In this appendix, we described what ADO.NET Entity Framework is and how to use it to realize a conceptual abstraction from the physical data layer. You have seen how to define EDM schemas using the metadata files (CSDL, SSDL, and MSL) and the code automatically generated by Visual Studio Orcas in parsing these metadata files. The entities generated from the metadata can be queried with an SQL-like query language, and they can also be queried using LINQ to Entities. Finally, you have seen how to change and persist entities-including how to handle concurrency and transactions-using the ObjectContext infrastructure.