[QUANTITY] Why quantities always have errors (Was: Re: [QUANTIT] Use-cases, role in larger scheme)

[DIDELON Pierre]

> From brian.thomas at gsfc.nasa.gov Mon Nov 17 18:31:06 2003
> From: Brian Thomas <brian.thomas at gsfc.nasa.gov>
> To: DIDELON Pierre <dide at discovery.saclay.cea.fr>
> Subject: Re: [QUANTITY] Why quantities always have errors (Was: Re: [QUANTIT] Use-cases, role in larger scheme)
> Date: Mon, 17 Nov 2003 12:30:22 -0500
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> On Monday 17 November 2003 12:14 pm, DIDELON Pierre wrote:
> > If you have to pass a parameter to an application, to specify some input
> > value, you may need to transmit a value (without error), it can even be a
> > flag. This is a very immediat example, and we can not rule out in VO (IMO),
> > the usage of numbers without error, once for all,
> > even if today it seems more natural to you,
> > SOME PEOPLE outside here want to use numbers without errors,
> > and ask for that possibility several times on the list (and off the list),
> > and it would certainly be appropriate in some cases.
> 
> 	This can be resolved by simply choosing a sensible default meaning
> 	for the error == NULL.
> 
> 	I suggest that if an error isnt present (e.g. returns null), then its meaning 
> 	is "error, unknown". If you want to create a 'constant' then you would get
> 	something else, e.g. quantity->getError() returns "ExactNoError" class.
> 
> 	And its a pretty trivial detail of construction of the class, I think in terms
> 	of implementation. Say you want to create 2 classes that embody "hardwired"
> 	errors (so implementer doesnt need to thinik about the errors), such as 
> 	"constant" and "parameter",  then, assuming a quantity interface, we have:
> 
> 	class Constant implements Quantity {
> 
> 	ErrorType getError () {
> 		return new ErrorExact();
> 	}
> 
> 	}
> 
> 	and for your "parameter":
> 
> 	class Parameter implements Quantity {
> 
> 	ErrorType getError() {
> 		return new UnknownError();
> 	}
> 
> 	}
> 
> 	Regards,
> 
> 		=b.t.
> 
> 
> -- 
> 
>   * Dr. Brian Thomas 
> 
>   * Code 630.1 
>   * Goddard Space Flight Center NASA
> 
>   *   fax: (301) 286-1775
>   * phone: (301) 286-6128
> 
> 
> 
WHY?
why trying to complicate the smallest and simplest things?
Why not admitting the co-existing of 2 classes, one using the other?
Why not let the one who want to play without error to do so?
Pierre
PS: last mail of today... I'm going home.