http://msdn.microsoft.com/en-us/library/ff664356(v=pandp.50).aspx
http://gorodinski.com/blog/2012/05/19/validation-in-domain-driven-design-ddd/
http://lostechies.com/jimmybogard/2009/02/15/validation-in-a-ddd-world/
http://abdullin.com/journal/2009/1/29/ddd-and-rule-driven-ui-validation-in-net.html