Using LINQ to SQL in your phone app requires referencing the assembly
System.Data.Linq, which is included in the Windows Phone Framework Class Library (FCL).
There are two commonly used approaches to the creation of an application’s data model: code-first and database-first. Code-first entails writing your classes first, and then using those classes to generate the database. Conversely, database-first entails creating your database schema and then using a tool to generate an object model for interacting with the database. The database-first approach is discussed later in the chapter. For now, though, we concentrate on the code-first approach.