// URL format of the POST query to DataService to update data.
http(s)://[Bpm'online application address]/[Configuration number]/dataservice/[Data fromat]/reply/UpdateQuery
// URL example of the POST query to DataService to update data.
http(s)://example.bpmonline.com/0/dataservice/json/reply/UpdateQuery

{
    "RootSchemaName":"[Root schema]",
    "OperationType":[Type of operation with record],
    "IsForceUpdate":[Force update],
   "ColumnValues":{
        "Items":{
            "Name of the added column":{
                "ExpressionType":[Expression type],
                "Parameter":{
                    "DataValueType":[Data type],
                    "Value":"[Column value]"
                }
            }...
        }
    },
    "Filters":[Request filters]
}

using System;
using System.Text;
using System.IO;
using System.Net;
using System.Collections.Generic;
using Terrasoft.Nui.ServiceModel.DataContract;
using Terrasoft.Core.Entities;
using System.Web.Script.Serialization;
using Terrasoft.Common;

// Primary URL of bpm'online application. Must be repoaced with a custom one.
private const string baseUri = @"http://example.bpmonline.com";
// Request string to the Login methid of the AuthService.svc service.
private const string authServiceUri = baseUri + @"/ServiceModel/AuthService.svc/Login";
// Path string for the UpdateQuery.
private const string updateQueryUri = baseUri + @"/0/DataService/json/reply/UpdateQuery";
// Bpm'online authentication cookie.
private static CookieContainer AuthCookie = new CookieContainer();

// Instance of the request class.
 var updateQuery = new UpdateQuery()
 {
     // Root schema name.
     RootSchemaName = "Contact",
     // New column values.
     ColumnValues = new ColumnValues()
     {
         // Key-value collection.
         Items = new Dictionary<string, ColumnExpression>()
         {
             // [Email] column.
             {
                 // key.
                 "Email",
                 // Value — instance of object schema request class.
                 // Configuration of [Email] column.
                 new ColumnExpression()
                 {
                     // Type of expression of obkect schema query — parameter.
                     ExpressionType = EntitySchemaQueryExpressionType.Parameter,
                     // Query expression parameter.
                     Parameter = new Parameter()
                     {
                         // Parameter value.
                         Value = "j.smith@bpmonline.com",
                         // Parameter data type — string.
                         DataValueType = DataValueType.Text
                     }
                 }
             }
         }
     },
     // Query filters.
     Filters = new Filters()
     {
         // Filter type — group.
         FilterType = Terrasoft.Nui.ServiceModel.DataContract.FilterType.FilterGroup,
         // Filter collection.
         Items = new Dictionary<string, Filter>()
         {
              // Filter by name.
             {
                 // Key.
                 "FilterByName",
                 // Value.
                 new Filter
                 {
                     // Filter type — comparison filter.
                     FilterType = Terrasoft.Nui.ServiceModel.DataContract.FilterType.CompareFilter,
                     // Comparison type — starts with expression.
                     ComparisonType = FilterComparisonType.Equal,
                     // Expression to check.
                     LeftExpression = new BaseExpression()
                     {
                         // Expression type - schema column.
                         ExpressionType = EntitySchemaQueryExpressionType.SchemaColumn,
                         // Path to column.
                         ColumnPath = "Name"
                     },
                     // Filtering expression.
                     RightExpression = new BaseExpression()
                     {
                         // Expression type - parameter.
                         ExpressionType = EntitySchemaQueryExpressionType.Parameter,
                          // Expression parameter.
                         Parameter = new Parameter()
                         {
                             // Parameter data type - text.
                             DataValueType = DataValueType.Text,
                             // Parameter value.
                             Value = "John Smith"
                         }
                     }
                 }
             }
         }
     }
 };
 // Serialization of update query class instance in a JSON string.
 var json = new JavaScriptSerializer().Serialize(updateQuery);

// Converting a JSON object string to a byte array.
byte[] jsonArray = Encoding.UTF8.GetBytes(json);
// Creating an insrance of HTTP request.
var updateRequest = HttpWebRequest.Create(updateQueryUri) as HttpWebRequest;
// Defining a request method.
updateRequest.Method = "POST";
// Determining type of request content.
updateRequest.ContentType = "application/json";
// Adding authentication cookie received earlier to a request.
updateRequest.CookieContainer = AuthCookie;
// Set length for request content.
updateRequest.ContentLength = jsonArray.Length;
// Plase a JSON-object to request content.
using (var requestStream = updateRequest.GetRequestStream())
{
    requestStream.Write(jsonArray, 0, jsonArray.Length);
}
// Executing HTTP request and getting a response from server.
using (var response = (HttpWebResponse)updateRequest.GetResponse())
{
    // Displaying response in console.
    using (StreamReader reader = new StreamReader(response.GetResponseStream()))
    {
        Console.WriteLine(reader.ReadToEnd());
    }
}