<connectionStrings>
<add name="connection" connectionString="Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\MyDatas.mdf;Integrated Security=True;User Instance=True"/>
</connectionStrings>
string connectionString = ConfigurationManager.ConnectionStrings["connection"].ConnectionString;
<appSettings>
<add key="strcon" value="data source=2011-20111005ND;user id=sa;pwd=sa;database=DB_SSSL" />
</appSettings>
string connectionString = System.Configuration.ConfigurationManager.AppSettings["strcon"];