Dear Stan, (01)
Thank you for your e-mail. I flagged the treatment of "Rockwell Hardness" up
as an "unsolved problem", because I feel that more discussion is required. A
possible view is as follows: (02)
An approach to Rockwell hardness
--------------------------------
It seems straightforward that Rockwell_C_hardness_(150kg) is a
kind_of_quantity. Within this kind_of_quantity, the there is a
magnitude_of_quantity that is expressed by the quantity_value (55,
Rockwell_C_hardness_(150_kg)). So far so good - the UML model in the Wiki is
happy with this. Note in this case the reference from the quantity_value is
not a unit but a measurement procedure. (03)
The difficulty is the relationship between my_lump_of_hard_steel and the
magnitude_of_quantity that is expressed as (55,
Rockwell_C_hardness_(150_kg)). I think that it is classification. The
magnitude_of_quantity is the class of objects that have the specified
response the the measurement procedure. Hence in this case, the link between
magnitude_of_quantity and particular_phenomenon_body_or_substance, which is
labelled particular_quantity, is classification. (04)
Another kind of quantity
------------------------
Consider waterline length of a ship. If the ship Medway_Queen has a
waterline length of 20 metres, then we have:
- the particular_phenomenon_body_or_substance that is the Medway_Queen;
- the magnitude_of_quantity thas is expressed by the quantity_value (20, metre);
- the particular_quantity relationship has_waterline_length between the two. (05)
In this case, the particular_quantity relationship is not simply
classification, but is of a special type - has_waterline_length. (06)
Explaining the difference
-------------------------
The relationship has_waterline_length is a shorthand for something quite
complicated. There is a relationship has_extreme_waterline_point_pair
between a ship and a point pair. Just as the magnitude_of_quantity that is
expressed as (55, Rockwell_C_hardness_(150_kg)) can be regarded as a class
with solid objects as members, the magnitude_of_quantity that is expressed
as (20, metre) can be regarded as a class that has point pairs as members. (07)
Hence for the ship there are two relationships:
has_extreme_waterline_point_pair and classification, which are composed to
give has_waterline_length. This seems to be a very common case, where the
nature of the relationship between a physical object and a
magnitude_of_quantity embodies a great deal of domain knowledge, and the
kind_of_quantity is simple. (08)
For Rockwell hardness the relationship is simply classification, and the
domain knowledge is embodied in the kind_of_quantity. (09)
If does not worry me that these cases are different. I think that the model
in the Wiki handles both. (010)
Best regards,
David (011)
p.s. I have taken the liberty of cc'ing this discussion to the forum because
it may be of general interest. (012)
At 11:23 30/07/2009 -0700, you wrote:
>David,
>
>Thank you for sharing this. With respect to the "unsolved problem" related
>to the Rockwell Hardness example in the UnitsML wiki, the VIM model is that
>a quantity is a property to which a number can be assigned with respect to a
>reference. In VIM (1.1), the reference can be a measurement unit, a
>measurement procedure, or a reference material. VIM (1.26) considers
>Rockwell Hardness to be an ordinal quantity, which is a quantity defined by
>a measurement procedure. Your wiki model and the SysML approach only
>consider measurement units. This might account for the difficulty cited in
>the wiki. IMO, a normative model of quantities should include the other
>references besides measurement units, to handle the general case.
>
>Best regards,
>
>Stan
>
>> -----Original Message-----
>> From: David Leal [mailto:david.leal@xxxxxxxxxxxxxxxxxxx]
>> Sent: Thursday, July 30, 2009 7:45 AM
>> To: Ed Barkmeyer; Mark H Linehan; Stan Hendryx; Donald Chapin
>> Subject: Strawman from current discussion and UnitsML
>>
>> Dear All,
>>
>> I have added some notes about how the strawman UML model derived from the
>> recent discussion relates to UnitsML and other work to
>> http://ontolog.cim3.net/cgi-bin/wiki.pl?UoM_Ontology_Standard .
>>
>> As you would expect the alignment with UnitsML is close.
>>
>> Best regards,
>> David (013)
============================================================
David Leal
CAESAR Systems Limited
registered office: 29 Somertrees Avenue, Lee, London SE12 0BS
registered in England no. 2422371
tel: +44 (0)20 8857 1095
mob: +44 (0)77 0702 6926
e-mail: david.leal@xxxxxxxxxxxxxxxxxxx
web site: http://www.caesarsystems.co.uk
============================================================ (014)
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