[Obi-devel] need suggestion on the parent class of pH

[Jie Zheng]

Hi All,

pH: A dimensionless concentration notation which denotes the acidity of
a solution in terms of activity of hydrogen ions (H+).

It is a subclass of dimensionless unit and concentration unit in UO. I
imported it into OBI as a subclass of concentration unit. Is it fine?
Any comment on it?

Thanks,

Jie

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[Philippe Rocca-Serra]

Hi Jie,

It could be better to place it as a subclass of concentration.

we say this solution has a pH of 4 but we don't say this solution is 4
pH (as we may do in "this solution of HCl is 1M")

I find the definition of dimensionless unit weird, almost antinomic: A
derived unit which is a standard measure of physical quantity consisting
of only a numerical number without any units.

dimensionless measurement would be ok as a class for that definitions.

HTH

Philippe

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[Jie Zheng]

Hi Philippe,

Thanks for your comments.

Jie

[Fostel, Jennifer (NIH/NIEHS) [E]]

folks do talk about pH units.
pH is the negative log of [H+], thus derived from a concentration

-----Original Message-----
From: Philippe Rocca-Serra [mailto:ro...@ebi.ac.uk]
Sent: Monday, March 29, 2010 5:03 PM
To: Jie Zheng
Cc: OBI Developers
Subject: Re: [Obi-devel] need suggestion on the parent class of pH

Hi Jie,

It could be better to place it as a subclass of concentration.

we say this solution has a pH of 4 but we don't say this solution is 4 pH (as we may do in "this solution of HCl is 1M")

I find the definition of dimensionless unit weird, almost antinomic: A derived unit which is a standard measure of physical quantity consisting of only a numerical number without any units.

dimensionless measurement would be ok as a class for that definitions.

HTH

Philippe

Jie Zheng wrote:
> Hi All,
>
> pH: A dimensionless concentration notation which denotes the acidity
> of a solution in terms of activity of hydrogen ions (H+).
>
> It is a subclass of dimensionless unit and concentration unit in UO. I
> imported it into OBI as a subclass of concentration unit. Is it fine?
> Any comment on it?
>
> Thanks,
>
> Jie
>
> ----------------------------------------------------------------------

> -------- Download Intel® Parallel Studio Eval Try the new

[Jie Zheng]

That is what I thought.

Thanks, Jennifer.

[Jessica Turner]

From the workshop last week we were using clinical scores as an example of a dimensionless unit--e.g., you can get a 20 on the Scale for the Assessment of Negative Symptoms, but you don't have 20 units of anything. It's just the score on that instrument (::duck::). I hadn't looked at the definition of dimensionless unit very closely though--the requirement that it's a "standard measure of a physical quantity" may be too stringent for clinical scores.

 

Jess

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email: jtu...@mrn.org

[Phillip Lord]

It isn't a unit though. Unit, I think, implies linearity; so, 2 is twice
as much as 1.

pH is not the negative log of [H+], but a scale defined against a set of
standard solutions (as there is no transform from [H+] to activity of
H+). It's similar to things like the Beaufort, Richter or Scoville
scales.

It all depends on how much you want to make the distinction. I would say
that this form of scale is like a unit, but distinct from it. It needs a
new concept.

Phil

--
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Lecturer in Bioinformatics, Email: philli...@newcastle.ac.uk
School of Computing Science, http://homepages.cs.ncl.ac.uk/phillip.lord
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[Ryan Brinkman]

Phil,

Do you have a proposal? That would be very helpful.

Cheers,
Ryan

On 2010-03-30, at 2:39 AM, "Phillip Lord"
<philli...@newcastle.ac.uk> wrote:

> I would say
> that this form of scale is like a unit, but distinct from it. It
> needs a
> new concept.
>
> Phil

------------------------------------------------------------------------------

[Fostel, Jennifer (NIH/NIEHS) [E]]

Wikipedia...

The pH probe measures pH as the activity of hydrogen ions surrounding a thin-walled glass bulb at its tip. The probe produces a small voltage (about 0.06 volt per pH unit) that is measured and displayed as pH units by the meter. For more information about pH probes, see glass electrode.

