RE: [plcs] RE: [plcs-dex] RE: [plcs] Classification of SI Units

plcs message

Automatic conversion is in several cases dangerous and not allowed. Conversions of most thecnical values must be verified/certified by engineering and officially released. One example is tolerances which is not just a matter of conversion but following specific intervals. Lockheed Martin, I'm sure, is well aware of conversion from inches to mm (some of the lunar vehicles do at least).

-----Original Message-----
From: Tim King [mailto:tmk@lsc.co.uk]
Sent: den 9 augusti 2004 19:36
To: 'Barker, Sean (UK)'; Hendrix, Thomas E; ian.bailey@eurostep.com; plcs@lists.oasis-open.org; plcs-dex@lists.oasis-open.org
Subject: RE: [plcs] RE: [plcs-dex] RE: [plcs] Classification of SI Units

A mixed economy of units is not the problem that I was thinking of (apologies that I had not spotted that potential confusion). My concern is in how we would solve that mixed economy. The mixed economy that I see to be the problem is in the solution. We have the options of using either or both the reference data library ontology and the full representation of derivation and conversion of units using the STEP constructs. However, if some people avoid the full richness of the STEP representation and only use the reference data then their exchange files are not compatible with those who use the STEP constructs and do not wish to build class library processing & reasoning into their applications.

-----Original Message-----
From: Barker, Sean (UK) [mailto:sean.barker@baesystems.com]
Sent: 09 August 2004 15:44
To: Tim King; Hendrix, Thomas E; ian.bailey@eurostep.com; plcs@lists.oasis-open.org; plcs-dex@lists.oasis-open.org
Subject: RE: [plcs] RE: [plcs-dex] RE: [plcs] Classification of SI Units

Somewhere in the Stanford Uni. site is a full ontology for units., including SI and Imperial. We have used this in ontology negotiation to automatically convert from one system to another where one or other system implements only a subset of the ontology - e.g. converting Newtons to Kg.m/s/s. It is my belief that this sort of capability will become useful in the next few years (though not the immediate future), and that we should not do things that prevent it happening. The question becomes, not should we try and avoid having a "mixed economy", but, do we understand enough about what these sort of approaches when we try to implement them?

Sean Barker
ATC Filton
0117 302 8184
-----Original Message-----
From: Tim King [mailto:tmk@lsc.co.uk]
Sent: 02 August 2004 17:23
To: 'Hendrix, Thomas E'; Tim King; ian.bailey@eurostep.com; plcs@lists.oasis-open.org; plcs-dex@lists.oasis-open.org
Subject: [plcs] RE: [plcs-dex] RE: [plcs] Classification of SI Units

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Whoops! I too was not totally on the ball and had forgotten that context_dependent_unit is what I have previously used for the examples that I gave; and now that I think again, I am happy with that choice. The conversions I then stored as a property of 5 (value) litres per can (derived unit) for paint and 10 litres per can.

Cheers,
Tim.
-----Original Message-----
From: Hendrix, Thomas E [mailto:thomas.e.hendrix@boeing.com]
Sent: 02 August 2004 17:13
To: Tim King; ian.bailey@eurostep.com; plcs@lists.oasis-open.org; plcs-dex@lists.oasis-open.org
Subject: RE: [plcs-dex] RE: [plcs] Classification of SI Units

Sorry, by "everything" I just meant that for example inches should be expressed as conversion_based_unit from si centi-metre, etc, instead of being context_dependent_unit. PDM schema gives example of "kit" as a context_dependent_unit. Your examples seem like a grey area, where the best approach could depend on the business context.

.
-----Original Message-----
From: Tim King [mailto:tmk@lsc.co.uk]
Sent: Monday, August 02, 2004 12:16 AM
To: Hendrix, Thomas E; Tim King; ian.bailey@eurostep.com; plcs@lists.oasis-open.org; plcs-dex@lists.oasis-open.org
Subject: RE: [plcs-dex] RE: [plcs] Classification of SI Units

Dear Tom,
Thanks for your view. On the whole this is the way that I see things. However, when I raised this is one PLCS session at Fort Lauderdale, there were voices suggesting that the RDL would handle all cases. I suppose that derivation and conversion are possible through the reference data (somehow) but I am leery of breaking compatibility with other STEP APs. We are in the territory as to whether the reference data should only extend the AP or whether replacing valid STEP constructs is permissible.

I am not entirely sure what you mean when you say "to base everything on SI". I am wondering whether this is possible with all the forms of units of measure. What comes to mind are things like "can" and "reel". Perhaps you mean these should be conversion based units and "can" should be converted to "5 litres" for instance (cans of paint) and reel to "10 metres" (reels of wire)? The only problem that comes to mind is that the paint cans might be 5 litres but the oil cans 10 litres.

Cheers,
Tim.
-----Original Message-----
From: Hendrix, Thomas E [mailto:thomas.e.hendrix@boeing.com]
Sent: 30 July 2004 22:17
To: Tim King; ian.bailey@eurostep.com; plcs@lists.oasis-open.org; plcs-dex@lists.oasis-open.org
Subject: RE: [plcs-dex] RE: [plcs] Classification of SI Units

If we classify as-is, Conversion_based_unit and Derived_unit are never used, each unique unit value generates a separate external class in a one-level system, with no semantic relationships among the classes. Does this adds much?

Or maybe can we create some analog of the derivation and conversion structure as (static) class structure? I am not seeing a nice way to do this.

So I prefer to build derived units and conversion based units explicitly where applicable. Further it seems reasonable to me to base everything on SI. That is the 203 recommended practise.

-----Original Message-----
From: Tim King [mailto:tmk@lsc.co.uk]
Sent: Thursday, July 29, 2004 1:20 AM
To: 'ian.bailey@eurostep.com'; plcs@lists.oasis-open.org; plcs-dex@lists.oasis-open.org
Subject: [plcs-dex] RE: [plcs] Classification of SI Units

I think the problem has another related aspect. Use of classification can also cover another key feature within the modules for units, namely derived units. If one has the unit "m/s^2" does one classify as is or does one use the drived unit feature to build the unit from the constituent units? My preference would be to build the derived unit because this supports full dimensional analysis for validation of calculations. However, for those who do not see the benefit of this capability, quite clearly classification offers an attractive "short cut" that circumvents the complexity that is necessary to represent the full derivation. If we end up with a "mixed economy" then we will not be able fully to harmonise and compare data sets.

-----Original Message-----
From: Ian Bailey [mailto:ian.bailey@eurostep.com]
Sent: 28 July 2004 21:55
To: plcs@lists.oasis-open.org; plcs-dex@lists.oasis-open.org
Subject: [plcs] Classification of SI Units

Hi Folks,
I've been working on the "representing_properties_numerically" capability, where an issue has been raised by Tom Hendrix. We have been classifying (i.e reference data) the units which are used with properties. Tom has pointed out that the STEP models have a full breakdown of SI units already and there could be a conflict between the value set there and what is classified. Has anyone looked into this issue ?

Regards
--
Ian Bailey
Eurostep Limited - www.eurostep.com
t&f: +44 (0) 20 7378 1894
m: +44 (0) 7768 892362

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