What is the reference for ´System.Data.Entity.Infrastructure´?

Using Entity Framework Power Tools Beta 2 extension, it generates model classes with the following imports:

using System.Data.Entity.Infrastructure;

What reference do I need to include into my project using Visual Studio 2010?

Currently, I have the following References:

• log4net
• System.configuration
• System.Core
• System.Data
• System.Data.Entity
• System.Web
• System.Web.Mvc
• System.XML

And in the Add Reference dialog I have the following: