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Parsing XSD Schema with SOM

, 13 Oct 2008 CPOL
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Pull metadata from a schema or generate XML mappers
HelloSOM.png

Introduction

This article shows how to use a Schema Object Model(SOM) navigator as an arbitrary schema. This is useful when you have a schema and want to generate your own mapping or want to build a custom XML generator or XSD based code generator.

Using the Code

First read schema and "compile", this will validate the schema.

private static XmlSchema
ReadAndCompileSchema(string fileName)
{
    XmlTextReader tr = new XmlTextReader(fileName,
                        new NameTable());

    // The Read method will throw errors encountered
    // on parsing the schema
    XmlSchema schema = XmlSchema.Read(tr,
           new ValidationEventHandler(ValidationCallbackOne));
    tr.Close();

    XmlSchemaSet xset = new XmlSchemaSet();
    xset.Add(schema);

    xset.ValidationEventHandler += new ValidationEventHandler(ValidationCallbackOne);

    // The Compile method will throw errors
    // encountered on compiling the schema
    xset.Compile();

    return schema;
}

private static void ValidationCallbackOne(object sender, ValidationEventArgs args)
{
    Console.WriteLine("Exception Severity: " + args.Severity);
    Console.WriteLine(args.Message);
}

Start traversing at the highest level...

private static void TraverseSOM(string xsfFilename)
{
    XmlSchema custSchema = ReadAndCompileSchema(xsfFilename);

    foreach (XmlSchemaElement elem in
					 custSchema.Elements.Values)
    {
        ProcessElement(elem);
    }
}

Only an element can contain attributes... so it's handled in a little special way:

private static void ProcessElement(XmlSchemaElement elem)
{
    Console.WriteLine("Element: {0}", elem.Name);

    if (elem.ElementSchemaType is XmlSchemaComplexType)
    {
	XmlSchemaComplexType ct = 
		elem.ElementSchemaType as XmlSchemaComplexType;

	foreach (DictionaryEntry obj in ct.AttributeUses)
		Console.WriteLine("Attribute: {0}  ", 
		(obj.Value as XmlSchemaAttribute).Name);

	ProcessSchemaObject(ct.ContentTypeParticle);
    }
}

Process the Choice & Sequence elements generically (this handles the type casting required):

private static void ProcessSequence(XmlSchemaSequence sequence)
{
    Console.WriteLine("Sequence");
    ProcessItemCollection(sequence.Items);
}

private static void ProcessChoice(XmlSchemaChoice choice)
{
    Console.WriteLine("Choice");
    ProcessItemCollection(choice.Items);
}

The Schema objects are processed generically, but uniformly:

private static void ProcessItemCollection(XmlSchemaObjectCollection objs)
{
    foreach (XmlSchemaObject obj in objs)
    ProcessSchemaObject(obj);
}

private static void ProcessSchemaObject(XmlSchemaObject obj)
{
    if (obj is XmlSchemaElement)
        ProcessElement(obj as XmlSchemaElement);
    if (obj is XmlSchemaChoice)
        ProcessChoice(obj as XmlSchemaChoice);
    if (obj is XmlSchemaSequence)
        ProcessSequence(obj as XmlSchemaSequence);
}

Points of Interest

There's a lot of type checking and casting. That's inherent in the data model used in the SOM. It's not a strongly typed data structure. So you have to check, cast, then use. It would be an interesting exercise to generate a strongly typed XSD model, but I'll leave that for another article.

History

  • 2008-10-10: Article created

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

CodingBruce
Engineer Big Company
United States United States
My professional career began as a developer fixing bugs on Microsoft Word97 and I've been fixing bad habits ever since. Now I do R&D work writing v1 line of business applications mostly in C#/.Net.
 
I've been an avid pilot/instructor for 13+ years, I've built two airplanes and mostly fly gliders now for fun. I commute in an all-electric 1986 BMW 325 conversion.
 
I'd like to get back to my academic roots of programming 3D analysis applications to organize complex systems.

Comments and Discussions

 
QuestionMessage Automatically Removed PinmemberDavid Harrison26-Aug-14 0:44 
QuestionLinqToXsd Update PinmemberCodingBruce6-May-12 2:31 
QuestionThanks a lot! PinmemberDanielLey18-Mar-12 12:50 
Questionparsing XSD schema Pinmemberzinazsh22-Nov-11 11:06 
AnswerRe: parsing XSD schema PinmemberCodingBruce23-Nov-11 1:23 
QuestionLinq2Xsd makes this silly PinmemberCodingBruce23-Sep-11 13:38 
GeneralThe lights go on... PinmemberGer Hayden6-Jun-11 21:09 
QuestionHow to extract Description that is within annotation tag?Please help! [modified] Pinmemberabhinavchowdhary18-May-11 10:58 
I am using your sample to parse my XSD.
 
How can we extract text value of the description tag which is within annotation tag.

I need to extract all description tag value as well for each elements present in XSD. I have a complex XSD which imports and includes other complex XSDs.
 
Would you be so kind to provide sample code.
 
Thanks in advance!

modified on Wednesday, May 18, 2011 5:06 PM

AnswerRe: How to extract Description that is within annotation tag?Please help! [modified] [modified] PinmemberRayD23-Sep-11 13:25 
QuestionProblem with nested <xs:group> Pinmemberakothoor12-Apr-11 5:38 
GeneralSchema w/LinqToXsd PinmemberCodingBruce4-Dec-10 10:07 
Generalthanks PinmemberMember 112416822-Jun-09 0:25 
GeneralThank you PinmemberMember 238152731-May-09 20:16 
GeneralThanks PinmemberJohn Irwin29-Oct-08 1:26 

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