SAX or Simple API for XML, is an alternative to DOM, and can be used to parse (and also create) XML documents.
SAX is based on streaming model. The SAX parser reads input XML stream and generates various parsing events
that an application can handle. With each parsing event, the parser sends sufficient information about
the node being parsed. Unlike DOM, SAX does not build an in-memory representation of the source XML document, and
hence it is an excellent alternative when parsing large XML documents, as SAX does not require that much memory (and
resources). MSXML supports SAX 2.0.
Tip: Chapter 6 [Simple API for XML (SAX) in MSXML] in the book XML Application Development with MSXML 4.0 covers MSXML SAX features in great details. Dianne Arrow (Wrox Press) wrote an excellent review about this chapter.
Let's now look at how to use MSXML 4.0 SAX in Visual Basic.
The following XML document (c:\profits.xml) is used in the examples in this section. The SAX example scans this
XML documents and print the name and profit amount of the zone with the highest profit.
<?xml version="1.0" encoding="UTF-8"?>
<Profits>
<East>20000</East>
<West>28000</West>
<North>13000</North>
<South>11000</South>
</Profits>
Visual Basic
Start Visual Basic 6.0 and create a new Standard EXE project. Click on Project | Add Class Module and
rename the class from Class1 to SAXContHandlerImpl. Click on Project | References and add a reference
to Microsoft XML, v4.0 (MSXML4.DLL). Write following lines at the beginning of the class module:
Option Explicit
Option Explicit
Implements IVBSAXContentHandler
Public High_Amount As Double
Private CurAmount_Val As Double
Public HighProfit_Zone As String
Private Sub IVBSAXContentHandler_startDocument()
High_Amount = -1
HighProfit_Zone = ""
End Sub
Private Sub IVBSAXContentHandler_characters(strChars As String)
On Error Resume Next
CurAmount_Val = CDbl(strChars)
On Error GoTo 0
End Sub
Private Sub IVBSAXContentHandler_endElement(strNamespaceURI As String, strLocalName As String, strQName As String)
If CurAmount_Val > High_Amount Then
High_Amount = CurAmount_Val
HighProfit_Zone = strLocalName
End If
End Sub
Dim objReader As New MSXML2.SAXXMLReader40
Dim CHandler As New SAXContHandlerImpl
Set objReader.contentHandler = CHandler
objReader.parseURL "c:\profits.xml"
MsgBox CHandler.High_Amount
MsgBox CHandler.HighProfit_Zone
MSXML SAX Resources Around the Web
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