Update coreTypes.md

Add link to nav prop article

graph/articles/coreTypes.md

@@ -17,10 +17,7 @@ The following types are identified as core types, and will require strong justif
 ## Alternatives to Adding Structural Properties
 
 Instead of adding a structural property to the existing type (`user`, `group` or `device`), create a new type that models the information captured in the proposed structural property(s).
-Then, do one of the following:
-- Add a navigation property on the existing type to the new type, containing the new type.
-- Contain the new type in an entity set elsewhere, and add a navigation property to the new type on the existing type.
-- Contain the new type in an entity set elsewhere, and add a navigation property to the existing type on the new type.
+Then, model the relationship between the existing core type and the new type by adding a navigation property. For information on modeling with navigation properties, see [Navigation Property](../patterns/navigation-property.md).
 
 ## Example:
 
@@ -39,7 +36,7 @@ Don't add new properties to core types such as `user`.
 
 ### Do:
 
-Do one of the following:
+Model the information by creating a new type and model the relationship to the existing core type with a navigation property. To determine which option is most appropriate, see [Navigation Property](../patterns/navigation-property.md):
 
 #### Option 1: Add a navigation property on the existing type to the new type, containing the new type.