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RE: Device Description definition

From: Rotan Hanrahan <rotan.hanrahan@mobileaware.com>
Date: Thu, 1 Mar 2007 14:31:15 -0000
Message-ID: <D5306DC72D165F488F56A9E43F2045D3DD753F@FTO.mobileaware.com>
To: "Jo Rabin" <jrabin@mtld.mobi>, <public-ddwg@w3.org>

By immutable I mean that the value can be assigned once, and when that
value is known it will remain unchanged. Typically, the physical width
of the screen is an immutable property. We could then refer to the set
(or class) of devices that have a particular screen width. In other
words, the definition of the set includes the fact that the devices have
a ScreenWidth property, and that the property has a particular value.

We could further add a longer set of similarly immutable properties
until we eventually identify something we would recognise as a
particular model of a device from a particular manufacturer. This is the
level of identification that I believe will be most common, but I do not
preclude other possible set membership definitions.

The tie-in between the "device type properties" and the "device instance
properties" in the example I gave relates to the data types used to
describe the permitted and current screen orientations. If I use a
number to represent orientation, then it is wise that we agree on what
the numbers mean. Consider a slightly more complex example of an
immutable property: "The set of permitted orientations and the default
orientation". It is clear that within this complex type we should ensure
that "default orientation" is a subset of "permitted orientations". Now,
how do we ask the question: "is the screen currently in the default
orientation?". For such a question to be formulated programmatically, it
is necessary to ensure that the data types are comparable. This is best
achieved by using essentially the same data types. (It avoids the need
for translation.)

This is why it is sensible to work closely with other groups (like the
DCI group within the DIWG, and the groups from the OMA). By keeping our
data types, vocabularies, ontologies (etc.) in harmony, we can help
avoid future compatibility issues.

The way you are formulating the ontology/type-def/instance seems to
capture this idea.

> If the class allows only one value, the property is immutable.

The value may in fact belong to a collection type. So a particular set
of permitted orientations would be an example of the only value allowed
for a property. That property we may call "PermittedOrientations". There
is a second atomic property which has a value from the set value
assigned to PermittedOrientations, and this one we will call
CurrentOrientation. This latter value may vary. Each device in the set
of devices will have such a property, but the value of the property does
not form part of the definition of the set. (The fact of *having* such a
property *may* form part of the definition of the set.)

"Class" would work fine for me.

---Rotan.

-----Original Message-----
From: Jo Rabin [mailto:jrabin@mtld.mobi] 
Sent: 01 March 2007 14:07
To: Rotan Hanrahan; public-ddwg@w3.org
Subject: RE: Device Description definition

My comments in line:

> -----Original Message-----
> From: Rotan Hanrahan [mailto:rotan.hanrahan@mobileaware.com]
> Sent: 01 March 2007 13:02
> To: Jo Rabin; public-ddwg@w3.org
> Subject: RE: Device Description definition
> 
> The DI glossary describes a device as an "apparatus". The dictionary
> would seem to allow both physical and non-physical examples. Therefore
I
> think Jo is correct that the mention of "hardware and software" is
> redundant. But this might just be an example of "DI Lore and Wisdom",
> and perhaps to the casual reader this subtlety may go unobserved.
> 

Sorry, I should have been clearer in my citation (from
http://www.w3.org/TR/di-gloss/)

Device
    An apparatus through which a user can perceive and interact with the
Web.

User Agent
    A client within a device that performs rendering.
    Browsers are examples of user agents, as are web robots that
automatically traverse the web collecting information.

Client
    The role adopted by an application when it is retrieving and/or
rendering resources or resource manifestations.

So I infer that a user agent is a client (which is an application) which
forms part of a device which is an apparatus. 

[As a side note, I see that robots are user agents, which are clients in
a device. Which would lead you to infer that a robot is part of an
apparatus through which a user can perceive and interact with the Web.
Which I think is only arguably true.]

> In which case, there is an argument for revising the DI definition of
> Device to add such a clarification.

I think I agree.

> 
> Not all of the properties of a specific device are the territory of
some
> other group. A specific device may belong to a class of device (a set
of
> devices) defined according to having the same value for some immutable
> property. 

Right, I think this is where my confusion sets in. I can see what you
are saying, I think, but surely the important thing is that the
attributes that are immutable, as you call them, are only immutable
because the device is of a type where there is only one value that an
instance of the device can have for that attribute.

