研究出来了，不过可能不规范 呵呵

用来生成xml的（不知道为什么 flash必须这样访问。。）         比老师做的有效率呵呵

SqlConnection myconn = new SqlConnection("Data Source=.;Initial Catalog=libdb;Integrated Security=True");
        SqlDataAdapter myda = new SqlDataAdapter("select * from dball",myconn);
        DataSet myds=new DataSet();
        myconn.Open();
        myda.Fill(myds);
        DataTable mytb = myds.Tables[0];
        DataRow[] myrows = mytb.Select("dbclass='maindb'");
       
        string output="";
        output+="<?xml version='1.0' encoding='gbk'?>";

        output += "<数据库>";
        output+="<文献期刊>";
        foreach (DataRow a in myrows)
        {
            output += "<db name='" + a.ItemArray[0] + "' url='" + a.ItemArray[1] + "'><![CDATA[" + a.ItemArray[2] + "]]></db>";
        }
            output+="</文献期刊>";
        output+="<自建数据库>";