fix comments from the PR

Author: stanimir-atscale

sml-reference/composite-model.md

@@ -38,7 +38,7 @@ metrics:
 classDiagram
     CompositeModel ..> ModelReference
     CompositeModel ..> MetricReference
-    Model *-- Aggregate
+    CompositeModel *-- Aggregate
     Aggregate *-- AttributeReference
 namespace CompositeModels{
     class CompositeModel{
@@ -120,7 +120,8 @@ The `metrics` property supports the following properties:
 - **Required:** N
 
 The `aggregates` property in a composite model file enables you to add
-user-defined aggregates (UDAs).
+user-defined aggregates (UDAs).They include metrics or attributes from different
+models within the composite model.
 
 In general, we recommend relying on the aggregate tables
 automatically generated by the semantic engine. However, there are cases