Background In dotnet-architecture/eShopOnWeb I noticed the interesting usage of Specification classes. When I did some digging, I found that these are implemented through ardalis/Specification For those who are more familiar with the Java world we have Data Specifications. If you read Implementing Domain Driven design in the bibliography you find a reference to Martin Fowlers paper. Sample based on Wikipedia So if we look at Wikipedia we can infer the following code: public class OverDueSpecification :[...]