diff --git a/src/tosca/parser.py b/src/tosca/parser.py
index 7c14243..acbd5f1 100644
--- a/src/tosca/parser.py
+++ b/src/tosca/parser.py
@@ -98,20 +98,24 @@
     @staticmethod
     def populate_model(model, data):
         for k,v in data.iteritems():
-            setattr(model, k, v)
+            # NOTE must-exists is a TOSCA implementation choice, remove it before saving the model
+            if k != "must-exist":
+                setattr(model, k, v)
         return model
 
     @staticmethod
     def _translate_exception(msg):
         readable = []
         for line in msg.splitlines():
-            if line.strip().startswith('MissingRequiredFieldError'):
-                readable.append(line)
-            if line.strip().startswith('UnknownFieldError'):
+            if line.strip().startswith('MissingRequiredFieldError') or \
+                    line.strip().startswith('UnknownFieldError') or \
+                    line.strip().startswith('ImportError') or \
+                    line.strip().startswith('InvalidTypeError') or \
+                    line.strip().startswith('TypeMismatchError'):
                 readable.append(line)
 
         if len(readable) > 0:
-            return '/n'.join(readable)
+            return '\n'.join(readable) + '\n'
         else:
             return msg
 
@@ -184,23 +188,33 @@
             self.ordered_models_template = self.get_ordered_models_template(self.ordered_models_name, self.templates_by_model_name)
 
             for recipe in self.ordered_models_template:
-                # get properties from tosca
-                data = recipe.templates[recipe.name]['properties']
-                # [] get model by class name
-                class_name = recipe.type.replace("tosca.nodes.", "")
-                model = GRPCModelsAccessor.get_model_from_classname(class_name, data, self.username, self.password)
-                # [] populate model with data
-                model = self.populate_model(model, data)
-                # [] check if the model has requirements
-                # [] if it has populate them
-                model = self.populate_dependencies(model, recipe.requirements, self.saved_model_by_name)
-                # [] save, update or delete
-                if self.delete and not model.is_new:
-                    model.delete()
-                elif not self.delete:
-                    model.save()
+                try:
+                    # get properties from tosca
+                    if not 'properties' in recipe.templates[recipe.name]:
+                        data = {}
+                    else:
+                        data = recipe.templates[recipe.name]['properties']
+                        if data == None:
+                            data = {}
+                    # [] get model by class name
+                    class_name = recipe.type.replace("tosca.nodes.", "")
+                    model = GRPCModelsAccessor.get_model_from_classname(class_name, data, self.username, self.password)
+                    # [] populate model with data
+                    model = self.populate_model(model, data)
+                    # [] check if the model has requirements
+                    # [] if it has populate them
+                    model = self.populate_dependencies(model, recipe.requirements, self.saved_model_by_name)
+                    # [] save, update or delete
 
-                self.saved_model_by_name[recipe.name] = model
+                    if self.delete and not model.is_new:
+                        model.delete()
+                    elif not self.delete:
+                        model.save()
+
+                    self.saved_model_by_name[recipe.name] = model
+                except Exception, e:
+                    print "[XOS-TOSCA] Failed to save model: %s [%s]" % (class_name, recipe.name)
+                    raise e
 
         except ValidationError as e:
             if e.message:
@@ -216,6 +230,6 @@
                 exception_msg = e._state.details
             raise Exception(exception_msg)
         except Exception, e:
-            raise e
+            raise Exception(e)
 
 
diff --git a/src/tosca/xtarget/tosca.xtarget b/src/tosca/xtarget/tosca.xtarget
index 5faafee..f0eb78b 100644
--- a/src/tosca/xtarget/tosca.xtarget
+++ b/src/tosca/xtarget/tosca.xtarget
@@ -5,6 +5,20 @@
 
 node_types:
 
+    # Example usage:
+    #
+    # <node-name>:
+    #     type: tosca.nodes.{{ m.name }}
+    #     properties:
+    #       must-exist: true # optional to reference models created in other recipes
+{%- for f in (m.fields + xproto_base_fields(m, proto.message_table)) | sort(attribute='name') %}
+{%- if not f.link and xproto_tosca_required(f.options.null, f.options.blank, f.options.default) %}
+    #       {{ f.name }}: <value>
+{%- endif -%}
+{%- endfor %}
+
+
+
     tosca.nodes.{{ m.name }}:
         derived_from: tosca.nodes.Root
         description: {% if m.options.description -%}{{ m.options.description}}{% else%}"An XOS {{ m.name }}"{%- endif %}
@@ -27,6 +41,16 @@
 
     {% for l in m.links %}
     {%- if l.link_type == "manytoone" -%}
+
+
+    # Identify a {{ l.peer.name }} that belongs to a {{ m.name }}
+    #
+    # example usage:
+    # requirements:
+    #   - {{ l.src_port }}:
+    #       node: <node-name>:
+    #       relationship: tosca.relationships.BelongsToOne
+
     tosca.relationships.BelongsToOne:
         derived_from: tosca.relationships.Root
         valid_target_types: [ tosca.capabilities.xos.{{ l.peer.name }} ]