Notification, WSDL 2.0 MEPs, cardinality

[David Hull <dmh@tibco.com>]

I'm not sure how much attention to give this, but since we're in Last Call, we might want to see if there's anything we can say right now, leaving the full details for later discussion.

Following the example of WSDL 1.1, WSDL 2.0 defines a family of four one-way operations, namely [robust] {in,out}-only.  These are explicitly defined as consisting of "exactly one message".  This stands in contrast to notification semantics, which may produce zero or more messages.

I can see several ways to resolve this, though there may be others:

1. Consider notification as producing zero or more operations, each consisting of exactly one message.
2. Define four more operations, say zero-or-more [robust] {in,out}-only.
3. Define some means, say an attribute, of specifying the cardinality of an operation.  Notification can then be modeled by out-only, with zero-or-more cardinality.
4. Define some means of specifying a grammar for MEPs, so one could distinguish, say
• in, fault | out*  That is, in followed by a fault or by some sequence of out
  
• in, (fault | out)* That is, in followed by some sequence of fault and out mixed together.

(1) is certainly the least disruptive to the present ecosystem, but it seems to miss the idea that separate notifications are part of a series that can be paused, resumed, queued, played back, stopped, etc.

(2) is just ugly

(3) seems attractive, but if we want to go that far, why not go all the way to (4).

(4), on the other hand, is powerful but clearly heavyweight.