Compilando esquemas XML

As classes no namespace System.Xml.Schema mapeiam para as estruturas definidas na recomendação do W3C (World Wide Web Consortium) sobre esquemas XML e podem ser usadas para compilar esquemas XML na memória.

Compilando um esquema XML

Nos exemplos de código a seguir, a API do SOM é usada para compilar um esquema XML cliente na memória.

Criando o elemento e os atributos

Os exemplos de código compilam o esquema cliente de baixo para cima, criando primeiro elementos e atributos filho, bem como seus tipos correspondentes, e depois os elementos de nível superior.

No exemplo de código a seguir, os elementos FirstName e LastName, bem como o atributo CustomerId do esquema cliente são criados usando as classes XmlSchemaElement e XmlSchemaAttribute do SOM. Com exceção das propriedades Name das classes XmlSchemaElement e XmlSchemaAttribute, que correspondem ao atributo "name" dos elementos <xs:element /> e <xs:attribute /> em um esquema XML, todos os outros atributos permitidos pelo esquema (defaultValue, fixedValue, form e assim por diante) têm propriedades correspondentes nas classes XmlSchemaElement e XmlSchemaAttribute.

// Create the FirstName and LastName elements.
XmlSchemaElement^ firstNameElement = gcnew XmlSchemaElement();
firstNameElement->Name = "FirstName";
XmlSchemaElement^ lastNameElement = gcnew XmlSchemaElement();
lastNameElement->Name = "LastName";

// Create CustomerId attribute.
XmlSchemaAttribute^ idAttribute = gcnew XmlSchemaAttribute();
idAttribute->Name = "CustomerId";
idAttribute->Use = XmlSchemaUse::Required;

// Create the FirstName and LastName elements.
XmlSchemaElement firstNameElement = new XmlSchemaElement();
firstNameElement.Name = "FirstName";
XmlSchemaElement lastNameElement = new XmlSchemaElement();
lastNameElement.Name = "LastName";

// Create CustomerId attribute.
XmlSchemaAttribute idAttribute = new XmlSchemaAttribute();
idAttribute.Name = "CustomerId";
idAttribute.Use = XmlSchemaUse.Required;

' Create the FirstName and LastName elements.
Dim firstNameElement As XmlSchemaElement = New XmlSchemaElement()
firstNameElement.Name = "FirstName"
Dim lastNameElement As XmlSchemaElement = New XmlSchemaElement()
lastNameElement.Name = "LastName"

' Create CustomerId attribute.
Dim idAttribute As XmlSchemaAttribute = New XmlSchemaAttribute()
idAttribute.Name = "CustomerId"
idAttribute.Use = XmlSchemaUse.Required

Criando tipos de esquema

O conteúdo de elementos e de atributos é definido pelos respectivos tipos. Para criar elementos e atributos cujos tipos são um dos tipos internos do esquema, a propriedade SchemaTypeName das classes XmlSchemaElement ou XmlSchemaAttribute são definidas com o nome qualificado correspondente do tipo interno usando a classe XmlQualifiedName. Para criar um tipo definido pelo usuário de elementos e atributos, um novo tipo simples ou complexo é criado usando a classe XmlSchemaSimpleType ou XmlSchemaComplexType.

Observação

Para criar tipos simples ou complexos sem nome que sejam filhos anônimos de um elemento ou atributo (somente os tipos simples são aplicáveis a atributos), defina a propriedade SchemaType das classes XmlSchemaElement ou XmlSchemaAttribute como o tipo simples ou complexo sem nome, em vez da propriedade SchemaTypeName das classes XmlSchemaElement ou XmlSchemaAttribute.

Os esquemas XML permitem que tipos simples, anônimos e nomeados, sejam derivados pela restrição de outros tipos simples (internos ou definidos pelo usuário) ou construídos como uma lista ou união de outros tipos simples. A classe XmlSchemaSimpleTypeRestriction é usada para criar um tipo simples restringindo o tipo interno xs:string. Você também pode usar as classes XmlSchemaSimpleTypeList ou XmlSchemaSimpleTypeUnion para criar tipos de lista ou de união. A propriedade XmlSchemaSimpleType.Content indica se é uma união, uma lista ou uma restrição de tipos simples.

