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XmlSchemaSet Class

Note: This class is new in the .NET Framework version 2.0.

Contains a cache of XML Schema definition language (XSD) schemas.

Namespace: System.Xml.Schema
Assembly: System.Xml (in system.xml.dll)

Public Class XmlSchemaSet
Dim instance As XmlSchemaSet

public class XmlSchemaSet
public class XmlSchemaSet

In System.Xml version 1.0, XML schemas were loaded into an XmlSchemaCollection class as a library of schemas. In System.Xml version 2.0, the XmlValidatingReader and the XmlSchemaCollection classes are obsolete, and have been replaced by the Create method and the XmlSchemaSet class, respectively.

The XmlSchemaSet has been introduced to fix a number of issues, including standards compatibility, performance, and the obsolete Microsoft XML-Data Reduced (XDR) schema format.

The following is a comparison between the XmlSchemaCollection class and the XmlSchemaSet class.



Supports Microsoft XDR and W3C XML schemas.

Only supports W3C XML schemas.

Schemas are compiled when the Add method is called.

Schemas are not compiled when the Add method is called. This provides a performance improvement during creation of the schema library.

Each schema generates an individual compiled version that can result in “schema islands.” As a result, all includes and imports are scoped only within that schema.

Compiled schemas generate a single logical schema, a “set” of schemas. Any imported schemas within a schema that are added to the set are directly added to the set themselves. This means that all types are available to all schemas.

Only one schema for a particular target namespace can exist in the collection.

Multiple schemas for the same target namespace can be added as long as there are no type conflicts.

Security Considerations

  • External namespaces or locations referenced in include, import, and redefine elements of a schema are resolved with respect to the base URI of the schema that includes or imports them. For example, if the base URI of the including or importing schema is empty or a null reference (Nothing in Visual Basic), the external locations are resolved with respect to the current directory. The XmlUrlResolver class is used to resolve external schemas by default. To disable resolution of include, import, and redefine elements of a schema, set the XmlResolver property to a null reference (Nothing in Visual Basic).

  • The XmlSchemaSet class uses the System.Text.RegularExpressions.Regex class to parse and match regular expressions in an XML schema. Validation of pattern facets with regular expressions in an XML schema may involve increased CPU usage and should be avoided in high availability scenarios.

  • Exceptions raised as a result of using the XmlSchemaSet class, such as the XmlSchemaException class may contain sensitive information that should not be exposed in untrusted scenarios. For example, the SourceUri property of an XmlSchemaException returns the URI path to the schema file that caused the exception. The SourceUri property should not be exposed in untrusted scenarios. Exceptions should be properly handled so that this sensitive information is not exposed in untrusted scenarios.

The example below uses the XmlReaderSettings object and the System.Xml.XmlReader.Create method to associate a schema with an XML document. The schema is added to the Schemas property of the XmlReaderSettings object. The value of the Schemas property is an XmlSchemaSet object. The schema is used to validate that the XML document conforms to the schema content model. Schema validation errors and warnings are handled by the ValidationEventHandler defined in the XmlReaderSettings object.

Imports System
Imports System.Xml
Imports System.Xml.Schema

Class XmlSchemaSetExample

    Shared Sub Main()

        Dim booksSettings As XmlReaderSettings = New XmlReaderSettings()
        booksSettings.Schemas.Add("", "contosoBooks.xsd")
        booksSettings.ValidationType = ValidationType.Schema
        AddHandler booksSettings.ValidationEventHandler, New ValidationEventHandler(AddressOf booksSettingsValidationEventHandler)

        Dim books As XmlReader = XmlReader.Create("contosoBooks.xml", booksSettings)

        While books.Read()

        End While

    End Sub

    Shared Sub booksSettingsValidationEventHandler(ByVal sender As Object, ByVal e As ValidationEventArgs)

        If e.Severity = XmlSeverityType.Warning Then
            Console.Write("WARNING: ")

        ElseIf e.Severity = XmlSeverityType.Error Then
            Console.Write("ERROR: ")
        End If

    End Sub

End Class

The example uses the books.xml file as input.

<bookstore xmlns="">
  <book genre="autobiography" publicationdate="1981" ISBN="1-861003-11-0">
    <title>The Autobiography of Benjamin Franklin</title>
  <book genre="novel" publicationdate="1967" ISBN="0-201-63361-2">
    <title>The Confidence Man</title>
  <book genre="philosophy" publicationdate="1991" ISBN="1-861001-57-6">
    <title>The Gorgias</title>

The example uses the books.xsd file as an input.

<?xml version="1.0" encoding="utf-8"?>
<xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="" xmlns:xs="">
    <xs:element name="bookstore">
                <xs:element maxOccurs="unbounded" name="book">
                            <xs:element name="title" type="xs:string" />
                            <xs:element name="author">
                                        <xs:element minOccurs="0" name="name" type="xs:string" />
                                        <xs:element minOccurs="0" name="first-name" type="xs:string" />
                                        <xs:element minOccurs="0" name="last-name" type="xs:string" />
                            <xs:element name="price" type="xs:decimal" />
                        <xs:attribute name="genre" type="xs:string" use="required" />
                        <xs:attribute name="publicationdate" type="xs:unsignedShort" use="required" />
                        <xs:attribute name="ISBN" type="xs:string" use="required" />


Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0

.NET Compact Framework

Supported in: 2.0