Operators that take two kinds of input (Stream + table / relation + table) has only one port.
But only stream/relation can trigger the operator execution, and tables are only used for static information. In case 
of
StreamProjectionAndFilter, it is only invoked when a message arrives on the stream at the bottom, but logically it 
looks
 like the two table "invoke" this as well due to the fact they all look like inputs. I suppose they all are inputs but 
the table data
is pulled whereas (and only when) the stream is pushed. Is there a way we can make this more obvious with the 
operator? 

Suggestion 1.
An indication on the connector between the operators. For example, a dash line for the output of tables to
show that they are not providing events, but a referenced data source. 

Suggestion 2.
Show table port differently as following

Suggestion 3.
Make tables being connected to the top of the StreamProjectionAndFilter rather than the left-hand-side