# Re: definition of ConstraintSet and concepts for the algorithm

From: Jim Barnett <1jhbarnett@gmail.com>
Date: Sat, 08 Feb 2014 10:38:47 -0500
Message-ID: <52F64F87.9020102@gmail.com>
To: Martin Thomson <martin.thomson@gmail.com>
CC: media capture <public-media-capture@w3.org>
Yes, the point may well need elaboration, perhaps in the body of the
text rather than in the definitions for the algorithm.  As for the
style, I'm convinced that Addison, Steele, Cardinal Newman, William
Ellery Channing and some of the other great writers could have produced
a perfectly precise spec in fluid, natural prose.  The rest of us are
stuck with legalese.

- Jim
On 2/7/2014 6:42 PM, Martin Thomson wrote:
> That works, though I wonder if you don't need some expository text for
> the second point.  Constraints are designed to aid in managing access
> to resources that are made accessible to multiple actors and any
> existing constraints applied by one actor limit the "effective
> Capability" of that resource in subsequent attempts by other actors to
> access (and constrain) that resource.
>
> This is just an observation, but though this is all correct, it's
> starting to sound a little too much like legalese for me to be
> perfectly comfortable.  That said, it seems like it's perfectly
> natural in the W3C to use such language.
>
> On 7 February 2014 11:26, Jim Barnett <1jhbarnett@gmail.com> wrote:
>> Combining the existing text and ideas from Harald and Martin, I've come up
>> with the following definitions to go with the algorithm in the current text.
>> Let me know what you think.
>>
>> We refer to each immediate attribute of a ConstraintSet (as defined by
>> HasOwnProperty) as a 'constraint' since it is intended to constrain the
>> corresponding Capability of the Constrainable object to a value that is
>> within the range or list of values it specifies.
>> We refer to the "effective Capability" C of an object O as the possibly
>> proper subset of the possible values of C (as returned by getCapabilities)
>> taking into consideration environmental limitations and/or restrictions
>> placed by other constraints.  For example given a ConstraintSet that
>> constrains Capabilities aspectRatio, height and width, the values assigned
>> to any two of the Capabilities limit the effective Capability of the third.
>> The set of effective Capabilities may be platform dependent.  For example,
>> on a resource-limited device it may not be possible to set Capabilities C1
>> and C2 both to 'high', while on another less limited device, this may be
>> possible.
>> A set of values for the Capabilities of an object O satisfy ConstraintSet CS
>> if each value a) is in the range of the corresponding effective Capability
>> of O, and b) is in the range or list of values specified by the
>> corresponding constraint in CS, if there is one, and c) there is no
>> constraint in CS that does not correspond to a Capability of O. (Note that
>> although this definition ignores the difference between mandatory and
>> optional ConstraintSets, the algorithm below distinguishes between them.)
>> A set of ConstraintSets CS1...CSn (n >= 1) can be satisfied by an object O
>> if it is possible to choose a sequence of values for the Capabilities of O
>> that satisfy CS1...CSn simultaneously.
>> To apply a set of ConstraintSet CS1...CSn  to object O is to choose such a
>> sequence of values that satisfy CS1...CSn and assign them as the settings
>> for the properties of O.
>>
>> When applyConstraints is called, the UA must queue a task to run the
>> following steps:.etc. .
>>
>> --
>> Jim Barnett
>> Genesys

--
Jim Barnett
Genesys
Received on Saturday, 8 February 2014 15:39:27 UTC

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