Very often we have to manage objects and their changes over time. Usually we implement this by adding a Range to the data. Martin Fowler has a name for this pattern: Effectivity and i have an implementation for the following interface

public interface IEffectivity<T> : IComparable<ieffectivity<T>>
{
	T Element { get; }
	IRange<dateTime> ValidityPeriod { get; }
	bool IsEffectiveOn(DateTime validityDate);
}

Feel free to download IEffectivity.txt, Effectivity.txt and EffectivityTester.txt.