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 in the model; defining one or more elements describing one or more expected entities according to the created expected targets tag in the model; identifying a predefined entity relationship, said described one or more expected entities being expected entities based on the predefined entity relationship and are not required entities based on the predefined entity relationship; associating the expected targets tag with the defined one or more elements and the identified, predefined entity relationship; locating the expected entities in the reference data type definition having the expected targets tag and associated elements and predefined entity relationship; and declaring a relationship between the located expected entities and the reference entity in response to the locating.