No exemplo de código a seguir, o tipo do elemento FirstName é o tipo interno xs:string, o tipo do elemento LastName é um tipo simples nomeado que é uma restrição do tipo interno xs:string, com um valor de faceta MaxLength igual a 20, e o tipo do atributo CustomerId é o tipo interno xs:positiveInteger. O elemento Customer é um tipo complexo anônimo cuja partícula é a sequência dos elementos FirstName e LastName e cujos atributos contêm o atributo CustomerId.

Observação

Você também pode usar as classes XmlSchemaChoice ou XmlSchemaAll como partícula do tipo complexo para replicar as semânticas <xs:choice /> ou <xs:all />.

// Create the simple type for the LastName element.
XmlSchemaSimpleType^ lastNameType = gcnew XmlSchemaSimpleType();
lastNameType->Name = "LastNameType";
XmlSchemaSimpleTypeRestriction^ lastNameRestriction =
    gcnew XmlSchemaSimpleTypeRestriction();
lastNameRestriction->BaseTypeName =
    gcnew XmlQualifiedName("string", "http://www.w3.org/2001/XMLSchema");
XmlSchemaMaxLengthFacet^ maxLength = gcnew XmlSchemaMaxLengthFacet();
maxLength->Value = "20";
lastNameRestriction->Facets->Add(maxLength);
lastNameType->Content = lastNameRestriction;

// Associate the elements and attributes with their types.
// Built-in type.
firstNameElement->SchemaTypeName =
    gcnew XmlQualifiedName("string", "http://www.w3.org/2001/XMLSchema");
// User-defined type.
lastNameElement->SchemaTypeName =
    gcnew XmlQualifiedName("LastNameType", "http://www.tempuri.org");
// Built-in type.
idAttribute->SchemaTypeName = gcnew XmlQualifiedName("positiveInteger",
    "http://www.w3.org/2001/XMLSchema");

// Create the top-level Customer element.
XmlSchemaElement^ customerElement = gcnew XmlSchemaElement();
customerElement->Name = "Customer";

// Create an anonymous complex type for the Customer element.
XmlSchemaComplexType^ customerType = gcnew XmlSchemaComplexType();
XmlSchemaSequence^ sequence = gcnew XmlSchemaSequence();
sequence->Items->Add(firstNameElement);
sequence->Items->Add(lastNameElement);
customerType->Particle = sequence;

// Add the CustomerId attribute to the complex type.
customerType->Attributes->Add(idAttribute);

// Set the SchemaType of the Customer element to
// the anonymous complex type created above.
customerElement->SchemaType = customerType;

// Create the simple type for the LastName element.
XmlSchemaSimpleType lastNameType = new XmlSchemaSimpleType();
lastNameType.Name = "LastNameType";
XmlSchemaSimpleTypeRestriction lastNameRestriction =
    new XmlSchemaSimpleTypeRestriction();
lastNameRestriction.BaseTypeName =
    new XmlQualifiedName("string", "http://www.w3.org/2001/XMLSchema");
XmlSchemaMaxLengthFacet maxLength = new XmlSchemaMaxLengthFacet();
maxLength.Value = "20";
lastNameRestriction.Facets.Add(maxLength);
lastNameType.Content = lastNameRestriction;

// Associate the elements and attributes with their types.
// Built-in type.
firstNameElement.SchemaTypeName =
    new XmlQualifiedName("string", "http://www.w3.org/2001/XMLSchema");
// User-defined type.
lastNameElement.SchemaTypeName =
    new XmlQualifiedName("LastNameType", "http://www.tempuri.org");
// Built-in type.
idAttribute.SchemaTypeName = new XmlQualifiedName("positiveInteger",
    "http://www.w3.org/2001/XMLSchema");

// Create the top-level Customer element.
XmlSchemaElement customerElement = new XmlSchemaElement();
customerElement.Name = "Customer";

// Create an anonymous complex type for the Customer element.
XmlSchemaComplexType customerType = new XmlSchemaComplexType();
XmlSchemaSequence sequence = new XmlSchemaSequence();
sequence.Items.Add(firstNameElement);
sequence.Items.Add(lastNameElement);
customerType.Particle = sequence;

// Add the CustomerId attribute to the complex type.
customerType.Attributes.Add(idAttribute);

// Set the SchemaType of the Customer element to
// the anonymous complex type created above.
customerElement.SchemaType = customerType;

