The comparison document mentions EF 4.0 to illustrate the fact that the latest features of EF are compared to the ones provided by OpenAccess. EF does support .NET 3.5 and so does OpenAccess.
The validation framework is a powerful feature that lets you locate inconsistencies in your OpenAccess metamodel. The moment you save your changes to the model any errors or warnings will appear immediately to notify you and remind you that the model needs to be brought into a consistent state so that you can work smoothly at runtime. The OpenAccess model errors and warnings appear respectively in the error and warning list panes of Visual Studio. Your project will be able to be built even with the errors present in the error list pane. This is because of the fact that the validation rules are there to help you locate possible runtime problems at an early stage. What is more, you can simply double-click one such error and a validation dialog will appear to assist you with the fixing of the issues spotted by the validation framework. Most of the validation rules have resolution actions (manual or automatic) which you can apply to immediately resolve the inconsistencies in your metamodel. Simply put, you can usually choose between several alternatives for managing the validation error detail. Such inconsistencies include missing primary keys, wrong concurrency mechanism set-up, missing identifiers, etc. More information on the Resolve Errors Dialog can be found here. A brief introduction on how to validate your model is available here.
We would like to hear your comments on the feature. If you need further information, do get back to us.
the Telerik team