connectionstring by using web.config

< asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString=' < % $ ConnectionStrings:Main.ConnectionString % > '
SelectCommand="Select CategoryID, Title, UpperCategoryID From Category" / >

web.config:
< connectionStrings >
< add name="Main.ConnectionString" providerName="System.Data.SqlClient" connectionString="data source=pisipisi\sql2008; initial catalog=yapimatik; Trusted_Connection=yes" / >
< / connectionStrings>