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Re: [SCXML] Question regarding the meaning and purpose of type 'location expression in namelist and param location attributes

From: Ate Douma <ate@douma.nu>
Date: Tue, 28 Oct 2014 15:02:28 +0100
Message-ID: <544FA1F4.6020503@douma.nu>
To: www-voice@w3.org
On 28-10-14 10:39, David Junger wrote:
> Le 28 okt 2014 à 03:31, Ate Douma <ate@douma.nu> a écrit :
>>
>> AFAICT the purpose of the location attribute is only to yield the value at
>> the specified location, not the location itself. But then: why not just and
>> only use the expr attribute always, which should be giving the exact same
>> result, if it targets a datamodel location?
>
> Yes, the location expression itself matters when you use 'location' rather
> than 'value'. It is tied to the use of empty <finalize/> when receiving
> events back from the invocation: in that case, params sent back with the name
> assigned to of one of the locations on starting the invocation will have
> their value copied into that location. I don't recall that there is any other
> use, and that one is pretty marginal. But the definition clearly states that
> a location expression can be any valid left-hand-side value in the ECMAScript
> datamodel. The tests do not currently check for full conformance with this.
> They should use a different name and location, for starters. And they should
> check that params with a name that wasn't associated with a location in the
> <invoke> are not copied.
>
> … or we could just drop this pretty complex, obscure, and marginal feature.

Thanks David, that indeed is an obscure but valid use-case, at least for now :)

This use-case and the (only?) reason for using the location attribute clearly 
can use so more explicit wording in the specification IMO: in the context of the 
<param> element, as well as the main body of the description of the <invoke> 
element.
Right now the only place this seems to be described is in the <finalize> element.

I suggest at least changing the description for the <param> location attribute 
as something like:

   "A location expression [...] that specifies the location in the datamodel to 
retrieve the value from, and write back a value in case of processing returned 
data from an invoked child session with an empty <finalize/> in its <invoke> 
element".

And something similar should be added to the description of the <invoke> 
namelist attribute.

What also needs some further clarification is how a returned value from the 
invoked session should be 'applied' back to the original location, in case of 
the xpath datamodel. The operation seems to be similar like <assign>, but (for 
xpath) should it use type 'replace' or 'replacechildren'?
For <assign> the default is 'replacechildren', but either might make sense for 
<finalize/> handling. The specification says nothing about that though.

Kind regards, Ate

>
> David
>
Received on Tuesday, 28 October 2014 14:02:56 UTC

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