Remarks enhancements for NetworkTopology prior to its Release.

Domains/1-Common/NetworkTopology/NetworkTopology.remarks.md

@@ -15,16 +15,72 @@ The following class-diagram depicts the core mix-ins that address hierarchy of n
 
 ![Network hierarchies](./media/Network-hierarchy-classes.png)
 
+The following class-diagrams depict the two ways that Topology elements can be associated to a network.
+
+![Network break-down](./media/NetworkBreaksDown-classes.png)
+
 The following class-diagram shows the core mix-ins that target connectivity among topology elements.
 
 ![Connectivity](./media/Connectivity-classes.png)
 
+The following class-diagram shows the relationship class to define a topological representation among elements.
+
+![Topological Representation](./media/TopologicalRepresentation-classes.png)
+
 The following class-diagram summarizes the default base classes implementing the provided mix-ins in this schema.
 
 ![Base classes](./media/Default-base-classes.png)
 
 ## Entity Classes
 
+### INetwork
+
+An `INetwork` instance is associated to its `ITopologyElement`s either by the latter being contained in its submodel - the most typical situation - or via `NetworkConsistsOfTopologyElements` relationships between them, but not both. 
+
 ### ITopologyElement
 
-An net:ITopologyElement implementation can signal to be the entry-point of a sub-network at a finer granularity by also mixing-in bis:ISubModeledElement.
+An `ITopologyElement` instance is associated to only one `INetwork` instance either by being contained in its submodel - the most typical situation - or via a `NetworkConsistsOfTopologyElements` relationship between them, but not both. In the former case, the class mixing-in the `INetwork` interface is also expected to mix-in the `bis:ISubModeledElement` interface. Therefore, in that case, the _ModeledElement_ of the `ITopologyElement`'s _Model_ is also its associated `INetwork` instance.
+
+### IEdge
+
+A concrete implementation of this schema shall mix-in the `IEdge` interface when it needs to capture and track links in a graph as _Elements_. That is, Objects with identity and business properties. Another reason leading to the choosing of the `IEdge` interface involves the need of capturing intermediate nodes connected along a link. 
+
+On the other hand, the `NodeConnectsToNode` relationship could be used for simple links with no need to track identity, other business data or intermediate nodes.
+
+An `IEdge` instance connects to its two end-nodes in a graph via the `EdgeStartsAtNode` and `EdgeEndsAtNode` relationships respectively. Intermediate nodes can be connected along an `IEdge` instance by using concepts, rules and patterns defined in the _LinearReferencing_ BIS schema. In that case, the `IEdge` is treated as a _Linear-Element_ along which nodes are linearly-located. To achieve that, the class mixing-in the `IEdge` interface needs to also mix-in the `lr:ILinearElement` interface.
+
+### INode
+
+Connectivity among `INode` instances can be defined via any one of the following three relationships:
+
+- `NodeConnectsToNode`
+- `EdgeConnectsToNode` (abstract), with two concrete relationship classes: `EdgeStartsAtNode` and `EdgeEndsAtNode`.
+- `EdgeInnerConnectsToNode`
+
+### IEdgeInnerConnection
+
+Instances of a class mixing-in the `IEdgeInnerConnection` interface shall be linearly-located along instances of classes mixing-in both `IEdge` and `lr:ILinearElement` interfaces by using the `EdgeInnerConnectsAlongLinearElementEdge` relationship. 
+
+An instance of a class mixing-in `IEdgeInnerConnection` is associated to the `INode` that it linearly-locates via the `EdgeInnerConnectsToNode` relationship.
+
+## Relationship Classes
+
+### NetworkAggregatesSubNetworks
+
+Note that aggregated `INetwork` instances can be contained in the same or different model(s) as their aggregating `INetwork` instance.
+
+### NetworkConsistsOfTopologyElements
+
+The `NetworkConsistsOfTopologyElements` relationship shall only be used when the organization of `ITopologyElement` instances into models is not driven by their associated `INetwork` instances. Since `ITopologyElement`s may be very numerous, creating one of this relationship for each one of those instances increases storage requirements.
+
+### EdgeConnectsToNode
+
+The `EdgeConnectsToNode` relationship can be used to query for any `IEdge` instance connected to an `INode`, disregarding if it is considered as its start or end node.
+
+### NodeConnectsToNode
+
+The `NodeConnectsToNode` relationship could be used to model simple links in a graph, with no need to track identity, other business data or intermediate nodes along them.
+
+### TopologyElementRepresentsElement
+
+`ITopologyElement` instances can be found via the `TopologyElementRepresentsElement` relationship in workflows and trace-operations where the former are not directly manipulated.