[Code Snippet] : Connect to Sql Server from ArcObject

 using System;

using ESRI.ArcGIS.DataSourcesFile;

using ESRI.ArcGIS.esriSystem;

using ESRI.ArcGIS.Geodatabase;

namespace MyNamespace

{

  class MyProgram

  {

    private static LicenseInitializer _licenseInitializer = new LicenseInitializer();

    [STAThread()]

    static void Main(string[] args)

    {

      _licenseInitializer.InitializeApplication(new esriLicenseProductCode[] { esriLicenseProductCode.esriLicenseProductCodeEngineGeoDB },

                                                   new esriLicenseExtensionCode[] { });

      Type factoryType = Type.GetTypeFromProgID("esriDataSourcesGDB.SqlWorkspaceFactory");

      IPropertySet propertySet = new PropertySetClass();

      propertySet.SetProperty("SERVER", "servername");

      propertySet.SetProperty("INSTANCE", "sde:sqlserver:servername");

      propertySet.SetProperty("AUTHENTICATION_MODE", "DBMS");

    // propertySet.SetProperty("AUTHENTICATION_MODE", "OSA");

      propertySet.SetProperty("DATABASE", "test1");

      propertySet.SetProperty("USER", "username");

      propertySet.SetProperty("PASSWORD", "password");

      propertySet.SetProperty("VERSION", "sde.DEFAULT");

      IWorkspaceFactory workspaceFactory = new SDCWorkspaceFactory();

      IWorkspace workspace = workspaceFactory.Open(propertySet, 0);

    }

  }

}