3 files changed, 142 insertions, 0 deletions
diff --git a/src/server/model/__init__.py b/src/server/model/__init__.py
new file mode 100644
index 00000000..e69de29b
--- /dev/null
+++ b/src/server/model/__init__.py
diff --git a/src/server/model/graph.py b/src/server/model/graph.py
new file mode 100644
index 00000000..f197921d
--- /dev/null
+++ b/src/server/model/graph.py
@@ -0,0 +1,105 @@
+class Attr_Diff(dict):
+    """
+    Represents a change to note attributes, where nodes can represent
+    either logical nodes or logical links, and attributes can be added,
+    changed or removed
+    
+    Example:
+            attr_diff = {'__type_node' : {n_id: {'__attr_write': {'attr_0': 0,
+                                                                  'attr_1': 'a'},
+                                                '__attr_remove': ['attr_2'] }}
+                         '__type_link' : {l_id: ... }
+                        }
+    """
+    def __init__(self):
+        self['__type_node'] = {}
+        self['__type_link'] = {}
+
+    def init_node_attr_diff(self, n_id):
+        ret = {'__attr_write': {},
+               '__attr_remove': []}
+        self['__type_node'][n_id] = ret
+        return ret
+
+    @staticmethod
+    def from_json_dict(json_dict):
+        ret = Attr_Diff()
+        for obj_type in ret.keys():
+            obj_ad_set = json_dict.get(obj_type)
+            if None != obj_ad_set:
+                for o_id, ad in obj_ad_set.items():
+                    if None != ad.get('__attr_write'):
+                        for k, v in ad['__attr_write'].items():
+                            ret.add_node_attr_write(o_id, k, v)
+                    if None != ad.get('__attr_remove'):
+                        for k in ad['__attr_remove']:
+                            ret.add_node_attr_rm(o_id, k)
+        return ret
+
+    @property
+    def type__node(self):
+        return self['__type_node']
+
+    @property
+    def type__link(self):
+        return self['__type_link']
+
+    def add_node_attr_write(self, n_id, attr_name, attr_val):
+
+        assert 'id' != attr_name.lower(), 'Attr_Diff: attempt to write to \'id\' attribute'
+
+        n_attr_diff = self['__type_node'].get(n_id)
+        if None == n_attr_diff:
+            n_attr_diff = self.init_node_attr_diff(n_id)
+        n_attr_diff['__attr_write'][attr_name] = attr_val
+
+    def add_node_attr_rm(self, n_id, attr_name):
+        n_attr_diff = self['__type_node'].get(n_id)
+        if None == n_attr_diff:
+            n_attr_diff = self.init_node_attr_diff(n_id)
+        n_attr_diff['__attr_remove'].append(attr_name)
+
+    def add_link_attr_write(self, l_id, attr_name, attr_val):
+        assert False, 'unimplemented'
+
+    def add_link_attr_rm(self, l_id, attr_name):
+        assert False, 'unimplemented'
+
+class Topo_Diff(object):
+    """
+    Represents a change to the graph topology
+    """
+    def __init__(self, link_set_rm=[],
+                       node_set_rm=[],
+                       node_set_add=[],
+                       link_set_add=[]):
+
+        self.link_set_rm = link_set_rm
+        self.node_set_rm = node_set_rm
+        self.node_set_add = node_set_add
+        self.link_set_add = link_set_add
+
+    def __str__(self):
+        return __name__ + ': ' + ', '.join('%s: %s' % (k, v) for k, v in self.__dict__.items())
+
+    def check_validity(self, topo_diff_dict):
+        """
+        Topo_Diff may represent invalid operations, eg. adding a link while
+         removing it's end-point - this stub should check for that
+        """
+        pass
+
+    @staticmethod
+    def from_json_dict(json_dict):
+        """
+        construct from dict - no node/link constructor set must be provided
+        """
+        ret = Topo_Diff()
+
+        # merge keys - this allows constructor argument omission (link_set_rm,
+        # node_set_rm, etc.) such as when constructing from POST JSON data
+        for k, _ in ret.__dict__.items():
+            v = json_dict.get(k)
+            if None != v:
+                ret.__dict__[k] = v
+        return ret
diff --git a/src/server/model/model.py b/src/server/model/model.py
new file mode 100644
index 00000000..33cf9e6a
--- /dev/null
+++ b/src/server/model/model.py
@@ -0,0 +1,37 @@
+class Link():
+    """
+    documentation anchor - this class currently carries no implementation
+    and only acts as a documentation anchor
+    
+    link['__src'] - meta attribute for link source object
+    link['__dst'] - meta attribute for link destination object
+    """
+
+    def __init__(self, src=None, dst=None):
+        assert False, 'currently unused'
+
+    class Link_Ptr(dict):
+        """
+        link['__src_id'] - meta attribute for link source id
+        link['__dst_id'] - meta attribute for link destination id
+        """
+        def __init__(self, src_id=None, dst_id=None):
+            assert None != src_id or None != dst_id
+
+            self['__src_id'] = src_id
+            self['__dst_id'] = dst_id
+
+        @property
+        def src_id(self):
+            return self['__src_id']
+
+        @property
+        def dst_id(self):
+            return self['__dst_id']
+
+    @staticmethod
+    def link_ptr(src_id=None, dst_id=None):
+        """
+        init from src_id or dst_id attributes - at least one must be provided
+        """
+        return Link.Link_Ptr(src_id, dst_id)