web.config under appsettings where should i mention the msde instance name

I have the following code under appsettings of web.config file:
How can i use my msde instance name(pcsnet) and database name: pcsdata
<appSettings>
<add key="Qmain" value="data source=ServerName;initial catalog=Database;persist security info=False;user id=username;password=password;" />
</appSettings>
Thank you very much for the info.

The server value should be serverName\instanceName. For example:
<appSettings>
<add key="Qmain" value="data source=ServerName\pcsnet;initial catalog=Database;persist security info=False;user id=username;password=password;" />
</appSettings>