public static String GetFileExtName(IServiceContext service, String FileName, String url, string repositoryName)
{
      String extname = "unknow";
      String FileExtName = UpperToLower(System.IO.Path.GetExtension(FileName));
      if (FileExtName.LastIndexOf(".") >= 0)
      {
            FileExtName = FileExtName.Substring(1, FileExtName.Length-1);
      }
      try
      {
            IQueryService QueryService = NewQueryService(service, url);
            PassthroughQuery query = new PassthroughQuery();
            query.QueryString = "select dos_extension,name,description from dm_format where dos_extension='" + FileExtName + "'";
            query.AddRepository(repositoryName);
            QueryExecution queryEx = new QueryExecution();
            queryEx.CacheStrategyType = CacheStrategyType.DEFAULT_CACHE_STRATEGY;
            QueryResult queryResult = QueryService.Execute(query, queryEx, null);
            DataPackage resultDp = queryResult.DataPackage;
            List<Emc.Documentum.FS.DataModel.Core.DataObject> dataObjects = resultDp.DataObjects;
            if (dataObjects.Count > 0)
            {
                  Emc.Documentum.FS.DataModel.Core.DataObject dataObject = dataObjects[0];
                  extname= dataObject.Properties.Get("name").GetValueAsString();
            }
      }
      catch (Exception ex)
      {
      }
      finally
      {
      }
      return extname;
}

public static IQueryService NewQueryService(IServiceContext serviceContext, string url)
{
      IQueryService queryservice = ServiceFactory.Instance.GetRemoteService<IQueryService>(serviceContext,
      "core", url);
      return queryservice;
}