Commit c866f5e

@@ -38,6 +38,14 @@ The range of an attribute is bounded or not:
 * Infinite Domain Attribute: Range of this attribute type is a countably
   infinite set of attribute values.
 
+## Weaknesses
+
+It is often claimed that attributes can express relationships, and indeed this
+is trivial for direct relationships. However, the use of indirect relations,
+also called multilevel or composite relations, is fundamental to ReBAC. It is
+hard to see how ABAC can express long chains of relationships. It has been
+suggested that ReBAC emerged to overcome this shortcoming of attributes.
+
 ## See Also
 
 * [Classifying and Comparing Attribute-Based and Relationship-Based Access Control][5]

@@ -20,8 +20,6 @@ authorized to perform an action against a resource.
   end
 ```
 
-* [Zanzibar](./ZANZIBAR.md)
-
 ## Policy Language
 
 A policy language facilitates:
@@ -29,6 +27,8 @@ A policy language facilitates:
 1. the specification of composite policies, which in turn forms the basis of trust delegation.
 1. **the static analysis of policies and system configuration.**
 
+
+
 ## Security Context/Scope
 
 1. Single resource
@@ -59,3 +59,8 @@ end
 ```
 
 [Social Network Graph](./sns.dot.png)
+
+## See Also
+
+* [Zanzibar](./ZANZIBAR.md)
+* [Dafny](https://dafny.org)