Frequently asked questions about getting started with XML (4)

　How to deal with whitespace characters in the xml object model?

　 Sometimes, the XML object model will display TEXT nodes that contain whitespace characters. When whitespace characters are truncated, it's likely to cause some confusion. For example, the following XML example:

　　]>
　Smith
John

　 generates the following tree:

　PRocessing Instruction: xml
　DocType: person
　ELEMENT: person
　TEXT:
　ELEMENT: lastname
TEXT:
ELEMENT : firstname
　TEXT:

　The first name and last name are surrounded by TEXT nodes containing only whitespace characters, because the content model of the "person" element is MIXED; it contains the #PCDATA keyword. The MIXED content model specifies that text can exist between elements. Therefore, the following is also correct:

My last name is Smith and my first name is John

The result is a tree similar to the following: ELEMENT: person
TEXT: My last name is

ELEMENT : lastname

　　　TEXT: and my first name is
　　ELEMENT: firstname
　　TEXT:


　　Without the whitespace characters after and before the word "is", and the whitespace characters after and before the word "and", the sentence would not be understandable. . Therefore, for the MIXED content model, text combinations, whitespace characters, and elements are all relevant. This is not the case for non-MIXED content models.

　To make the TEXT node with only whitespace characters disappear, remove the #PCDATA keyword from the "person" element declaration:

　The result is the following clear tree:

　Processing Instruction: xml

　DocType: person

　ELEMENT: person

　　ELEMENT: lastname
　ELEMENT: firstname

　What does an XML declaration do?

　The XML declaration must be listed at the top of the XML document:

　It specifies the following items:

　The document is an XML document. MIME detectors can use this to detect if a file is of type text/xml when the MIME type is missing or has not been specified.

　The document complies with the XML 1.0 specification. This will be important in the future if there are other versions of XML.

　Document character encoding. The encoding attribute is optional and defaults to UTF-8.

　Note: The XML declaration must be on the first line of the XML document, so the following XML file:

　 produces the following parsing error:

　Invalid xml declaration.

　 Line 0000002:

Location 0000007: ------^

Note: The XML declaration is optional. If you need to specify comments or processing instructions at the top, don't put an XML declaration. However, the default encoding will be UTF-8.

　How can I print my XML document in a readable format?

　When constructing a document from scratch using DOM to produce an XML file, everything is on one line with no spaces between each other. This is the default behavior.

　Construct the default XSL stylesheet in Internet Explorer 5 to display and print XML documents in a readable format. For example, if you have IE5 installed, try looking at the nospace.xml file. The following tree should be displayed in the browser:

　　-

　-

　

　 Printing readable XML is very interesting, especially when there are DTDs that define different types of content models. For example, under the mixed content model (#PCDATA) you cannot insert spaces as it might change the meaning of the content. For example consider the following XML:

　Elephant
　This would be better not to output as:

　E

　elephant

　because the word boundaries are no longer correct.

　All of these make automated printing problematic. If you don't need to print readable XML, you can use the DOM to insert whitespace characters as text nodes at appropriate locations.

　How to use namespaces in DTD? To use a namespace in a DTD, declare it in the ATTLIST declaration of the element that uses it, as follows:

　The namespace type must be #FIXED. The same goes for attribute namespaces:

　Namespaces and XML schemas

　DTD and XML schemas cannot be mixed. For example, the following xmlns:x CDATA #FIXED "x-schema:myschema.xml" will not cause the schema definition defined in myschema.xml to be used. The use of DTD and XML schemas are mutually exclusive.

　How to use XMLDSO in Visual Basic?

Use the following XML as an example:

Mark Hanson 206 765 4583

Jane Smith 425 808 1111 You can bind to an ADO recordset as follows:

　Create a new VB 6.0 project.

　Add references to Microsoft ActiveX Data Objects 2.1 or later, Microsoft Data Adapter Library, and Microsoft XML version 2.0.

Use the following code to load XML data into the XML DSO control:

　　Dim dso As New XMLDSOControl
　　Dim doc As IXMLDOMDocument
　 Set doc = dso. ：

　　Dim da As New DataAdapter

　 Set da.Object = dso

　 Dim rs As New ADODB.Recordset
　 Set rs.DataSource = da


　 Access data:

MsgBox rs.Fields("name"). Value

　The result shows the string "Mark Hanson"
　How to use XML DOM in java?

　The IE5 version of MSXML.DLL must be installed. In Visual J++ 6.0, select Add COM Wrapper from the Project menu, and then select "Microsoft XML 1.0" from the COM object list. This will construct the required Java wrapper into a new package called "msxml". These pre-built Java wrappers are also available for download. Classes can be used as follows:

　　import com.ms.com.*;

　import msxml.*;

　public class Class1
　{
　public static void main (String[] args)
　{
　DOMDocument doc = new DOMDocument ();
　doc.load(new Variant("file://d:/samples/ot.xml"));
　System.out.println("Loaded " + doc.getDocumentElement().getNodeName());
　　}
　}

　　The code example will load the 3.8MB test file "ot.xml" from the sun religion example. The Variant class wraps the Win32 VARIANT basic type.

　You cannot use pointer comparisons on nodes because you actually get a new wrapper every time you retrieve a node. So instead of using the following code,

IXMLDOMNode root1 = doc.getDocumentElement(); IXMLDOMNode root2 = doc.getDocumentElement(); if (root1 == root2)...

Code:

　if (ComLib.isEqualUnknown(root1, root2)) ....

　 . The total size of the .class wrapper is approximately 160KB. However, for full compliance with the W3C specification, only IXMLDOM* wrappers should be used. The following classes are old IE 4.0 XML interfaces and can be removed from the msxml folder:

　_xml_error*

　This reduces the size to 147KB. You can also delete the following items:


　DOMFreeThreadedDocument
　Access XML documents from multiple threads in Java applications.
　xmlhttpRequest
　Use the XML DAV HTTP extension to communicate with the server.

　IXTLRuntime

　 Define XSL stylesheet script object.

　XMLDSOControl

　Bind to XML data in an HTML page.

　XMLDOMDocumentEvents

　Return callbacks during the analysis process.



　This reduces the size to 116KB. To make it smaller, consider the fact that the DOM itself has two layers: The core layer consists of:


　　DOMDocument, IXMLDOMDocument
　IXMLDOMNode*
　IXMLDOMNodeList*
　IXMLDOMNamedNodeMap*

　IXMLDOMDocumentFragment*

　IXMLDO MImplementation

　 IXMLDOMParseError

　 and users may need to retain DTD information:


　IXMLDOMDocumentType
IXMLDOMEntity
IXMLDOMNotation

All node types in an XML document are IXMLDOMNodes, which provide full functionality, but there are higher-level wrappers for each node type. Therefore, if you modify the DOMDocument wrapper and change these specific types to use IXMLDOMNode, then all the following interfaces can be removed: IXMLDOMAttribute IXMLDOMCDATASection IXMLDOMCharacterData IXMLDOMComment ProcessingInstruction

IXMLDOMEntityReference
IXMLDOMText

Deleting these will Reduce the size to 61KB. However, for IXMLDOMElement, both the getAttribute and setAttribute methods are useful. Otherwise, you need to use:

　IXMLDOMNode.getAttributes().setNamedItem(...)

The above is the content of the FAQ (4) for getting started with XML. For more related content, please pay attention to the PHP Chinese website (m.sbmmt.com) !