I mentioned a little while ago that I was going to cover the DataServiceProviderMethods class. It's a mysterious class, where all methods simply throw a NotImplementedException. You can't subclass to implement the members, you can't provide a hook to provide an implementation. What is this thing doing in your library?
Well, I will simply defer to Vitek's excellent post on property access expressions, in which he explains the rationale for this class, what does WCF Data Services use it for, and what is it that custom providers may choose to do with it.