How to convert XML to JSON using C#/LINQ?

using System;
using System.Linq;
using System.Web.Script.Serialization;
using System.Xml.Linq;

class Program
{
    static void Main()
    {
        var xml = 
        @"<Columns>
          <Column Name=""key1"" DataType=""Boolean"">True</Column>
          <Column Name=""key2"" DataType=""String"">Hello World</Column>
          <Column Name=""key3"" DataType=""Integer"">999</Column>
        </Columns>";
        var dic = XDocument
            .Parse(xml)
            .Descendants("Column")
            .ToDictionary(
                c => c.Attribute("Name").Value, 
                c => c.Value
            );
        var json = new JavaScriptSerializer().Serialize(dic);
        Console.WriteLine(json);
    }
}

produces:

{"key1":"True","key2":"Hello World","key3":"999"}

Obviously this treats all the values as strings. If you want to keep the underlying type semantics you could do the following:

using System;
using System.Linq;
using System.Web.Script.Serialization;
using System.Xml.Linq;

class Program
{
    static void Main()
    {
        var xml = 
        @"<Columns>
          <Column Name=""key1"" DataType=""System.Boolean"">True</Column>
          <Column Name=""key2"" DataType=""System.String"">Hello World</Column>
          <Column Name=""key3"" DataType=""System.Int32"">999</Column>
        </Columns>";
        var dic = XDocument
            .Parse(xml)
            .Descendants("Column")
            .ToDictionary(
                c => c.Attribute("Name").Value, 
                c => Convert.ChangeType(
                    c.Value,
                    typeof(string).Assembly.GetType(c.Attribute("DataType").Value, true)
                )
            );
        var json = new JavaScriptSerializer().Serialize(dic);
        Console.WriteLine(json);
    }
}

produces:

{"key1":true,"key2":"Hello World","key3":999}

And if you cannot modify the underlying XML structure you will need a custom function that will convert between your custom types and the underlying .NET type:

using System;
using System.Linq;
using System.Web.Script.Serialization;
using System.Xml.Linq;

class Program
{
    static void Main()
    {
        var xml = 
        @"<Columns>
          <Column Name=""key1"" DataType=""Boolean"">True</Column>
          <Column Name=""key2"" DataType=""String"">Hello World</Column>
          <Column Name=""key3"" DataType=""Integer"">999</Column>
        </Columns>";
        var dic = XDocument
            .Parse(xml)
            .Descendants("Column")
            .ToDictionary(
                c => c.Attribute("Name").Value, 
                c => Convert.ChangeType(
                    c.Value, 
                    GetType(c.Attribute("DataType").Value)
                )
            );
        var json = new JavaScriptSerializer().Serialize(dic);
        Console.WriteLine(json);
    }

    private static Type GetType(string type)
    {
        switch (type)
        {
            case "Integer":
                return typeof(int);
            case "String":
                return typeof(string);
            case "Boolean":
                return typeof(bool);
            // TODO: add any other types that you want to support
            default:
                throw new NotSupportedException(
                    string.Format("The type {0} is not supported", type)
                );
        }
    }
}