If the device type definition says 'screen width: 120' then all
instances have an immutable property of screen width 120.


Those immutable properties are clearly the kind of data of
> interest to this group. Properties that may vary, on the other hand,
are
> the territory of other groups.
> 
> A device may have the ability to display in two orientations:
landscape
> and portrait. This ability is an immutable property of the device.
> 
> At a particular point in time, a specific device may be rendering in
one
> of the two orientations. The orientation in use may vary over time.
This
> property is not something that can be managed by a repository.
> 
> In the example, we are dealing with two related properties:
>   Permitted Orientations
>   And
>   Current Orientation

I don't think I quite see it that way. It doesn't seem to quite tie
together the device type properties with the device instance properties.


It seems to me that it [could] work like this:

- the ontology says that there is an attribute called screen orientation
that has a value space of landscape and portrait.
- the device type definition says this device type has screen
orientation landscape or portrait
- the instance says it has landscape (for example)

i.e. the device type definition contains permissible values for the
attributes and the device instance has actual values for _the same_
attributes.

So back to the example above, 
- the ontology says screen width is an integer (ignoring facets, just
for a moment)
- the device type definition says screen width is 120
- the device instance definition therefore necessarily says screen width
is 120

> 
> If you indicate a set of immutable properties, and values for those
> properties, then you can define a set of devices as all those devices
> that have those particular values. This was the "set" concept I had in
> mind in the definitions I have suggested recently.

But, the fact that the screen orientation can be either landscape or
portrait is a shared property of all devices in a class, even though
their instances may have different property values to each other. I
think my confusion crucially rests on the point that I think instance
attributes are the same as type (or class) attributes. So to me
immutable properties are neither here nor there. If the class allows
only one value the property is immutable.

> 
> To answer another of your questions: I think it is the attributes and
> their range of values that characterise a device. In this, I also
would
> permit the value "Not Applicable" (distinct from "Not Known", which is
> another issue entirely).

Yes, agree strongly - but this is a feature of the ontology, surely,
which would allow either of those as a value for any attribute?

> 
> I'm a bit worried about the use of the word "type". I'll have to think
> more about it.

Would class work better for you?