' Create the simple type for the LastName element.
Dim lastNameType As XmlSchemaSimpleType = New XmlSchemaSimpleType()
lastNameType.Name = "LastNameType"
Dim lastNameRestriction As XmlSchemaSimpleTypeRestriction = _
    New XmlSchemaSimpleTypeRestriction()
lastNameRestriction.BaseTypeName = _
    New XmlQualifiedName("string", "http://www.w3.org/2001/XMLSchema")
Dim maxLength As XmlSchemaMaxLengthFacet = New XmlSchemaMaxLengthFacet()
maxLength.Value = "20"
lastNameRestriction.Facets.Add(maxLength)
lastNameType.Content = lastNameRestriction

' Associate the elements and attributes with their types.
' Built-in type.
firstNameElement.SchemaTypeName = _
    New XmlQualifiedName("string", "http://www.w3.org/2001/XMLSchema")
' User-defined type.
lastNameElement.SchemaTypeName = _
    New XmlQualifiedName("LastNameType", "http://www.tempuri.org")
' Built-in type.
idAttribute.SchemaTypeName = New XmlQualifiedName("positiveInteger", _
    "http://www.w3.org/2001/XMLSchema")

' Create the top-level Customer element.
Dim customerElement As XmlSchemaElement = New XmlSchemaElement()
customerElement.Name = "Customer"

' Create an anonymous complex type for the Customer element.
Dim customerType As XmlSchemaComplexType = New XmlSchemaComplexType()
Dim sequence As XmlSchemaSequence = New XmlSchemaSequence()
sequence.Items.Add(firstNameElement)
sequence.Items.Add(lastNameElement)
customerType.Particle = sequence

' Add the CustomerId attribute to the complex type.
customerType.Attributes.Add(idAttribute)

' Set the SchemaType of the Customer element to
' the anonymous complex type created above.
customerElement.SchemaType = customerType

Criando e compilando esquemas

Neste ponto, os elementos e atributos filho, seus tipos correspondentes e o elemento de nível superior Customer foram criados na memória usando a API do SOM. No exemplo de código a seguir, o elemento de esquema é criado usando a classe XmlSchema, os elementos e os tipos de nível superior são adicionados a ele usando a propriedade XmlSchema.Items e o esquema completo é compilado usando a classe XmlSchemaSet e criado no console.

// Create an empty schema.
XmlSchema^ customerSchema = gcnew XmlSchema();
customerSchema->TargetNamespace = "http://www.tempuri.org";

// Add all top-level element and types to the schema
customerSchema->Items->Add(customerElement);
customerSchema->Items->Add(lastNameType);

// Create an XmlSchemaSet to compile the customer schema.
XmlSchemaSet^ schemaSet = gcnew XmlSchemaSet();
schemaSet->ValidationEventHandler += gcnew ValidationEventHandler(ValidationCallback);
schemaSet->Add(customerSchema);
schemaSet->Compile();

for each (XmlSchema^ schema in schemaSet->Schemas())
{
    customerSchema = schema;
}

// Write the complete schema to the Console.
customerSchema->Write(Console::Out);

// Create an empty schema.
XmlSchema customerSchema = new XmlSchema();
customerSchema.TargetNamespace = "http://www.tempuri.org";

// Add all top-level element and types to the schema
customerSchema.Items.Add(customerElement);
customerSchema.Items.Add(lastNameType);

// Create an XmlSchemaSet to compile the customer schema.
XmlSchemaSet schemaSet = new XmlSchemaSet();
schemaSet.ValidationEventHandler += new ValidationEventHandler(ValidationCallback);
schemaSet.Add(customerSchema);
schemaSet.Compile();

foreach (XmlSchema schema in schemaSet.Schemas())
{
    customerSchema = schema;
}

// Write the complete schema to the Console.
customerSchema.Write(Console.Out);

' Create an empty schema.
Dim customerSchema As XmlSchema = New XmlSchema()
customerSchema.TargetNamespace = "http://www.tempuri.org"

' Add all top-level element and types to the schema
customerSchema.Items.Add(customerElement)
customerSchema.Items.Add(lastNameType)

' Create an XmlSchemaSet to compile the customer schema.
Dim schemaSet As XmlSchemaSet = New XmlSchemaSet()
AddHandler schemaSet.ValidationEventHandler, AddressOf ValidationCallback
schemaSet.Add(customerSchema)
schemaSet.Compile()

For Each schema As XmlSchema In schemaSet.Schemas()
    customerSchema = schema
Next

' Write the complete schema to the Console.
customerSchema.Write(Console.Out)

O método XmlSchemaSet.Compile valida o esquema cliente em relação às regras de um esquema XML e disponibiliza as propriedades de pós-compilação de esquema.

