added order and relevance attributes to Relation class

git-svn-id: svn://svn.cy55.de/Zope3/src/cybertools/trunk@2138 fd906abe-77d9-0310-91a1-e0d9ade77398

relation/__init__.py

@@ -35,6 +35,9 @@ class Relation(Persistent):
 
     implements(IPredicate, IRelation)
 
+    order = 0
+    relevance = 1.0
+
     @classmethod
     def getPredicateName(cls):
         return '%s.%s' % (cls.__module__, cls.__name__)
@@ -47,10 +50,10 @@ class Relation(Persistent):
             if obj is not None and not IRelatable.providedBy(obj):
                 raise(ValueError, 'Objects to be used in relations '
                         'must provide the IRelatable interface.')
-    
+
 
 class DyadicRelation(Relation):
-    
+
     implements(IDyadicRelation)
 
     def __init__(self, first, second):
@@ -60,7 +63,7 @@ class DyadicRelation(Relation):
 
 
 class TriadicRelation(Relation):
-    
+
     implements(ITriadicRelation)
 
     def __init__(self, first, second, third):

relation/interfaces.py

@@ -32,6 +32,13 @@ class IRelation(Interface):
     """ Base interface for relations.
     """
 
+    order = Attribute('An integer that may be used for ordering relations. '
+                'The default should be 0, and there may be negative and '
+                'positive values.')
+    relevance = Attribute('A float greater than 0.0 and less or equal to '
+                '1.0 denoting the importance, relevance, or weight of a '
+                'relation. The default and standard value should be 1.0.')
+
     def getPredicateName():
         """ Return the predicate of this relation as a string that may be
             used for indexing.
@@ -41,7 +48,9 @@ class IRelation(Interface):
         """ Return True if this relation is valid.
 
             If the registry argument is provided the check should be done
-            with respect to this relation registry, e.g. to
+            with respect to this relation registry. The validate() method
+            may be used for implementing checks against ontologies or other
+            kinds of restrictions.
         """