1. A method of explicitly declaring expected relationships between expected entities and a reference entity in a model, said reference entity have a reference data type definition associated therewith, said method comprising: creating an expected targets tag in a markup language schema type declaration; defining one or more elements describing one or more expected entities in the model; identifying a predefined entity relationship; associating the expected targets tag with the defined elements and the identified, predefined entity relationship; and locating the expected targets tag and associated elements and predefined entity relationship in the reference data type definition of the reference entity to declare a relationship between the expected entities and the reference entity.