สอบถามหน่อยครับโปรเจคเกี่ยวกับC#จะใช้ฐานข้อมูลตัวไหนดี

        public bool WriteInfo()
        {
            XmlDocument info = new XmlDocument();

            if (File.Exists(string.Format("{0}\\xml\\info.xml", System.Windows.Forms.Application.StartupPath)))
            {
                File.Delete(string.Format("{0}\\xml\\info.xml", System.Windows.Forms.Application.StartupPath));
            }

            XmlDeclaration xmldecl = info.CreateXmlDeclaration("1.0", "UTF-8", null);
            info.AppendChild(xmldecl);

            XmlElement dataroot = info.CreateElement("dataroot");
            dataroot.SetAttribute("xmlns:od", "urn:schemas-microsoft-com:officedata");
            dataroot.SetAttribute("generated", DateTime.Now.ToString("yyyy-MM-ddTHH:mm:ss"));
            info.AppendChild(dataroot);

            XmlElement newElem = info.CreateElement("FileInfo");
            info.DocumentElement.AppendChild(newElem);

            XmlElement FileName = info.CreateElement("FileName");
            FileName.InnerText = fileName;
            newElem.AppendChild(FileName);

            XmlElement ReadExcel = info.CreateElement("ReadExcel");
            ReadExcel.InnerText = "True";
            newElem.AppendChild(ReadExcel);

            XmlElement CheckData = info.CreateElement("CheckData");
            CheckData.InnerText = "False";
            newElem.AppendChild(CheckData);

            XmlElement CheckLocation = info.CreateElement("CheckLocation");
            CheckLocation.InnerText = "False";
            newElem.AppendChild(CheckLocation);

            XmlElement CheckProduct = info.CreateElement("CheckProduct");
            CheckProduct.InnerText = "False";
            newElem.AppendChild(CheckProduct);

            XmlElement CheckSection = info.CreateElement("CheckSection");
            CheckSection.InnerText = "False";
            newElem.AppendChild(CheckSection);

            XmlElement CheckName = info.CreateElement("CheckName");
            CheckName.InnerText = "False";
            newElem.AppendChild(CheckName);

            info.Save(string.Format("{0}\\xml\\info.xml", System.Windows.Forms.Application.StartupPath));

            return true;
        }

        public bool WriteCircuit(int StartIndex)
        {
            byte[] endtag = System.Text.Encoding.UTF8.GetBytes("</dataroot>");
            XmlTextWriter writer;

            bool fileExist = File.Exists(string.Format("{0}\\xml\\circuit.xml", System.Windows.Forms.Application.StartupPath));

            if (fileExist)
            {
                FileStream fileStream = File.OpenWrite(string.Format("{0}\\xml\\circuit.xml", System.Windows.Forms.Application.StartupPath));
                fileStream.Seek(-endtag.Length, SeekOrigin.End);

                writer = new XmlTextWriter(fileStream, Encoding.UTF8);
            }
            else
            {
                writer = new System.Xml.XmlTextWriter(string.Format("{0}\\xml\\circuit.xml", System.Windows.Forms.Application.StartupPath), System.Text.Encoding.UTF8);
                writer.WriteStartDocument();
                writer.WriteStartElement("dataroot");
                writer.WriteAttributeString("xmlns", "od", null, "urn:schemas-microsoft-com:officedata");
                writer.WriteAttributeString("generated", DateTime.Now.ToString("yyyy-MM-ddTHH:mm:ss"));
            }

            writer.Indentation = 1;
            writer.IndentChar = Convert.ToChar(" ");
            writer.Formatting = Formatting.Indented;

            for (int i = StartIndex; i < StartIndex + 1000; i++)
            {
                if (i < circuitData.Rows.Count)
                {
                    System.Data.DataRow newCircuit = circuitData.Rows[i];

                    writer.WriteStartElement("Circuit");

                    writer.WriteElementString("InvoiceDate", invoiceDate.ToShortDateString());
                    writer.WriteElementString("CircuitID", newCircuit["CircuitID"].ToString());
                    writer.WriteElementString("ProductName", newCircuit["ProductName"].ToString());
                    writer.WriteElementString("ProductCode", newCircuit["ProductCode"].ToString());
                    writer.WriteElementString("CustomerName", newCircuit["CustomerName"].ToString().Trim());
                    writer.WriteElementString("CustomerCode", newCircuit["CustomerCode"].ToString());
                    writer.WriteElementString("CustomerType", newCircuit["CustomerType"].ToString());
                    writer.WriteElementString("InstallDate", (newCircuit["InstallDate"] != DBNull.Value) ? Convert.ToDateTime(newCircuit["InstallDate"]).ToShortDateString() : string.Empty);
                    writer.WriteElementString("Origin", newCircuit["Origin"].ToString());
                    writer.WriteElementString("Destination", newCircuit["Destination"].ToString());
                    writer.WriteElementString("Amount", newCircuit["Amount"].ToString());
                    writer.WriteElementString("Discount", newCircuit["Discount"].ToString());
                    writer.WriteElementString("Balance", newCircuit["Balance"].ToString());
                    writer.WriteElementString("Vat", newCircuit["Vat"].ToString());

                    writer.WriteEndElement();
                }
            }

            if (!fileExist)
            {
                writer.WriteEndElement();
                writer.WriteEndDocument();
            }
            else
            {
                writer.Flush();
                writer.BaseStream.Write(endtag, 0, endtag.Length);
            }

            if (writer != null)
            {
                writer.Flush();
            }

            if (writer.WriteState != WriteState.Closed)
            {
                writer.Close();
            }

            return true;
        }

Uri infoPath = new Uri(string.Format("{0}\\xml\\info.xml", System.Windows.Forms.Application.StartupPath));

XElement xInfo = (from x in XElement.Load(infoPath.LocalPath).Elements("FileInfo")
          select x).First();

        private void UpdateInfo()
        {
            Uri infoPath = new Uri(string.Format("{0}\\xml\\info.xml", System.Windows.Forms.Application.StartupPath));

            try
            {
                XElement xInfo = XElement.Load(infoPath.LocalPath);

                var info = from xi in xInfo.Elements("FileInfo")
                           select xi;

                foreach (XElement xe in info)
                {
                    xe.Element("CheckData").ReplaceWith(new XElement("CheckData", "True"));
                    xe.Element("CheckLocation").ReplaceWith(new XElement("CheckLocation", "True"));
                    xe.Element("CheckProduct").ReplaceWith(new XElement("CheckProduct", "False"));
                    xe.Element("CheckSection").ReplaceWith(new XElement("CheckSection", "False"));
                    xe.Element("CheckName").ReplaceWith(new XElement("CheckName", "False"));
                }

                xInfo.Save(infoPath.LocalPath);
            }
            catch { }
        }