<?xml version="1.0" standalone="yes"?>
<xs:schema id="NewDataSet" xmlns="" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
  <xs:complexType name="typeB">
    <xs:sequence>
      <xs:element name="A1" type="typeA" minOccurs="0" maxOccurs="unbounded" />
      <xs:element name="C" type="xs:string" />
    </xs:sequence>
  </xs:complexType>
  <xs:complexType name="typeA">
    <xs:attribute name="att1" type="xs:string" />
  </xs:complexType>
  <xs:element name="B" type="typeB" />
  <xs:element name="NewDataSet" msdata:IsDataSet="true" msdata:UseCurrentLocale="true">
    <xs:complexType>
      <xs:choice minOccurs="0" maxOccurs="unbounded">
        <xs:element ref="B" />
      </xs:choice>
    </xs:complexType>
  </xs:element>
</xs:schema>

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


namespace Test
{

  class Program
  {
    static void Main(string[] args)
    {

      DataSet ds = new DataSet();

      using (XmlReader reader = XmlReader.Create(@"schema.xsd"))
      {
        ds.ReadXmlSchema(reader);
      }

      ds.Tables["B"].Rows.Add(new object[] { "element C",  1  });
      ds.Tables["A1"].Rows.Add("attribute 1",  1 );

      XmlDataDocument doc = new XmlDataDocument(ds);
      using (XmlReader reader = XmlReader.Create(@"schema.xsd"))
      {
        XmlSchema schema = XmlSchema.Read(reader, null);
        doc.Schemas.Add(schema);
      }

      ds.WriteXml(@"out.xml");
      ds.WriteXmlSchema(@"out.xsd");

      try
      {
        doc.Validate(null);
      }
      catch (Exception e)
      {
        Console.Write(e);

        Console.ReadKey();
      }

    }
  }
}