If you are interested in the history of LINQ to SQL and how it works internally, go watch Charlie Calvert's video with Matt Warren and Luca Bolognese.
The first 30 minutes of this video are primarily about the internals. The last 10 minutes focus on the history of LINQ to SQL and how it relates to its "predecessors" Cω and ObjectSpaces. Matt and Luca also tell how Erik Meijer and Anders Hejlsberg got involved.
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