Three Tier Structure (from code behind to data access)

Question

Hello everyone, I created an xml file from a gridview (thanks to Rakesh article). My application is done using a 3 tier structure. How will I transfer my code behind to data access and call only the xml from my code behind? Please see code below.

 

StringBuilder sbSubjects = new StringBuilder();
                sbSubjects.AppendLine("<?xml version=\"1.0\" ?>");

                foreach (GridViewRow row in GridView1.Rows)
                {
                    Label SubjectID = (Label)row.FindControl("lblSubjectId");
                    string lblEnrollmentId = lblEnrollmentID.Text.Trim();

                    if (SubjectID == null || lblEnrollmentId == null)
                    {
                        return;
                    }

                    if (string.IsNullOrEmpty(SubjectID.Text.Trim()) || string.IsNullOrEmpty(lblEnrollmentId))
                    {
                        return;
                    }
                    else
                    {
                        sbSubjects.AppendLine("<tblEnrolledSubjects>");
                        sbSubjects.AppendLine(" <subjects>");
                        sbSubjects.AppendLine("  <SubjectId>" + SubjectID.Text.Trim() + "</SubjectId>");
                        sbSubjects.AppendLine("  <EnrollmentID>" + lblEnrollmentId + "</EnrollmentID>");
                        sbSubjects.AppendLine(" </subjects>");
                        sbSubjects.AppendLine("</tblEnrolledSubjects>");
                    }

                }
                SqlCommand cmdSubjects = new SqlCommand("[dbo].[spInsert_XML_BulkEnrollmentSubjects]", con, transaction);
                cmdSubjects.CommandType = CommandType.StoredProcedure;
                cmdSubjects.Parameters.AddWithValue("@SubjectsData", sbSubjects.ToString());