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Re: [xml-dev] What is this principle called:"I' send data in my UOM and you convert it, as needed, to your UOM"?


If "UOM" in the subject line means "unit of measure", then one possible name for this principle is "Babel", since it requires (for data exchange) every member in the community to understand the units used by every other member (and if a new member with a new unit joins the community, every other member has to be altered).  But that's not exactly the principle you describe in the text.  In the text, everyone's agreed on decimal values in centimeters as the exchange standard.  The difficulty you cite comes in not having worked out the standard so as to cover all possible values (so there is uncertainty about what the original system should send for the value of 1/3 meter, and how receiving systems should interpret whatever the sending system decides to send).  If it's really true that "exchanging the wrong amount of precision could be catastrophic" you need to work that out.  It's not properly handled by some general principle.  Recall, though, that arbitrary-precision arithmetic is needed in a relatively few applications.  Recall also that if some member of the community literally *requires* data with a certain precision, then the data exchange contract needs to take that into consideration.  In that case, you may not necessarily be able to literally apply the principle "a sender should transmit its original data; it is up to recipients to convert the data, if necessary, to the precision they require" because there may be no sender capable of providing that degree of precision (note that I'm not talking about how many digits are sent, but about the actual precision of the data;  if some recipient system requires 33.33333 and the sender sends 33.30000, that doesn't cut it).

On Sep 9, 2011, at 10:15 AM, Costello, Roger L. wrote:

> Hi Folks,
> Suppose that every member in a community is required to exchange data using one unit of measure. For example, suppose length is required to be expressed as a decimal value in centimeters. Consider a system that internally deals with length measurements in meters. Suppose the system wishes to exchange the value "1/3 meter." Recall that the system is required to exchange values in decimal centimeters. However, there is no exact conversion of "1/3 meter" to centimeters. Should the system send the value 33 cm, 33.3 cm, 33.33333 cm? In the general case, the sending system has no insight into the precision required by recipients. Exchanging the wrong amount of precision could be catastrophic. There is a principle that a sender should transmit its original data (e.g., 1/3 meter); it is up to recipients to convert the data, if necessary, to the precision they require.
> What's the name of the principle? I remember someone on this list talking about it long ago. Perhaps Len? Perhaps Walter Perry? (BTW, anyone know the whereabouts of Walter?)
> /Roger

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