Jo

> 
> -----Original Message-----
> From: public-ddwg-request@w3.org [mailto:public-ddwg-request@w3.org]
On
> Behalf Of Jo Rabin
> Sent: 01 March 2007 12:35
> To: public-ddwg@w3.org
> Subject: RE: Device Description definition
> 
> 
> I am running along behind on this ... trying to keep up, forgive me:
> 
> Commenting on: "Device Description - A set of attributes which
> characterizes that part of the delivery context directly related to
the
> hardware and software of a device. These attributes adhere to the
> Delivery Context Ontology."
> 
> I thought a device, as defined by DI, is hardware and software?
> Specifically it includes the user agent. So what point are we making
by
> saying 'related to the hardware and software of a device' that is
> different to saying 'relating to a device'?
> 
> A further confusion, on my part, is that when we say 'a device' we
don't
> mean 'a specific device', because as discussed (accidentally on the
> other list, I think) the exact values for the properties of a specific
> device at a point in time is the territory of some other group. So do
we
> in fact mean 'devices' or better still 'classes of devices' or perhaps
> better even than that 'type of device'?
> 
> My next confusion is - is it the attributes that characterise the type
> of device, or is it the attributes and their possible values that
> characterise the type of device?
> 
> And as a possibly rather pedantic kicker, when we say 'set', do we
mean
> that the same set is chosen for all device classes or do we mean, more
> loosely, that it is a collection of attributes - some of which may be
> present for some descriptions but not others?
> 
> So if I am heading down a track that is comprehensible to anybody, do
we
> mean:
> 
> Device Description - a collection of attributes chosen from the
Delivery
> Context ontology, together with the values for those attributes that
> characterise a type of device.
> 
> Thanks
> Jo
> 
> 
> > -----Original Message-----
> > From: public-ddwg-request@w3.org [mailto:public-ddwg-request@w3.org]
> On
> > Behalf Of Rhys Lewis
> > Sent: 01 March 2007 12:08
> > To: Rotan Hanrahan; Smith, Kevin, VF-Group; public-ddwg@w3.org
> > Subject: RE: Device Description definition
> >
> >
> > Hello everyone,
> >
> > I think we are making progress!
> >
> > One comment is that 'they' are not attribute/value pairs. T think we
> > should simply refer to 'them' as attributes, which is the term from
> the
> > delivery context definition.
> >
> > Also, I think we should use the term ontology rather than
vocabulary.
> We
> > probably should also define a term like Delivery Context Ontology
> (I'll
> > volunteer to suggest a definition) and then refer to that from the
> > definition for device description.
> >
> > That would lead to something like:
> >
> > Device Description - A set of attributes which characterizes that
part
> of
> > the delivery context directly related to the hardware and software
of
> a
> > device. These attributes adhere to the Delivery Context Ontology.
> >
> > I tweaked the wording to match that from the delivery context
> definition.
> >
> >
> > Best wishes
> > Rhys
> >
> > -----Original Message-----
> > From: public-ddwg-request@w3.org [mailto:public-ddwg-request@w3.org]
> On
> > Behalf Of Rotan Hanrahan
> > Sent: 01 March 2007 11:19
> > To: Smith, Kevin, VF-Group; public-ddwg@w3.org
> > Subject: RE: Device Description definition
> >
> >
> > I like this definition. Good body, delicate nose, hint of oak...
> >
> > We should view this proposal in the context of the DI Glossary [1].
> The
> > important terms there are Device and Delivery Context. It seems to
me
> that
> > the "mash-up" fits well with these existing definitions.
> >
> > ---Rotan.
> >
> > [1] http://www.w3.org/TR/di-gloss/
> >
> >
> >
> > -----Original Message-----
> > From: public-ddwg-request@w3.org [mailto:public-ddwg-request@w3.org]
> On
> > Behalf Of Smith, Kevin, VF-Group
> > Sent: 01 March 2007 11:14
> > To: public-ddwg@w3.org
> > Subject: RE: Device Description definition
> >
> >
> > How about a mash-up? Definition 2.0, as it were:
> >
> > Device description - a collection of attribute-value pairs, adhering
> to a
> > known vocabulary, that apply to each member of a set of devices and
> > describe the specific part of the delivery context directly related
to
> the
> > hardware and software of the device.
> >
> > Kevin
> >
> >
> >
> >
> > -----Original Message-----
> > From: Rotan Hanrahan [mailto:rotan.hanrahan@mobileaware.com]
> > Sent: 01 March 2007 11:09
> > To: Smith, Kevin, VF-Group; public-ddwg@w3.org
> > Subject: RE: Device Description definition
> >
> > The most recent one that I posted to the public list was actually:
> >
> > Device description - a collection of attribute-value pairs, adhering
> to a
> > known vocabulary, that apply to each member of a set of devices.
> >
> > This incorporates the point made my Rhys regarding ontology
> (vocabulary)
> > though does not specifically mention Delivery Context, which I think
> might
> > be a good idea. Suggestions anyone?
> >
> > ---Rotan.
> >
> >
> >
> > -----Original Message-----
> > From: public-ddwg-request@w3.org [mailto:public-ddwg-request@w3.org]
> On
> > Behalf Of Smith, Kevin, VF-Group
> > Sent: 01 March 2007 11:05
> > To: public-ddwg@w3.org
> > Subject: RE: Device Description definition
> >
> >
> > Hi everyone,
> >
> > So (I think) the latest proposal for the definition was from Rhys,
> > namely:
> >
> > Device description: describing that specific part of the delivery
> context
> > directly related to the hardware and software of the device.
> >
> > ...where delivery context is defined as "A set of attributes that
> > characterizes the capabilities of the access mechanism, the
> preferences of
> > the user and other aspects of the context into which a web page is
to
> be
> > delivered." This (to me) covers Jo's point about current and
possible
> > values.
> >
> > Alternatively we have Rotan's defintion:
> >
> > Device description - a collection of attribute-value pairs that
apply
> to
> > each member of a set of devices.
> >
> > Are there any further comments on either? I personally think both
are
> > correct, but that it makes sense to associate the definition with
the
> > delivery context as per Rhys' wording.
> >
> > Cheers,
> > Kevin
> >
> >
> >
> >
> >
> 
Received on Thursday, 1 March 2007 14:31:41 UTC

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