Observação

Todas as propriedades de pós-compilação de esquema na API do SOM diferem do conjunto de informações de pós-validação de esquema.

O objeto ValidationEventHandler adicionado à classe XmlSchemaSet é um delegado que chama o método de retorno de chamada ValidationCallback para tratar avisos e erros de validação de esquema.

Veja a seguir o exemplo de código completo e o esquema cliente criado no console.

#using <System.Xml.dll>

using namespace System;
using namespace System::Xml;
using namespace System::Xml::Schema;

ref class XmlSchemaCreateExample
{
public:

    static void Main()
    {
        // Create the FirstName and LastName elements.
        XmlSchemaElement^ firstNameElement = gcnew XmlSchemaElement();
        firstNameElement->Name = "FirstName";
        XmlSchemaElement^ lastNameElement = gcnew XmlSchemaElement();
        lastNameElement->Name = "LastName";

        // Create CustomerId attribute.
        XmlSchemaAttribute^ idAttribute = gcnew XmlSchemaAttribute();
        idAttribute->Name = "CustomerId";
        idAttribute->Use = XmlSchemaUse::Required;

        // Create the simple type for the LastName element.
        XmlSchemaSimpleType^ lastNameType = gcnew XmlSchemaSimpleType();
        lastNameType->Name = "LastNameType";
        XmlSchemaSimpleTypeRestriction^ lastNameRestriction =
            gcnew XmlSchemaSimpleTypeRestriction();
        lastNameRestriction->BaseTypeName =
            gcnew XmlQualifiedName("string", "http://www.w3.org/2001/XMLSchema");
        XmlSchemaMaxLengthFacet^ maxLength = gcnew XmlSchemaMaxLengthFacet();
        maxLength->Value = "20";
        lastNameRestriction->Facets->Add(maxLength);
        lastNameType->Content = lastNameRestriction;

        // Associate the elements and attributes with their types.
        // Built-in type.
        firstNameElement->SchemaTypeName =
            gcnew XmlQualifiedName("string", "http://www.w3.org/2001/XMLSchema");
        // User-defined type.
        lastNameElement->SchemaTypeName =
            gcnew XmlQualifiedName("LastNameType", "http://www.tempuri.org");
        // Built-in type.
        idAttribute->SchemaTypeName = gcnew XmlQualifiedName("positiveInteger",
            "http://www.w3.org/2001/XMLSchema");
        
        // Create the top-level Customer element.
        XmlSchemaElement^ customerElement = gcnew XmlSchemaElement();
        customerElement->Name = "Customer";

        // Create an anonymous complex type for the Customer element.
        XmlSchemaComplexType^ customerType = gcnew XmlSchemaComplexType();
        XmlSchemaSequence^ sequence = gcnew XmlSchemaSequence();
        sequence->Items->Add(firstNameElement);
        sequence->Items->Add(lastNameElement);
        customerType->Particle = sequence;
        
        // Add the CustomerId attribute to the complex type.
        customerType->Attributes->Add(idAttribute);

        // Set the SchemaType of the Customer element to
        // the anonymous complex type created above.
        customerElement->SchemaType = customerType;
        
        // Create an empty schema.
        XmlSchema^ customerSchema = gcnew XmlSchema();
        customerSchema->TargetNamespace = "http://www.tempuri.org";

        // Add all top-level element and types to the schema
        customerSchema->Items->Add(customerElement);
        customerSchema->Items->Add(lastNameType);

        // Create an XmlSchemaSet to compile the customer schema.
        XmlSchemaSet^ schemaSet = gcnew XmlSchemaSet();
        schemaSet->ValidationEventHandler += gcnew ValidationEventHandler(ValidationCallback);
        schemaSet->Add(customerSchema);
        schemaSet->Compile();
        
        for each (XmlSchema^ schema in schemaSet->Schemas())
        {
            customerSchema = schema;
        }

        // Write the complete schema to the Console.
        customerSchema->Write(Console::Out);
    }

    static void ValidationCallback(Object^ sender, ValidationEventArgs^ args)
    {
        if (args->Severity == XmlSeverityType::Warning)
            Console::Write("WARNING: ");
        else if (args->Severity == XmlSeverityType::Error)
            Console::Write("ERROR: ");

