XML Parser Version 2.6 and Version 3.0

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The XML parser version 2.6 and version 3.0 extend the older version that came with Internet Explorer 5. The XML parser version 2.6 is a separate DLL (Msxml2.dll) that can be installed in addition to the original XML parser. Various options are available for running the two DLLs together, but those options are beyond the scope of this book. You can check the XML SDK 2.5 (which can be viewed on Microsoft's Web site) for more information about the DLLs. Version 3.0 of the parser is installed as a new DLL (Msxml3.dll) with new version-dependent CLSIDs and ProgIDs to protect those applications that use Msxml.dll or Msxml2.dll and allow you to choose the version of the parser to use in your code.

Version 2.6 comes with five additional XML document objects: XMLDOMDocument2, XMLDOMSchemaCache, XMLDOMSelection, XMLDOMXSLProcessor, and XMLDOMXSLTemplate. We will discuss the XMLDOMXSLTemplate and XMLDOMXSLProcessor objects in Chapter 12 when we discuss XSL. Version 3.0 doesn't add any new features to version 2.6. Thus, we'll have a detailed discussion about the XMLDOMDocument2, XMLDOMSchemaCache, and XMLDOMSelection objects in the following section.

XMLDOMDocument2, XMLDOMSchemaCache, and XMLDOMSelection Objects

The XMLDOMDocument2 object implements the IXMLDOMDocument2 interface. This interface is an extension of the IXMLDOMDocument interface that supports schema caching and validation. The IXMLDOMDocument2 interface inherits all the original properties and methods of the IXMLDOMDocument interface and adds the following new properties:

Extended IXMLDOMDocument2 Properties

Name	Description
namespaces	Returns a list of all of the namespaces in the document as an XMLDOMSchemaCollection(schemaCache object)
schemas	Locates all the schema documents using the XMLDOMSchemaCollection (schemaCache object)

The XMLSchemaCache object which implements the IXMLDOMSchemaCollection interface contains information about the schemas and namespaces used by an XML document. This interface has the following property and methods:

IXMLDOMSchemaCollection Property

Name	Description
length	Returns the number of namespaces that are currently in the collection

IXMLDOMSchemaCollection Methods

Name	Description
add (namespaceURI, schema)	Adds a new schema to the schema collection. The specified schema is associated with the given namespace URI.
addCollection (XMLDOMSchemaCollection)	Adds all the schemas from another collection into the current collection.
get (namespaceURI)	Returns a read-only DOM node containing the <Schema> element.
namespaceURI (index)	Returns the namespace for the specified index.
remove (namespaceURI)	Removes the specified namespace from the collection.

Now that we've examined the properties and methods in the IXMLDOMDocument2 interface and the IXMLDOMSchemaCollection interface, it's time to see how they are used in the application. Create a new Visual Basic Standard EXE project, and name the default form frmTestDOM2. In the form frmTestDOM2, place a command button with the name cmdSchemas and the caption Schemas. Place the following code in the click event handler of this button:

 Private Sub cmdSchemas_Click() Dim objXMLDoc As DOMDocument26 Dim objXMLSchemas As XMLSchemaCache Dim lngSchemaCounter As Long Set objXMLDoc = New DOMDocument objXMLDoc.async = False objXMLDoc.Load ("c:\Books.xml") Set objXMLSchemas = objXMLDoc.namespaces For lngSchemaCounter = 0 To objXMLSchemas.length - 1 Debug.Print "URL: " & _ objXMLSchemas.namespaceURI(lngSchemaCounter) Debug.Print "Type: " & _ objXMLDoc.selectSingleNode("//author").dataType Next Set objXMLSchemas = Nothing Set objXMLDoc = Nothing End Sub 

This application loads the Books.xml document that contains a reference to the Books.dtd. If you run this program and click the Schemas button when the XML document is referencing the DTD, you will get the following result:

 URL: www.northwindtraders.com/PO Type: 

Looking back at the original XML document, you have the following two lines of code:

 <!DOCTYPE northwind:BOOKS SYSTEM "c:\Books.dtd"> <northwind:BOOKS xmlns: northwind ="www.northwind.com/PO"> 

You can see that the !DOCTYPE declaration defined the location of the DTD. Because XML documents are aware of namespaces, the parser recognized that the prefix northwind was a namespace prefix for the BOOKS element. In the next line of code, the parser finds the declaration that associates a namespace with that name and with that declaration. There is no data type information in the result above because this is a DTD.

