好久没写AE的东西了，好多东西都忘记了，这里记录一下直连Oracle，注意instance的拼接。

/// <summary>
        /// 连接Oracle数据库SDE
        /// </summary>
        /// <param name="sAddress">连接IP</param>
        /// <param name="sInstance">数据库实例名orcl</param>
        /// <param name="sUser">用户名</param>
        /// <param name="sPassword">密码</param>
        /// <returns></returns>
        public IWorkspace Con2OracleSDE(string sAddress, string sInstance, string sUser, string sPassword)
        {
            IWorkspaceFactory pSdeWksFactory = new SdeWorkspaceFactory();
            IWorkspace pWorkspace = null;
            try
            {
                IPropertySet propSet = new PropertySetClass();
                propSet.SetProperty("server", sAddress);
                //propSet.SetProperty("instance", "sde:oracle11g:" + sAddress + @"/" + sDBName);
                //propSet.SetProperty("instance", "sde:oracle11g:" + sDBName);
                propSet.SetProperty("instance", "sde:oracle11g$//" + sAddress + "/" + sInstance);               
                propSet.SetProperty("user", sUser);
                propSet.SetProperty("password", sPassword);
                propSet.SetProperty("version", "SDE.DEFAULT");

                pWorkspace = pSdeWksFactory.Open(propSet, 0);
                return pWorkspace;
            }
            catch (Exception ex)
            {
                return null;
            }
        }

另外也可以通过ArcCatalog中配置的数据库连接（.sde文件）进行数据库连接。