        Console::WriteLine(args->Message);
    }
};

int main()
{
    XmlSchemaCreateExample::Main();
    return 0;
}

using System;
using System.Xml;
using System.Xml.Schema;

class XmlSchemaCreateExample
{
    static void Main(string[] args)
    {
        // Create the FirstName and LastName elements.
        XmlSchemaElement firstNameElement = new XmlSchemaElement();
        firstNameElement.Name = "FirstName";
        XmlSchemaElement lastNameElement = new XmlSchemaElement();
        lastNameElement.Name = "LastName";

        // Create CustomerId attribute.
        XmlSchemaAttribute idAttribute = new XmlSchemaAttribute();
        idAttribute.Name = "CustomerId";
        idAttribute.Use = XmlSchemaUse.Required;

        // Create the simple type for the LastName element.
        XmlSchemaSimpleType lastNameType = new XmlSchemaSimpleType();
        lastNameType.Name = "LastNameType";
        XmlSchemaSimpleTypeRestriction lastNameRestriction =
            new XmlSchemaSimpleTypeRestriction();
        lastNameRestriction.BaseTypeName =
            new XmlQualifiedName("string", "http://www.w3.org/2001/XMLSchema");
        XmlSchemaMaxLengthFacet maxLength = new XmlSchemaMaxLengthFacet();
        maxLength.Value = "20";
        lastNameRestriction.Facets.Add(maxLength);
        lastNameType.Content = lastNameRestriction;

        // Associate the elements and attributes with their types.
        // Built-in type.
        firstNameElement.SchemaTypeName =
            new XmlQualifiedName("string", "http://www.w3.org/2001/XMLSchema");
        // User-defined type.
        lastNameElement.SchemaTypeName =
            new XmlQualifiedName("LastNameType", "http://www.tempuri.org");
        // Built-in type.
        idAttribute.SchemaTypeName = new XmlQualifiedName("positiveInteger",
            "http://www.w3.org/2001/XMLSchema");

        // Create the top-level Customer element.
        XmlSchemaElement customerElement = new XmlSchemaElement();
        customerElement.Name = "Customer";

        // Create an anonymous complex type for the Customer element.
        XmlSchemaComplexType customerType = new XmlSchemaComplexType();
        XmlSchemaSequence sequence = new XmlSchemaSequence();
        sequence.Items.Add(firstNameElement);
        sequence.Items.Add(lastNameElement);
        customerType.Particle = sequence;

        // Add the CustomerId attribute to the complex type.
        customerType.Attributes.Add(idAttribute);

        // Set the SchemaType of the Customer element to
        // the anonymous complex type created above.
        customerElement.SchemaType = customerType;

        // Create an empty schema.
        XmlSchema customerSchema = new XmlSchema();
        customerSchema.TargetNamespace = "http://www.tempuri.org";

        // Add all top-level element and types to the schema
        customerSchema.Items.Add(customerElement);
        customerSchema.Items.Add(lastNameType);

        // Create an XmlSchemaSet to compile the customer schema.
        XmlSchemaSet schemaSet = new XmlSchemaSet();
        schemaSet.ValidationEventHandler += new ValidationEventHandler(ValidationCallback);
        schemaSet.Add(customerSchema);
        schemaSet.Compile();

        foreach (XmlSchema schema in schemaSet.Schemas())
        {
            customerSchema = schema;
        }

        // Write the complete schema to the Console.
        customerSchema.Write(Console.Out);
    }

    static void ValidationCallback(object sender, ValidationEventArgs args)
    {
        if (args.Severity == XmlSeverityType.Warning)
            Console.Write("WARNING: ");
        else if (args.Severity == XmlSeverityType.Error)
            Console.Write("ERROR: ");

        Console.WriteLine(args.Message);
    }
}

Imports System.Xml
Imports System.Xml.Schema

Class XmlSchemaCreateExample

    Shared Sub Main()

        ' Create the FirstName and LastName elements.
        Dim firstNameElement As XmlSchemaElement = New XmlSchemaElement()
        firstNameElement.Name = "FirstName"
        Dim lastNameElement As XmlSchemaElement = New XmlSchemaElement()
        lastNameElement.Name = "LastName"

        ' Create CustomerId attribute.
        Dim idAttribute As XmlSchemaAttribute = New XmlSchemaAttribute()
        idAttribute.Name = "CustomerId"
        idAttribute.Use = XmlSchemaUse.Required