 

i think we are making too fine a distinction to introduce a different concept.  Furthermore, BS would not approve of introducing any concepts into OBI.

 

...jennifer

[Phillip Lord]

Well, we all seem to agree that it's dimensionless, although I can't
find "dimensionless unit" in the current version of the ontology.

I don't think that it's a unit because of it's lack of any form of
additivity. Nor is it a category, because it is ordered.

So, following with IAO current practice of describing the label, rather
than the actual thing of interest, I think we need a new type of label
-- that is measurement scale label. This has the property that
categorical labels lack -- they are ordered. pH falls into this
category, as do my other two examples -- wind and spicyness. There are
many more categories like this.

I think that this has the advantage of being most correct, although it's
more complex. So, I would also be happy enough with introducing new
concepts directly underneath measurement unit label and ignoring the
distinction.

Phil

Ryan Brinkman <rbri...@bccrc.ca> writes:
> Phil,
>
> Do you have a proposal? That would be very helpful.
>
> Cheers,
> Ryan
>
>
> On 2010-03-30, at 2:39 AM, "Phillip Lord"
> <philli...@newcastle.ac.uk> wrote:
>
>> I would say
>> that this form of scale is like a unit, but distinct from it. It
>> needs a
>> new concept.
>>
>> Phil
>
>

--

Phillip Lord, Phone: +44 (0) 191 222 7827
Lecturer in Bioinformatics, Email: philli...@newcastle.ac.uk
School of Computing Science, http://homepages.cs.ncl.ac.uk/phillip.lord
Room 914 Claremont Tower, skype: russet_apples
Newcastle University, msn: m...@russet.org.uk
NE1 7RU

------------------------------------------------------------------------------

[Phillip Lord]

"Fostel, Jennifer (NIH/NIEHS) [E]" <fos...@niehs.nih.gov> writes:
> Wikipedia... The pH probe measures pH as the activity of hydrogen ions
> surrounding a thin-walled glass bulb at its tip. The probe produces a
> small voltage (about 0.06 volt per pH unit) that is measured and
> displayed as pH units by the meter. For more information about pH
> probes, see glass electrode.

Also from wikipedia

"pH is not precisely p[H], but takes into account an activity factor."

and

"hydrogen ion activity coefficients cannot be measured directly by any
thermodynamically sound method"

and

"the pH scale is defined in practice as traceable to a set of standard
solutions whose pH is established by international agreement"

> i think we are making too fine a distinction to introduce a different
> concept.

Yes, we may be. It depends whether chemists read OBI. Defining pH as a
concentration will really get their goat.

> Furthermore, BS would not approve of introducing any concepts into
> OBI.

Barry likes to make an obscure distinction between "entities as they
exist in reality" and "concepts". I think it's too fine a distinction to
introduce a different word. So I use "concept" because it's shorter.
This is true regardless of Barry's approval.

Phil

------------------------------------------------------------------------------

[Melanie Courtot]

Based on a chemical definition of pH (http://antoine.frostburg.edu/chem/senese/101/acidbase/faq/what-is-pH.shtml
), there seems to be 2 different definitions:
1. The Theoretical Definition pH is a logarithmic measure of hydrogen
ion concentration [..] The pH scale was defined because the enormous
range of hydrogen ion concentrations found in aqueous solutions make
using H+ molarity awkward. For example, in a typical acid-base
titration, [H+] may vary from about 0.01 M to 0.0000000000001 M. It is
easier to write "the pH varies from 2 to 13".

2. The Experimental Definition IUPAC has endorsed a pH scale based on
comparison with a standard buffer of known pH using electrochemical
measurements. The IUPAC pH scale is very slightly different from the
theoretical definition, since it considers factors that are not
included in the (thermodynamic) theoretical pH.

I am more familiar with definition 1., and would have considered pH as
a concentration unit.

On 30-Mar-10, at 9:41 AM, Phillip Lord wrote:

>
> Well, we all seem to agree that it's dimensionless, although I can't
> find "dimensionless unit" in the current version of the ontology.
>
> I don't think that it's a unit because of it's lack of any form of
> additivity.

