[QUANTITY] Pulling it all together - missing some things

[Brian Thomas]

On Friday 23 May 2003 06:47 am, David Berry wrote:
> Reading the proposal for Quantity given by Steve Lowe and Jonathan
> McDowell I realise it is quite close in many respects to the way we have
> been handling similar problems within the UK Starlink project. For
> comparison I have attached a 3 page description outlining the Starlink
> approach on the [QUANTITY] wiki page:
>
> http://www.ivoa.net/twiki/bin/view/IVOA/QuantityModel

 	David, all,

	After reading this, I saw that it is missing some important  meta-data. To illustrate,
	I fall back on XDF, where "quantity" looks like "parameter" which holds one or more
        "values". Parameter has the means to specify things like inequalities and special
	computer-oriented meta-data like NaN, which you can see in this snippet of the
	XDF dtd for example:

<!ELEMENT value (#PCDATA)>
<!ATTLIST value
        valueId ID #IMPLIED
        valueRef IDREF #IMPLIED 
        special (infinite | infiniteNegative | noData | notANumber | underflow | overflow | disabled) #IMPLIED
        inequality (lessThan | lessThanOrEqual | greaterThan | greaterThanOrEqual) #IMPLIED
        positiveErrorValue NMTOKEN #IMPLIED
        negativeErrorValue NMTOKEN #IMPLIED
>

	You already have errors taken care of, but are missing the "special" and "inequality"
	stuff. Special numbers are those which the computer may represent by a certain string,
	say "-9.99" but wont be recognizable as "notANumber" without the meta-data to point it out.
	Ditto for doing any "censored" data that involves upper/lower - limits. This is handled by 
	the "inequality" meta-data. Some examples:

	<parameter name="quantity" description="a value less than 5">
                <value inequality="lessThan">5</value>
        <parameter>

	<parameter name="quantity 2" description="a quantity with infinite value">
                <value special="infinite"/>
        </parameter>

	You can also treat lists of mixed numbers and special values in this manner, e.g.

        <parameter name="quanity 3 list" description="a list of things, one of which is NaN">
               <dataFormat notANumber="-9.99"><float width="5" precision="2"/></dataFormat>
               <valueList>0.00 1.00 2.00 3.00 -9.99 5.00</valueList>
        </parameter>


	
										=b.t.


>
> David
>
> P.S. I'm off on holiday now for a week (sampling the Scottish rain) so
> I'll be out of touch for a while.



  * Dr. Brian Thomas 

  * Code 630.1 
  * Goddard Space Flight Center NASA

  *   fax: (301) 286-1775
  * phone: (301) 286-6128

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