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and one in-memory object class which functionsas an interface between BCS and its backend datasource:
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Those two are linked by object's type Name:
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reference: http://www.screencast.com/users/jthake/folders/SharePointDevWiki.com%20Screencast/media/10d81c1f-2bbf-417f-a307-1e88933b2864
http://weblogs.asp.net/scottgu/archive/2007/05/19/using-linq-to-sql-part-1.aspx
http://blogs.msdn.com/steve_fox/archive/2009/12/26/sharepoint-2010-development-using-bcs.aspx