RE: [xml-dev] ANN: a portable data component -- length

["Costello, Roger L." <costello@mitre.org>]

Liam wrote:

>> Here is the altitude of an aircraft, expressed in both feet and meters:
>> 
>>      <altitude>
>>          <feet>12000</feet>
>>          <meters>3657.6</meters>
>>      </altitude>
>> 
>> It is important that the two length values are consistent:
>
> The right way to mark this up in most cases is to store only one value
> and convert as needed.
>
> See Normal Form in database theory: information should never be
> duplicated. That way it can't get out of sync.

With the portable length component, the concern about values getting out of sync no longer applies. The component is designed to ensure that all values are consistent (i.e., in synch). Its internal assertions check that all values are consistent.

The portable length data component is for those times when you want to provide users a length in a range of units and with a guarantee that all values are consistent.

/Roger