The Entity Framework (EF) is an object persistence layer that includes an object/relational mapping (O/RM) tool to substitutes an object graph diagram for the traditional relational database schema. The duties of a persistence layer are to instantiate in memory a desired set of object instances together with a representation of their associations and save in-memory changes to objects and their property value to rows and columns of relational tables. What distinguishes EF from the 40-plus commercial and open-source O/RM tools for .NET is an intermediate mapping from the relational data model to the entity-relationship (E-R) data model proposed by Dr. Peter Chen in 1976 and called the Entity Data Model (EDM) by EF. Three XML files, a storage schema (
ssdl), mapping layer (
.msl), and conceptual schema (
.csdl) together with EF runtime code perform the object-to-relational mapping. The storage schema has a 1:1 relationship with the tables, keys, and relationships of the underlying database, called the persistence store. The conceptual schema represents the transformation by the mapping layer of the storage schema to a set of
EntitySet collections, and
AssociationSet collections with Common Language Runtime (CLR) data types. Thus ...