public Connection(IGraphNode start, IGraphNode end)
{
if (start.Equals(Activity.End))
{
throw new Exception("Forbidden: END node cannot be connection's start node.");
}
if (end.Equals(Activity.Start))
{
throw new Exception("Forbidden: START node cannot be connection's end node.");
}
Validate(start, end);
startNode = start;
start.RegisterConnection(this);
endNode = end;
end.RegisterConnection(this);
}