W3C home > Mailing lists > Public > www-voice@w3.org > April to June 2017

Re: Grandparent <state> for <final>

From: Jim Barnett <1jhbarnett@gmail.com>
Date: Wed, 28 Jun 2017 19:05:15 -0400
To: www-voice@w3.org
Message-ID: <0d5abd57-6f3a-dc82-1b46-02fe542dfce0@gmail.com>
Interesting case.  I'm pretty sure that:

1) The current language was what the group wanted (i.e., it's not an error)

2) We never discussed this case.

However, to expand a bit further:  suppose we add a <final> child to 
state p0_s0 (i.e. a sibling state to p0_s0_s0).  In that case we 
wouldn't want entering p0_s0_s0_f0 to put the parent p0_s0 in a final 
state - only entering its direct <final> child should do that.  The 
current language forces authors to be explicit about final states, and 
is easy to understand, but in examples like yours it can lead to 
somewhat counter-intuitive results.   If we try to get 'final-hood' to 
be inherited upward, but for the inheritance to be blocked by the 
presence explicit higher-level <final> states, the definition gets very 
complicated.

- Jim


On 6/28/2017 6:10 PM, Gavin Kistner wrote:
> A couple years ago I wrote a Lua interpreter for SCXML[1]. Stefan R. 
> just filed a bug with it[2]. At the core of the issue is whether the 
> following SCXML parallel should be 'in a final/done state' after being 
> entered:
>
> <parallel id="p0">
> <state id="p0_s0">
> <state id="p0_s0_s0"><final id="p0_s0_s0_f0"/></state>
> </state>
> <state id="p0_s1">
> <state id="p0_s1_s0"><final id="p0_s1_s0_f0"/></state>
> </state>
> </parallel>
>
> My interpreter fires "done.state.p0_s0_s0" and "done.state.p0_s1_s0". 
> However, it does not cause "p0_s0" or "p0_s1" to be considered in a 
> final state, and therefore does not consider the parallel to be in a 
> final state.
>
> On the one hand, this clearly looks like a bug in my interpreter 
> against how I would *expect* the specifications to handle this 
> situation. On the other hand, the specifications+errata only appear to 
> cover situations where a <parallel> is exactly a *grandparent* of the 
> <final>, not any further ancestor.
>
> Section 3.7 of the spec says:
>
> "When the state machine enters the <final> child of a <state> element 
> […] generate the event done.state.id [...] where id is the id of the 
> parent state. Immediately thereafter, if the parent <state> is a child 
> of a <parallel> element, and all […] other children are also in final 
> states […] generate the event done.state.id where id is the id of the 
> <parallel> element."
>
> This only covers exactly the parent of the <final>, not any 
> grandparent <state> or great-grandparent <parallel>.
>
> Further, the pseudo-code for Appendix D explicitly only handles one 
> level at the end of enterStates(), and also only handles one level for 
> the definition of isInFinalState().
>
>
> If Stefan (and my) belief about how this should behave is correct, 
> then (a) the prose in 3.7 needs to be modified via errata, and (b) the 
> isInFinalState() pseudo-code should be modified to recurse, and (c) we 
> need to discuss whether grandparent <state> also fire "done.state.xxx" 
> events when their child state becomes in a final state, and if so, 
> modify the pseudo-code in enterStates() to do so.
>
> If we're wrong—if grandparent states do not get this event fired, are 
> not considered in a final state, and if the parallel in the example 
> above should also not be in a final state—I'd be very interested to 
> hear some arguments for this.
>
> [1] https://github.com/Phrogz/LXSC
> [2] https://github.com/Phrogz/LXSC/issues/1
>
> --
> (-, /\ \/ / /\/
Received on Wednesday, 28 June 2017 23:05:51 UTC

This archive was generated by hypermail 2.3.1 : Wednesday, 28 June 2017 23:05:57 UTC