A: 

Understand something: You, the programmer, are the only one who knows what validation is appropriate for each and every property in your program. As such, you are the one who gets to write the validation code.

Can you define a Length_Validated_String class, that validates the length of the string, and then let your various other presentation models use that class, and the validation for it, instead of reinventing the wheel each time?

John R. Strohm
I think I might not have explained it correctly. However Darin Dimitrov's suggestion is the one I was looking for. Thanks.
Mano
A: 

You could take a look at FluentValidation. It is a great framework that allows you to separate the validation logic of your model from the model itself, provides easy way to unit test the validation logic and could be used in any type of application and of course seamlessly integrates with ASP.NET MVC.

Darin Dimitrov
Thanks Darin this is exactly what I was looking for. I will try that out.
Mano