Could you expand on that? I consider units as ways of measuring
qualities of things using a standardized scale - whether it be linear
or logarithmic.

> Nor is it a category, because it is ordered.
>
> So, following with IAO current practice of describing the label,
> rather
> than the actual thing of interest, I think we need a new type of label
> -- that is measurement scale label. This has the property that
> categorical labels lack -- they are ordered. pH falls into this
> category, as do my other two examples -- wind and spicyness.

http://www.seismo.unr.edu/ftp/pub/louie/class/100/magnitude.html -
they seem to consider Richter magnitude as units "...This accounts for
the usual spread of around 0.2 magnitude units that you see reported
from different seismological lab..." or "...The uncertainty in an
estimate of the magnitude is about plus or minus 0.3 units..."

Similary for the Scoville: http://en.wikipedia.org/wiki/Scoville_scale
" The number of Scoville heat units (SHU) indicates the amount of
capsaicin present."

> There are
> many more categories like this.

We did have similar discussion during the workshop regarding
handedness scale, and have been discussing on the IAO side about how
to represent scales. We added "categorical measurement datum" to start
with.

See related discussion at http://code.google.com/p/information-artifact-ontology/issues/detail?id=78
, http://code.google.com/p/information-artifact-ontology/issues/detail?id=79
and the proposal to have a call to add those at http://groups.google.com/group/information-ontology/browse_thread/thread/b90e9898b8a99240

Melanie

---
Mélanie Courtot
TFL- BCCRC
675 West 10th Avenue
Vancouver, BC
V5Z 1L3, Canada

[Alan Ruttenberg]

On Tue, Mar 30, 2010 at 12:48 PM, Phillip Lord
<philli...@newcastle.ac.uk> wrote:
> "Fostel, Jennifer (NIH/NIEHS) [E]" <fos...@niehs.nih.gov> writes:
>> Wikipedia... The pH probe measures pH as the activity of hydrogen ions
>> surrounding a thin-walled glass bulb at its tip. The probe produces a
>> small voltage (about 0.06 volt per pH unit) that is measured and
>> displayed as pH units by the meter. For more information about pH
>> probes, see glass electrode.
>
> Also from wikipedia
>
> "pH is not precisely p[H], but takes into account an activity factor."

This is apparently a comment that is relevant to use of all
concentrations. From http://en.wikipedia.org/wiki/Activity_(chemistry)
:

In chemical thermodynamics activity (symbol: a) is a measure of the
“effective concentration” of a species in a mixture. By convention, it
is treated as a dimensionless quantity, although its actual value
depends on customary choices of standard state for the species. The
activity of pure substances in condensed phases (solid or liquids) is
normally taken as unity. Activity depends on temperature, pressure and
composition of the mixture, among other things. For gases, the
effective partial pressure is usually referred to as fugacity.
The difference between activity and other measures of composition
arises because molecules in non-ideal gases or solutions interact with
each other, either to attract or to repel each other. The activity of
an ion is particularly influenced by its surroundings.
Activities should be used to define equilibrium constants but, in
practice, concentrations are often used instead. The same is often
true of equations for reaction rates. However, there are circumstances
where the activity and the concentration are significantly different
and, as such, it is not valid to approximate with concentrations where
activities are required.

> and
>
> "hydrogen ion activity coefficients cannot be measured directly by any
> thermodynamically sound method"

Single hydrogen ion activity.

> and
>
> "the pH scale is defined in practice as traceable to a set of standard
> solutions whose pH is established by international agreement"

This language does not speak to the nature of the quantity. In general
there will be many cases where a unit will be associated with an assay
that is the socially agreed upon way of measuring quantities. That
doesn't mean the unit means the assay.