        ' Create the simple type for the LastName element.
        Dim lastNameType As XmlSchemaSimpleType = New XmlSchemaSimpleType()
        lastNameType.Name = "LastNameType"
        Dim lastNameRestriction As XmlSchemaSimpleTypeRestriction = _
            New XmlSchemaSimpleTypeRestriction()
        lastNameRestriction.BaseTypeName = _
            New XmlQualifiedName("string", "http://www.w3.org/2001/XMLSchema")
        Dim maxLength As XmlSchemaMaxLengthFacet = New XmlSchemaMaxLengthFacet()
        maxLength.Value = "20"
        lastNameRestriction.Facets.Add(maxLength)
        lastNameType.Content = lastNameRestriction

        ' Associate the elements and attributes with their types.
        ' Built-in type.
        firstNameElement.SchemaTypeName = _
            New XmlQualifiedName("string", "http://www.w3.org/2001/XMLSchema")
        ' User-defined type.
        lastNameElement.SchemaTypeName = _
            New XmlQualifiedName("LastNameType", "http://www.tempuri.org")
        ' Built-in type.
        idAttribute.SchemaTypeName = New XmlQualifiedName("positiveInteger", _
            "http://www.w3.org/2001/XMLSchema")

        ' Create the top-level Customer element.
        Dim customerElement As XmlSchemaElement = New XmlSchemaElement()
        customerElement.Name = "Customer"

        ' Create an anonymous complex type for the Customer element.
        Dim customerType As XmlSchemaComplexType = New XmlSchemaComplexType()
        Dim sequence As XmlSchemaSequence = New XmlSchemaSequence()
        sequence.Items.Add(firstNameElement)
        sequence.Items.Add(lastNameElement)
        customerType.Particle = sequence

        ' Add the CustomerId attribute to the complex type.
        customerType.Attributes.Add(idAttribute)

        ' Set the SchemaType of the Customer element to
        ' the anonymous complex type created above.
        customerElement.SchemaType = customerType

        ' Create an empty schema.
        Dim customerSchema As XmlSchema = New XmlSchema()
        customerSchema.TargetNamespace = "http://www.tempuri.org"

        ' Add all top-level element and types to the schema
        customerSchema.Items.Add(customerElement)
        customerSchema.Items.Add(lastNameType)

        ' Create an XmlSchemaSet to compile the customer schema.
        Dim schemaSet As XmlSchemaSet = New XmlSchemaSet()
        AddHandler schemaSet.ValidationEventHandler, AddressOf ValidationCallback
        schemaSet.Add(customerSchema)
        schemaSet.Compile()

        For Each schema As XmlSchema In schemaSet.Schemas()
            customerSchema = schema
        Next

        ' Write the complete schema to the Console.
        customerSchema.Write(Console.Out)
    End Sub

    Shared Sub ValidationCallback(ByVal sender As Object, ByVal args As ValidationEventArgs)
        If args.Severity = XmlSeverityType.Warning Then
            Console.Write("WARNING: ")
        Else
            If args.Severity = XmlSeverityType.Error Then
                Console.Write("ERROR: ")
            End If
        End If
        Console.WriteLine(args.Message)
    End Sub
End Class

<?xml version="1.0" encoding="utf-8"?>  
<xs:schema xmlns:tns="http://www.tempuri.org" targetNamespace="http://www.tempuri.org" xmlns:xs="http://www.w3.org/2001/XMLSchema">  
   <xs:element name="Customer">  
      <xs:complexType>  
         <xs:sequence>  
            <xs:element name="FirstName" type="xs:string" />  
            <xs:element name="LastName" type="tns:LastNameType" />  
         </xs:sequence>  
         <xs:attribute name="CustomerId" type="xs:positiveInteger" use="required" />  
      </xs:complexType>  
   </xs:element>  
   <xs:simpleType name="LastNameType">  
      <xs:restriction base="xs:string">  
         <xs:maxLength value="20" />  
      </xs:restriction>  
   </xs:simpleType>  
</xs:schema>  

Confira também

• Visão geral do modelo de objeto de esquema XML
• Lendo e gravando esquemas XML
• Percorrer esquemas XML
• Esquemas XML de edição
• Incluindo ou importando um esquema XML
• XmlSchemaSet para compilação de esquema
• Compilação Infoset de pré esquema