I've written a four part series on the Specification Design pattern. The four articles are available now on codeproject.com. The articles take you from an introduction to the pattern to a simple VB.Net implementation and finaly to a reusable Specification class that uses inheritence, generics and Operator Overloading.

• Part 1 - An Introduction to the Specification Design Pattern
• Part 2 - A simple implementation of the pattern in VB.NET
• Part 3 - A Generic Specification with Operator Overloading
• Part 4 - Using the Generic Specification

My article on modelling attributes using value objects is available on eggheadcafe. It'll take you though the process of modelling a Temperature attribute, starting with a naive implementation and working towards a fully fledged value object.

See Here