The passage from the IUPAC document on Ph says
(http://www.iupac.org/reports/provisional/abstract01/rondinini_prs.pdf)

3.1 Relation to SI System.

Since pH is not measured in terms of a fundamental (or base) unit of
any measurement system, it has become common practice to regard pH
measurements as being traceable to their definition. A more
satisfactory alternative is now available, since it has been accepted
that measurements of chemical properties can be incorporated within
the internationally-accepted SI system of measurement if they can be
traced to measurements made using a method that fulfils the definition
of a “primary method of measurement” (1).

http://www.bipm.org/utils/en/pdf/blevin1998-EN.pdf

For measurements of quantity of matter, i.e. for metrology in
chemistry, measurements
consistent with the definition of the SI unit (the mole) cannot in
practice be achieved through the comparison of physical artefacts because the
number of substances that would have to be compared individually is very
l a rge. Instead, the Consultative Committee for Amount of Substance
(CCQM), set up by the CIPM in 1993, is identifying a range of primary
methods of measurement. A primary method of measurement is a method
having the highest metrological qualities, whose operation can be completely
described and understood, for which a complete uncertainty statement can be
written down in terms of SI units, and whose results are therefore accepted
without reference to a standard of the quantity being measured

Note that there is no question here that what is being measured is an
amount of matter.

I also note that the language "ph Unit" is in common usage, and so
should be mentioned somewhere in OBI, It would be called a unit of a
quantity of dimension 1 in SI nomenclature. Other such "units" are
radians and steradians.

http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf

"(b) The radian and steradian are special names for the number one
that may be used to convey
information about the quantity concerned. In practice the symbols rad
and sr are used where
appropriate, but the symbol for the derived unit one is generally
omitted in specifying the
values of dimensionless quantities."

Ok, well there's some more background. I don't think we're done yet,
but I need to go to a call.

-Alan

[Phillip Lord]

Melanie Courtot <mcou...@gmail.com> writes:
>> I don't think that it's a unit because of it's lack of any form of
>> additivity.
>
> Could you expand on that? I consider units as ways of measuring qualities of
> things using a standardized scale - whether it be linear or logarithmic.

If we have a unit, say, Q, if you know how to measure 1Q, then you
should be able to work out how to measure 2Q.

So, if I give you a 1m rule, then m is a unit because you can also
measure 2m. I'm not suggesting that the relationship always needs to be
linear. For example, given a 1m rule, you can also measure a area or a
volume. But you can't measure a 2m^2 volume, only a 4m^2 area, or an
8m^3 volume.

This is true for a concentration, but because of the activity component
for pH is, strictly, not true for pH.

>> Nor is it a category, because it is ordered.
>>
>> So, following with IAO current practice of describing the label, rather
>> than the actual thing of interest, I think we need a new type of label
>> -- that is measurement scale label. This has the property that
>> categorical labels lack -- they are ordered. pH falls into this
>> category, as do my other two examples -- wind and spicyness.
>
> http://www.seismo.unr.edu/ftp/pub/louie/class/100/magnitude.html -
> they seem to consider Richter magnitude as units "...This accounts for the
> usual spread of around 0.2 magnitude units that you see reported from
> different seismological lab..." or "...The uncertainty in an estimate of the
> magnitude is about plus or minus 0.3 units..."

The Richter scale is based on a measurement from a particular piece of
apparatus, and saturates. I know relatively little about the Richter
scale, though, so I might be wrong here.

The Beaufort scale I know more about, and is based around whether flags
stand up, or whether you get white horses. Compare this form of
empirical scale to "wind speed of 10ms^-1" -- the latter clearly is a
unit. We can say that "20ms^1 is twice as fast as 10ms^1; however all we
can say about Beaufort 8 is that it's windier than Beaufort 5.

>
> Similary for the Scoville: http://en.wikipedia.org/wiki/Scoville_scale " The
> number of Scoville heat units (SHU) indicates the amount of capsaicin
> present."
>

If you read down, you will see that Scoville is actually a scale based
on the ability of tasters to perceive heat under standardized
conditions. Again, it's an empirical scale. It happens to be
more or less proportional to capsaicin content.

Scoville has the advantage that it can also be meaningfully applied to
substances other than capsaicin, including those which are hotter, while
it is not really meaningful, for example, to describe capsaicin
concentrations greater than pure.

