involved in reasoning can be described in the form of XML and displayed in the style in Chapter 3.1 when necessary.

There is a core concept in S1000D standard - common source database (CSDB). As a container for storing information and management information in IETM system, CSDB stores all the information required by the technical manual, including data modules. The data modules mentioned above are composed of XML documents, so that XML documents can be accessed through the database. At the same time, pictures, videos, audio and other data are also stored in the database, and the information in the database can be referenced in the XML document, Therefore, it is very important to select an appropriate mapping model from XML to database [15–16] to realize the mutual transformation between XML documents and database data. Using table mode, there are two main forms of conversion between XML document and database.

1) The transformation from XML document to database: parses the label in XML document into the form of table and inserts it into the database. Starting from the root node in XML document, take the label information as the attribute in the table until the last label in XML document is traversed. The attribute field definition of each tag in the database is shown in the table II. To take the <breakdown> tag in the breakdown.xml document as an example. The XML document number starts from 1 and the tag number starts from 1. Then the fields in the <breakdown> tag corresponding table have XmlID = 1, LableID = 1, LabelName = "breakdown". At the same time, two tag types are defined in XML, one is the element tag element and the other is the attribute tag attribute. Here, breakdown is the element tag, so LabelType = "element". The tag does not contain text information, and LabelVal = null. Because < breakdown > is the root node, there are no parent tags, but only child tags, so LabelParent = 0 and LabelChild = 1. By analogy, in this way, the label data in the XML document is mapped to the data in the database for storage, and the information in the XML document can be obtained by accessing the table from the database.

2) The mapping from database information to XML document: That can create an XML document for each table in the database, take the table name as the root node of the XML document, generate the sub elements under the root node with the information in the table in behavioral units, and a row of information is a sub element node, and then associate the fields in each row of information as the sub elements or attributes of the sub nodes, and the attributes of the fields as the attributes of the sub element labels. When XML schema is used to constrain the structure of XML document, it shall be consistent with the field type defined in the database. For example, if the data type of field x defined in the database table is integer, only numbers shall be used for the text of label <x> in XML document. In this way, a label node is generated in the XML document until the last field of the last row of information in the table.