C2MS12 — Using REQ Messages for 'Publish'

The "Publish" MEP second paragraph talks about using either MSG or REQ messages as a means of publishing. I think this could use some revisiting.

It seems on that a REQ message "may or may not require a response. For example, one component may request another component to take some action and does not need to know immediately if the action was successful or not." f(section 6.3.2.1, pg 15). This is then enabled by specifying a BOOLEAN value for "RESPONSE" indicating whether a reponse is expected in a REQ message.

To me, it seems like not expecting a response when issuing a REQ message is a corner case. Even in the example above, how do I know that ANY component received the REQ? I would prefer to say that components that process a REQ message are expected to respond AT LEAST with a RESP Message acknowledging receipt. If the sender chooses not to look for one, fine, but it seems like an odd pattern to make a request and ignore whether anyone heard you.

This would aid in simplifying the Publish MEP to reduce it to just MSG. Actually, if we don't do this, we need to fix the sequence diagram on pg 24, anyway, because as shown it's incorrect; requiring sending a MSG before sending a REQ. It's really meant to be either-or. So, if we remove REQ as a Publish mechanism, the diagram will be adjusted to be correct. If we don't remove it, we need to split the SD into two separate diagrams.

With all this in mind, I'd suggest:

• that the Publish MEP use only MSG Messages, which is what they are intended for
• and stating that REQ messages expect a response, even if it is only an acknowledgement (this would also remove the RESPOSE:BOOLEAN field from REQ messages.
• this results in modifying the Sequence Diagram for Publish MEP (Note that this diagram is actually incorrect, anyway, because as shown, it says that to Publish, the publisher sends a MSG and then a REQ.) At a minimum, this diagram needs to be fixed, even if we don't make the semantic changes described here.

Note that if we remove "RESPONSE:BOOLEAN" concept, this affects the following:
8.4.1.3 Directive Request Contents
8.10.1.3 Command Request Message Contents
8.12.1.3 Simple Service Request Message Contents

Additionally, we'd need to look for scattered text in the spec that says REQ does not require a response.