Validating Input Xml Data Files

private void Validate()
{
XmlTextReader textReader ;
XmlValidatingReader vReader = new XmlValidatingReader(textReader);
try
{
textReader = new XmlTextReader(inputFilename);
// create a validating reader.
XmlValidatingReader vReader = new XmlValidatingReader (textReader);
// validate using the schemas stored in the schema collection.
vreader.Schemas.Add (xsc);
// set the validation event handler
vreader.ValidationEventHandler += new ValidationEventHandler
(validationCallBack);
// read and validate the XML data.
while (vreader.Read()){}
MessageBox.Show ("Validation finished. Validation {0}",
(isValid==true ? "successful": "failed"));
}
catch (Exception ex)
{
MessageBox.Show ("Exception : " + ex.Message);
}
finally
{
// close the readers, no matter what.
vreader.Close ();
textReader.Close ();
}
}

5. In the main function, write the following code :

static void Main( )
{
// would pass through since the File conforms to the schema
SchemaValidator validXmlFile = new
SchemaValidator(@"D:\Xml\ValidBooks.xml", @"D:\Xml\ books.xsd");
validXmlFile.Validate( ) ;
// would fail through since the File does not conform to the schema
SchemaValidator invalidXmlFile = new SchemaValidator (@"D:\Xml\ InvalidBooks.xml", @"D:\Xml\ books.xsd");
invalidXmlFile.Validate ( );
}

Validation using XSL Technology :

XSLT [Extended Stylesheet Language Transformation] is basically used for transforming the input xml File from one form to another, which could be .html, .xml etc. Here, we use XSLT to transform the input Xml File to a form that we require for further processing [for instance, we could transform it in a form that could be directly passed as a parameter to a Database Stored Procedure for further processing].

Note: Here, by transforming, we are actually filtering the records that satisfy a given condition.

/* In the sample example, the source file books.xml contains 2 records. On applying XSL Transformation, the Result file contains only 1 record.
Here, book records are said to be valid only if the price (one of the fields) of a book is greater than 10.00.*/

This is achieved through the following code in the .xsl file :

<xsl:template match="book">
<xsl:if test="price > 10">
<xsl:element name="title">
<xsl:value-of select="title"/>
</xsl:element>
....other sub - elements
</xsl:if>
</xsl:template>

Thus, an input Xml File can be validated not only against its schema [which is more of xml Tag validation], but also for the data that the Tags contain.

Following are the steps that need to be implemented in .Net Code for validating using .xsl file:

1. Create a Class File named DataValidator.cs

2. Include the following namespace and variables :

System.Xml
System.Xml.Schema
System.Xml.XPath
System.Xml.Xsl
System.Windows.Forms
// variable declarations
private string inputFilename ;
private string xslFilename ;
private string outputFilename ;

3. In the initializer function (could be a Constructor) , load the input xml File and the schema Files :

public DataValidator (string xmlFile, string xslFile, string outputFilename)
{
this.inputFilename = xmlFile ;
this.xslFilename = xslFile;
this.outputFilename = outputFilename;
}

4. Write a ValidateAndTransform ( ) that does the actual transformation and write the result to an output File.

public void ValidateAndTransform ( )
{
XmlTextWriter textWriter = new XmlTextWriter (this. outputFilename, null);
try
{
XPathDocument xPathDocument = new
XPathDocument (this.xmlFilename);
XslTransform xslTransform = new XslTransform ();
xslTransform.Load (this.xslFilename);
xslTransform.Transform (xPathDocument, null, textWriter);
}
catch (Exception ex)
{
MessageBox.Show ("Exception: " + ex.Message);
}
finally
{
textWriter.Close ( );
}
}

5. In the main function, write the following code :

static void Main()
{
DataValidator dataValidator = new DataValidator
(@"D:\Xml\books.xml", // source Xml File
@"D:\Xml\books.xsl", // transformation File
@"D:\Xml\result.xml") // result Xml File
dataValidator.ValidateAndTransform ();
}

The data from result.xml could subsequently be read into a string variable and sent as a parameter to a Database Stored Procedure in which using SQLXML constructs like OPENXML( ), sp_xml_preparedocument, etc we could store the resultant records into Database Tables.

Conclusion

We have currently discussed only two of the several strategies for validating the input Xml Data File. Another possible method would be to load the complete input File in a DOM object and validating each record programmatically. Every method stems out from some business requirement and/or quest parameters like technology available, timeframe, volume of data etc. Taking into consideration all the relevant parameters, one has to implement the best option which could be yet another method off the beaten track.