Hi AlirezaHaghshenas,
The .NET Framework already has an assembly for data annotations (System.ComponentModel.DataAnnotations.dll). This is the assembly for "standard .NET data annotations" and is already promoted as such. For .NET 4.5 we moved the data annotations from EntityFramework.dll into this assembly, so in a sense we have already done what you are suggesting. The caveat is that you need to be using .NET 4.5 for this to be useful because System.ComponentModel.DataAnnotations.dll is part of the .NET Framework, which is something we on the EF team can't change at this time.
It's also worth noting that everything you can do with the data annotations from EntityFramework.dll can also be done with the Code First fluent API. This means that you can create the same Code First model without having any reference to EntityFramework.dll from the entity classes. Of course, there may be other reasons why you want to use the data annotations, but in terms of Entity Framework functionality they are not required.
Thanks,
Arthur