public class Category {
  ...
  public bool Delete() { 
      if (this.Id > DefaultValues.GetCategoryIdMinValue()) {
        DataAccess DALLayer = DataAccessHelper.GetDataAccess();
        return DALLayer.DeleteCategory(this.Id);
      }
      else
        return false;
   }
  ...
}
//---------------------
public class DataAccessHelper { // Factory Pattern
    public static DataAccess GetDataAccess() {
       ...
       DataAccess dc = (DataAccess)Activator.CreateInstance(dataAccessType);
       return (dc); // кстати, почему здесь не Singleton?
    }
}
//---------------------
 public abstract class DataAccess {
...
    public abstract bool DeleteCategory(int categoryId);
...
}
//---------------------
public class SQLDataAccess : DataAccess { // Facade pattern
   ...
   private const string SP_CATEGORY_DELETE = "aspnet_starterkits_DeleteCategory";
   ...
   public override bool DeleteCategory(int categoryId) {
      if (categoryId <= DefaultValues.GetCategoryIdMinValue())
        throw (new ArgumentOutOfRangeException("categoryId"));

      SqlCommand sqlCmd = new SqlCommand();

      AddParamToSQLCmd(sqlCmd, "@ReturnValue", SqlDbType.Int,  0 , ParameterDirection.ReturnValue, null);
      AddParamToSQLCmd(sqlCmd, "@CategoryIdToDelete", SqlDbType.Int,  0 , ParameterDirection.Input, categoryId);

      SetCommandType(sqlCmd, CommandType.StoredProcedure, SP_CATEGORY_DELETE);
      ExecuteScalarCmd(sqlCmd);

      int returnValue = (int)sqlCmd.Parameters["@ReturnValue"].Value;
      return (returnValue ==  0  ? true : false); // wtf? :)))
  }
  ...
  private void ExecuteScalarCmd(SqlCommand sqlCmd) {
      if (ConnectionString == string.Empty)
        throw (new ArgumentOutOfRangeException("ConnectionString"));
      if (sqlCmd == null)
        throw (new ArgumentNullException("sqlCmd"));
      using (SqlConnection cn = new SqlConnection(this.ConnectionString)) {
        sqlCmd.Connection = cn;
        cn.Open();
        sqlCmd.ExecuteScalar();
      }
  }
  ...
}

class SQLDataAccess

  include SQLDataHelper

  include CategorySQLDataAccess
  include PersonSQLDataAccess

  attr_accessor :connection_string

  def initialize( conn_string)
    @connection_string = conn_string
  end
end

module SQLDataHelper
  def exec_scalar_cmd( sql_cmd )
    cn =SqlConnection.new(connection_string)
    sql_cmd.connection =  cn
    cn.open()
    sql_cmd.execute_scalar()
  end

  def add_param_to_sql_cmd(sql_cms, param_id, sql_type, param_size, param_direction, param_value)
    # [snipped]
  end

  def set_command_type(sql_cmd, reader, list)
    # [snipped]
  end
end

module CategorySQLDataAccess
   SP_CATEGORY_DELETE = "aspnet_starterkits_DeleteCategory"

   def delete_category(category_id)
     sql_cmd = SqlCommand.new
     add_param_to_sql_cmd(sql_cmd, "@ReturnValue", SqlDbType.Int,  0 , ParameterDirection.ReturnValue, nil)
     add_param_to_sql_cmd(sql_cmd, "@CategoryIdToDelete", SqlDbType.Int,  0 , ParameterDirection.Input, category_id)
     set_command_type(sql_cmd, CommandType.StoredProcedure, SP_CATEGORY_DELETE)
     execute_scalar_cmd(sql_cmd)
     return_value = sql_cmd.parameters["@ReturnValue"].value
     return (return_value ==  0 )
   end
end