>> There are many more categories like this.
>
> We did have similar discussion during the workshop regarding handedness scale,
> and have been discussing on the IAO side about how to represent scales. We
> added "categorical measurement datum" to start with.
>
> See related discussion at
> http://code.google.com/p/information-artifact-ontology/issues/detail?id=78
> , http://code.google.com/p/information-artifact-ontology/issues/detail?id=79
> and the proposal to have a call to add those at http://groups.google.com/group/information-ontology/browse_thread/thread/b90e9898b8a99240
>

I agree; it's nearly the same issue. Categories, such as handedness are
totally unordered, though. Scales are ordered but with an uncertain
relationship between the items; just greater than or less than.

Given the existence of categorical measurement data, it seems that there
is already a good design pattern in OBI for dealing with this form of
data. So the two options, as I see them are, either make the distinction
using this pattern (which is more correct, but more complex) or ignore
the distinction (which is less correct, but simpler). Gains and losses
either way.

My suspicion is that our target audience would want to have their cake
and eat it. They would say that pH is a unit and we are being picky
about the distinction, but would be unhappy about clinical scales (for
example) being considered units.

Phil

[Phillip Lord]

Alan Ruttenberg <alanrut...@gmail.com> writes:
>> "pH is not precisely p[H], but takes into account an activity factor."
>
> This is apparently a comment that is relevant to use of all
> concentrations. From http://en.wikipedia.org/wiki/Activity_(chemistry)

This covers much the same ground, but is longer.

>> and
>>
>> "hydrogen ion activity coefficients cannot be measured directly by any
>> thermodynamically sound method"
>
> Single hydrogen ion activity.

You can't meaningfully define the concentration of an single ion, I
fear.

>> and
>>
>> "the pH scale is defined in practice as traceable to a set of standard
>> solutions whose pH is established by international agreement"
>
> This language does not speak to the nature of the quantity.

This language does not speak to my understandability. What does this
mean?

> In general there will be many cases where a unit will be associated
> with an assay that is the socially agreed upon way of measuring
> quantities. That doesn't mean the unit means the assay.

It doesn't mean that it doesn't either. And in this case, it does. There
are a set (not one) of standard assays which define a scale.

> I also note that the language "ph Unit" is in common usage, and so
> should be mentioned somewhere in OBI,

Synonyms.

> It would be called a unit of a quantity of dimension 1 in SI
> nomenclature. Other such "units" are radians and steradians.

No. Radians are additive, with a clearly defined relationship between
what "1 radian" and "2 radians" mean.

Phil

[Larisa Soldatova]

Hi,

we have to send the BMC copyright agreement form (the article is
original, etc. - a standard one). I can do that if you authorize me.
Please send your objections if you do not as soon as possible.

Below are the comments for a camera ready version:

- Please change the references to BioMed Central style - cited in the
main text by numbers in square brackets, with a numbered list at the
end of the manuscript. The references should be numbered in the order
in which they are cited in the main text
- Table 1 is larger than 1 page and so might be better as an
additional file (see our attached notes on additional files)

I will change the reference style, but I think to ignore the second
comment. It would be inconvenient for the readers to look at a
separate file every time they wish to check information about the
terms used in the paper.

Objections?

Thanks,
Larisa

[Yongqun He]

I agree that we should keep Table 1 in the main text instead of as an additional file.

Since current Table 1 is large, is it possible to separate it into two tables? For example, we can separate the table to one table containing terms with OBI Ids and another table containing terms from other ontologies.

Oliver

>>> Larisa Soldatova <l...@aber.ac.uk> 4/1/2010 7:08 AM >>>

**********************************************************
Electronic Mail is not secure, may not be read every day, and should not be used for urgent or sensitive issues

[Larisa Soldatova]

yes, it is a good suggestion.

Another option is to make two tables: one with classes, another with relations. It is almost how it is now. Terms table nicely fits to 1 page.

