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Re: Grandparent <state> for <final>

From: Jim Barnett <1jhbarnett@gmail.com>
Date: Thu, 29 Jun 2017 09:25:09 -0400
To: Stefan Radomski <radomski@tk.tu-darmstadt.de>
Cc: "www-voice@w3.org (www-voice@w3.org)" <www-voice@w3.org>
Message-ID: <9974876e-eee7-d01c-e76a-8ea006f79338@gmail.com>
Stefan,

   What you are proposing is simply a different definition of being in a 
final state than the one the group used.  Your definition is a 
reasonable alternative, and if there ever is another version of SCXML we 
will consider it.  However this is not an erratum.  Specifically:

1) The current definition is the one the group explicitly chose/voted for.

2) The current definition does not cause any inconsistencies in the spec.

When the group was still working, we kept an issues list for proposals 
to be considered in a future version of the spec. That's where your 
definition would go.  Now that the Voice Browser Group is closed, I 
don't know if there will ever be another version, but it is too late to 
make changes to SCXML 1.0.

- Jim


On 6/29/2017 3:29 AM, Stefan Radomski wrote:
>
>> On Jun 29, 2017, at 01:05, Jim Barnett <1jhbarnett@gmail.com 
>> <mailto:1jhbarnett@gmail.com>> wrote:
>>
>> 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.
>>
> Is that so? I'd say if every active atomic state in the children of a 
> parallel is final, then the parallel is done. Regardless of where 
> those final states are in the hierarchy.
>>
>> 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.
>>
> In my opinion, it breaks encapsulation as you need to be aware of 
> structures higher up the ancestry chain.
>>
>> 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.
>>
> "After an interpreter enters a final state s, it checks whether any 
> ancestor parallel state p of s has only final states left in the 
> intersection between its atomic children and the active states. It 
> raises `done.state.[p@id]` if that is the case." I don't see why a 
> higher level <final> state should block the semantic at all - could 
> you elaborate on that?
>
> Stefan
>>
>> - 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 Thursday, 29 June 2017 13:25:45 UTC

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