We will now use a BizTalk schema instead of a DTD. Create the following schema file called Books.xsd:

 <Schema name="BOOKS" xmlns="urn:schemas-microsoft-com:xml-data" xmlns:dt="urn:schemas-microsoft-com:datatypes"> <ElementType name="BOOKS" content="eltOnly" model="closed"> <element type="item"/> </ElementType> <ElementType name=" item" content="eltOnly" model="closed"> <element type="title"/> <element type="author"/> <element type="price"/> <element type="quantity"/> </ElementType> <ElementType name="title" content="mixed" model="closed"> <AttributeType name="language" dt:type="string"/> <attribute type="language"/> </ElementType> <ElementType name="author" content="textOnly" model="closed" dt:type="string"/> <ElementType name="price" content="textOnly" model="closed" dt:type="string"/> <ElementType name="quantity" content="textOnly" model="closed" dt:type="string"/> </Schema> 

Create a new XML document called Books2.xml and add the following code:

 <?xml version="1.0" ?> <northwind:BOOKS xmlns:northwind="x-schema:c:\Books.xsd"> <northwind:item> <northwind:title language="English">Number, the Language of Science</northwind:title> <northwind:author>Danzig</northwind:author> <northwind:price>5.95</northwind:price> <northwind:quantity>3</northwind:quantity> </northwind:item> </northwind:BOOKS> 

Notice that to get a reference to the schema we must use x-schema in the namespace declaration. The x-schema syntax is used by Internet Explorer 5 to identify where the schema is. The namespace prefix had to be added to all the elements in order for this code to work. While that should not have been necessary, errors would result if the namespace prefix was not added. This is a reminder that the way things are implemented might not always be what you expect. Finally, change the Visual Basic code so that it references Books2.xml and the namespace prefix is included in the XSL statement:

 Private Sub cmdSchemas_Click() Dim objXMLDoc As DOMDocument26 Dim objXMLSchemas As XMLSchemaCache Dim lngSchemaCounter As Long Set objXMLDoc = New DOMDocument objXMLDoc.async = False objXMLDoc.Load ("c:\Books2.xml") Set objXMLSchemas = objXMLDoc.namespaces For lngSchemaCounter = 0 To objXMLSchemas.length - 1 Debug.Print "URL: " & _ objXMLSchemas.namespaceURI(lngSchemaCounter) Debug.Print "Type: " & objXMLDoc.selectSingleNode & _ ("//northwind:author").dataType Next End Sub 

After you make the changes, running the program and clicking the Schemas button will result in the following output:

 URL: x-schema:c:\Books.xsd Type: string 

As you can see, we get the data type information this time because the schema contains the data type information.

The XMLDOMSelection object represents a list of nodes that match an XSL pattern or an XPath expression. The XMLDOMSelection object can be created by using the selectNodes method of the IXMLDOMDocument2 interface that is included in version 2.6 and later of Microsoft XML parser. This object implements the IXMLDOMSelection interface, which inherits from the IXMLDOMNodeList interface. In Visual Basic, the XMLDOMSelection object can be used as follows:

 Dim objXMLDoc As DOMDocument26 Dim objXMLSelection As IXMLDOMSelection Set objXMLDoc = New DOMDocument26 objXMLDoc.async = False objXMLDoc.Load ("C:\Books.xml") Set objXMLSelection = objXMLDoc.selectNodes("//item [quantity=3]") Debug.Print objXMLSelection.expr 

In this example, we select the item element that has an attribute with a value of 3. The expr property of IXMLDOMSelection is used to retrieve the XPath expression string. In this case, "//item [quantity=3]" is returned.