Larisa

[Alan Ruttenberg]

Approve

[James Malone]

+1 (if needed)

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Hinxton,
Cambridge, CB10 1SD,
United Kingdom
Tel: + 44 (0) 1223 494 676
Fax: + 44 (0) 1223 492 468

[Larisa Soldatova]

I put the latest version of the paper to SVN. It has 2 tables: classes and relations. I thought that it would be more natural devision as in this case we do not need a column 'parent class' and I could change the name of the column 'sources and term IDs' to 'sources' in the table 2.

I can revert it back if you wish to.

I plan to send the copyright agreement and a camera ready version on the Monday. 

We now can officially reference the paper as in press.

Larisa

[Yongqun He]

That's great. Thanks,

Oliver

>>> Larisa Soldatova <l...@aber.ac.uk> 4/1/2010 10:03 AM >>>

[Fostel, Jennifer (NIH/NIEHS) [E]]

activity ~ concentration
you can measure H+ dissociation, i.e. free H+ concentration in water, i.e. acidity, i.e. pH
i just checked with our head of chemistry who says "of course pH is a concentration unit".

-----Original Message-----
From: Phillip Lord [mailto:philli...@newcastle.ac.uk]
Sent: Wednesday, March 31, 2010 10:00 AM
To: Alan Ruttenberg
Cc: OBI Developers
Subject: Re: [Obi-devel] need suggestion on the parent class of pH

[Melanie Courtot]

On 31-Mar-10, at 6:49 AM, Phillip Lord wrote:

>
> Melanie Courtot <mcou...@gmail.com> writes:
>>> I don't think that it's a unit because of it's lack of any form of
>>> additivity.
>>
>> Could you expand on that? I consider units as ways of measuring
>> qualities of
>> things using a standardized scale - whether it be linear or
>> logarithmic.
>
> If we have a unit, say, Q, if you know how to measure 1Q, then you
> should be able to work out how to measure 2Q.
>
> So, if I give you a 1m rule, then m is a unit because you can also
> measure 2m. I'm not suggesting that the relationship always needs to
> be
> linear. For example, given a 1m rule, you can also measure a area or a
> volume. But you can't measure a 2m^2 volume, only a 4m^2 area, or an
> 8m^3 volume.
>
> This is true for a concentration, but because of the activity
> component
> for pH is, strictly, not true for pH.

The SI defines meter as a base unit, while m2 or m3 are SI derived
units: http://physics.nist.gov/cuu/Units/units.html

I understand what you mean, I guess my question is where is it coming
from :)

Units as I see them are an agreed upon convention (and for that reason
I start liking the unit label proposal, which reflects that it is a
social type of artifact). Groups of people agree on using a meter rule
to refer to the same length, or rely on people taste's to assess
spiciness.

I am not sure that it does matter if the scale is empirical or
determined by an measuring device: for example if we were to invent a
machine measuring spiciness, I suspect we would align the output
measurement with the existing Scoville scale.

I would agree with that.

I added a link to this thread to the agenda of the April 13th call: http://code.google.com/p/information-artifact-ontology/wiki/Meeting_notes_20100413
. Alan will be hosting the call, just add your name to the list of
attendees on the wiki or ping him if you want to join the discussion.

On a side note, the BIPM had a workshop last year about physiological
units and their relation to SI units: http://www.bipm.org/en/events/physiological_quantities/
. I couldn't find a summary of the outcome of this meeting, only link
is restricted access. They also seem to have quite a few articles
regarding pH, for example http://iopscience.iop.org/
0026-1394/46/3/007/ (linked from http://tinyurl.com/yku6fcj)

Cheers,
Melanie

[Melanie Courtot]

+1

Thanks for taking care of this.
Melanie

---

Mélanie Courtot
TFL- BCCRC
675 West 10th Avenue
Vancouver, BC
V5Z 1L3, Canada

------------------------------------------------------------------------------

[Phillip Lord]

Sure, but a concentration unit of what? Clearly not H+ (i.e. a free
proton). It's an effective activity, which makes it different from, say,
the concentration of SO4+ in a sulphuric acid solution. If this were not
the case, why have a pH at all? We could just use log of the molarity.
We could calculate this directly, from the amount of stuff we have added
to the water.

