This post is published on Jeff Handley's blog but is actually written by Kyle McClellan. Kyle explains how to write a filter or parameter for DomainDataSource.
Now that the ControlParameter has been properly disposed of, you might have noticed that Parameter has changed substantially. Before, a Parameter was used for filtering, grouping, sorting, and querying. Now it is only used in the last case. If you had previously defined your own parameter types, you might be wondering how to leverage them in the RIA Services RC release.