As you say, we may be splitting hairs here that don't need to be split;
I'm inclined to think that this is the case here; the abstraction of pH
to being a unit of concentration is probably close enough. As I said
earlier, I think it's probably what the majority of users will expect,
which provides a good enough justification for the simpler solution to
me.

Phil

"Fostel, Jennifer (NIH/NIEHS) [E]" <fos...@niehs.nih.gov> writes:

> activity ~ concentration
> you can measure H+ dissociation, i.e. free H+ concentration in water,
> i.e. acidity, i.e. pH i just checked with our head of chemistry who
> says "of course pH is a concentration unit".
>

------------------------------------------------------------------------------

[Phillip Lord]

Melanie Courtot <mcou...@gmail.com> writes:
>> So, if I give you a 1m rule, then m is a unit because you can also
>> measure 2m. I'm not suggesting that the relationship always needs to be
>> linear. For example, given a 1m rule, you can also measure a area or a
>> volume. But you can't measure a 2m^2 volume, only a 4m^2 area, or an
>> 8m^3 volume.
>>
>> This is true for a concentration, but because of the activity component
>> for pH is, strictly, not true for pH.
>
>
> The SI defines meter as a base unit, while m2 or m3 are SI derived units:
> http://physics.nist.gov/cuu/Units/units.html
>
> I understand what you mean, I guess my question is where is it coming from :)

As I've said elsewhere, I think that in the case of pH, we are probably
making distinctions that do not need to be made. I think, though, in
general, there is a difference between a scale and a unit. My
distinction would be that, give "1" you can work out what "2" means.

Of course, this does get muddy. The Beaufort scale is a example, because
the original, empirically defined measure has been mapped to wind speed.
So, in a sense, now Beaufort is a scale fitted over a unit.

>> If you read down, you will see that Scoville is actually a scale based
>> on the ability of tasters to perceive heat under standardized
>> conditions. Again, it's an empirical scale. It happens to be
>> more or less proportional to capsaicin content.
>>
>> Scoville has the advantage that it can also be meaningfully applied to
>> substances other than capsaicin, including those which are hotter, while
>> it is not really meaningful, for example, to describe capsaicin
>> concentrations greater than pure.
>>
>
> Units as I see them are an agreed upon convention (and for that reason I start
> liking the unit label proposal, which reflects that it is a social type of
> artifact). Groups of people agree on using a meter rule to refer to the same
> length, or rely on people taste's to assess spiciness.

I think that this is fairly dodgy ground. Most of the things that we are
modelling are "conventional"; height, colour, legs/feet/toes. This
doesn't really help with the modelling though. Nor does it relate to the
distinction that I am trying to make; if you know what 1m is then you
can define any length.

The unit label proposal is wrong for a different reason; it's modelling
the unimportant thing not the important thing. It's rather like saying
"this is a tin with a label for baked beans on it", rather than "this is
a tin of baked beans". However, IAO has decided that this inconvenient
model is the way forward; at this stage, it probably makes more sense to
be consistently broken, rather than right half the time.

> I am not sure that it does matter if the scale is empirical or
> determined by an measuring device: for example if we were to invent a
> machine measuring spiciness, I suspect we would align the output
> measurement with the existing Scoville scale.

We can and we have! Same thing as Beaufort.

>> My suspicion is that our target audience would want to have their cake
>> and eat it. They would say that pH is a unit and we are being picky
>> about the distinction, but would be unhappy about clinical scales (for
>> example) being considered units.
>
> I would agree with that.
>
> I added a link to this thread to the agenda of the April 13th call:
> http://code.google.com/p/information-artifact-ontology/wiki/Meeting_notes_20100413
> . Alan will be hosting the call, just add your name to the list of attendees
> on the wiki or ping him if you want to join the discussion.

I don't think I will be there I am afraid. As far as I can see, the
issue has been discussed; I think that there is a distinction that could
be made here, but I don't see a driving use case for making it. Given
that, the simpler solution (pun!) is probably the best.